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EXAM Master Infectious Disease

Terms in this set (184)

Correct answer:
Acquisition of the enzyme β-lactamase

Explanation
Bacteria carrying a plasmid with the gene for β-lactamase would confer resistance to antibiotics containing the β-lactam ring, such as penicillin and amoxicillin. β-Lactamase is an enzyme that cleaves and inactivates antibiotics like penicillin. The antibiotic penicillin consists of a thiazolidine ring fused to a β-lactam ring (see image). A variable "R" group is attached to the β-lactam ring by a peptide bond. Penicillin inhibits bacterial cell growth by inhibiting the enzyme catalyzing the last step in cell wall synthesis. This step involves the cross-linking of the peptidoglycan strands. Under normal conditions, a peptide bond forms between the terminal glycine on one proteoglycan strand, with the terminal D-Ala-D-Ala unit on the other strand forming the Gly-D-Ala cross-link. The enzyme catalyzing this reaction is glycopeptide transpeptidase. Penicillin inhibits this reaction by mimicking the D-Ala-D-Ala unit, forming a covalent bond between the R-group of penicillin and the active site serine of glycopeptide transpeptidase. The penicilloyl-enzyme complex is enzymatically inactive; therefore, penicillin acts as a transition state analog. Bacterial plasmids often carry genes that confer resistance to a specific antibiotic. Other examples of enzymes carried on plasmids that convey antibiotic resistances are chloramphenicol acetyltransferase, which inactivates chloramphenicol, and phosphotransferases, which modify aminoglycosides such as neomycin and gentamicin. These plasmids can be passed from a resistant to a sensitive bacterial cell, conveying resistance to a particular antibiotic; therefore, many strains of resistant bacteria have arisen, which cause problems in treating the patient.

Resistance to penicillin is not due to mutations in the enzyme glycopeptide transferase, alterations in bacterial cell wall composition, inactivation of the enzyme β-lactamase, or the acquisition of the enzyme phosphotransferase.



References
Deck DH, Winston LG. Beta-Lactam & Other Cell Wall- & Membrane-Active Antibiotics. In: Katzung BG, Trevor AJ. eds. Basic & Clinical Pharmacology, 13e. New York, NY: McGraw-Hill; 2015.
Correct answer:
"You should both take chloroquine weekly starting 1 week before travel."

Explanation
When there is no drug resistance to Plasmodium falciparum (one of the Plasmodium protozoans that causes malaria), weekly chloroquine is the prophylactic drug of choice. It is well-tolerated and can be dosed once weekly rather than daily (hydroxychloroquine is similar for malaria prophylaxis). Travelers should be advised of the risk of malaria, chemoprophylaxis, and personal protection measures. The chloroquine should be dosed weekly starting 1-2 weeks prior to travel, continuing throughout travel, and discontinued 4 weeks after return from a malaria-endemic region. Atovaquone/proguanil, mefloquine, doxycycline, and primaquine can be considered for regions known to have resistant strains of P. falciparum.

P. falciparum can be transmitted via mosquito bites. The risk of malaria infection rises with the number of mosquito bites, but the bite alone does not guarantee malaria, even in endemic regions. The couple should be educated on mosquito bite prevention for their travel. Malaria can be effectively treated in most countries, and patients should also be educated on when and how to seek care when traveling abroad.

Malaria typically causes an influenza-like illness, with fevers, chills, malaise, headaches, and myalgias. Severe cases can progress to seizures and death. Prophylaxis, prompt evaluation, and treatment of malaria are essential for travelers.

Malaria chemoprophylaxis should continue for 7 days to 4 weeks after return from travel. Continuation of treatment for 4 weeks post-return is recommended when using chloroquine, mefloquine, and doxycycline for malarial prophylaxis, and 7 days when using atovaquone/proguanil.

While self-treatment is not ideal, the CDC recommends the use of atovaquone/proguanil (Malarone) if travelers develop symptoms without having utilized malaria prophylaxis. Self-treatment should be temporary, and travelers should be advised to seek medical care. Amoxicillin is not a treatment for malaria.
Correct answer:
Mycobacterium avium complex

Explanation
The patient being described in the above scenario is more than likely suffering from a pulmonary infection secondary to Mycobacterium avium complex (MAC). This type of infection is almost indistinguishable from tuberculosis, but causes a chronic, slowly progressive pulmonary infection in both immunocompromised and immunocompetent patients. Symptoms, when they present, are less severe and more chronic than a Mycobacterium tuberculosis infection. Symptoms most commonly seen include the following (as well as how often they are found): cough (91%), sputum production (85%), weight loss (53%), breathlessness (51%), chest pain (34%), hemoptysis (32%), and fever or night sweats (17%).

Mycobacterium lepraeis the organism that leads to Hansen disease, otherwise known as leprosy. This disease state is rarely seen in the United States but is endemic in tropical and subtropical Asia, Africa, and Central/South America. Signs and symptoms are pale macular/nodular and erythematous skin lesions, as well as superficial nerve thickening, associated anesthesia, and motor abnormalities. Bilateral ulnar neuropathy is highly suggestive of this diagnosis. This is inconsistent with our patient.

Mycobacterium haemophilum, Mycobacterium bovis, and Mycobacterium chelonae are all potential causes of lymphadenitis, also known as scrofula. These organisms are much more prevalent in Northern Europe and signs are not consistent with the patient scenario above.
Correct answer:
Mycoplasma pneumoniae

Explanation
Mycoplasma pneumoniae is a pathogen most frequently associated with atypical community-acquired pneumonia. Atypical pneumonia caused by M. pneumoniae is more common in school children and young adults. The bacterium usually causes asymptomatic infection or mild respiratory disease. Bronchopneumonia involving 1 or more lobes develops in 3-10% of infected persons. Severe infections requiring hospitalization may be seen in the elderly, children with functional asplenia, immune system impairment due to sickle cell disease, and other immunodeficient states like hypogammaglobulinemia. Extra pulmonary manifestations are common. Dermatological, central nervous system, gastrointestinal, and cardiac complications may occur. Hemolytic anemia is recognized as a rare but severe complication of mycoplasma pneumonia, and it is attributed to high titers of cross-reacting cold agglutinins.

A non-specific serological test using human O group RBCs can be used for detecting cold agglutinin titers in pneumonia caused by Mycoplasma pneumoniae. Cold agglutinins are IgM antibodies directed against the glycolipid antigens of M. pneumoniae and cross-react with the "I" antigen of the erythrocyte at low temperatures. High levels are seen in about 50-60% of untreated patients with M. pneumoniae pneumonia. In a patient strongly suspected of having M. pneumoniae infection, the presence of cold agglutinins with a significant titer is reasonably supportive evidence for a diagnosis. The cold agglutinins appear within a week of M. pneumoniae infection, peak in 12-25 days, and disappear in 2 months. Even though non-specific and crude, a positive cold agglutination test is helpful in diagnosing M. pneumoniae pneumonia in adults. The absence of cold agglutinins does not rule out M. pneumoniae infection. A significant level of cold agglutinins is not seen in infections by other microorganisms listed.

Presently used laboratory diagnostic tests for diagnosis of atypical pneumonia caused by M. pneumoniae include M. pneumoniae cultures, antigen detection tests, polymerase chain reaction (PCR), demonstration of specific antibodies by complement fixation (CF) test, enzyme-linked immunoassay (EIA), and indirect immunofluorescence assay. PCR is very useful for detection of M. pneumoniae in clinical specimens. PCR assays targeting different regions of the genome have been developed. The assays are rapid and can also detect non-viable mycoplasma in tissues processed for histological examination.

Serological tests detect surface antigens of M. pneumoniae. Glycolipids are detected by CF test. Proteins are detected by ELISA. Simultaneous testing of paired sera collected 2-3 weeks apart for IgM and IgG antibodies and demonstration of 4-fold or greater increase in antibody titer is diagnostic. An increase in titer indicates current or recent infection. ELISA tests with good specificity using purified recombinant protein antigens have been developed. Though various methods have been used, EIAs are the most widely used commercial mycoplasma serology tests in the United States.

Chlamydia pneumoniae is another important agent of community-acquired atypical pneumonia. This is an obligate intracellular organism capable of persistent latent infection. Most cases of pneumonia are mild and the clinical spectrum resembles M. pneumoniae infection. Diagnosis of C. pneumoniae pneumonia is by antigen detection using EIA, direct immunofluorescence, or molecular methods. The organism grows poorly on cell cultures. Serodiagnosis by CF, ELISA, or micro-immunofluorescence is helpful in diagnosis. A cold agglutination test is negative.

Legionella pneumophila is an aerobic, fastidious, Gram-negative bacillus associated with community-acquired pneumonia. Several serotypes have been identified. Type 1 is associated with most human cases of pneumonia. Outbreaks of infections have been associated with condensers, cooling towers, respiratory therapy equipment, showers, whirlpools, and water faucets. Among community-acquired pneumonia due to various causes, Legionnaire's disease is the most severe form. Laboratory diagnosis is by demonstration of the organisms in clinical specimens such as sputum, bronchial lavage, lung biopsy by fluorescent antibody test, isolation of the pathogen by culture on specialized media, by urinary legionella antigen test, and by demonstration of specific antibodies in serum by ELISA or indirect fluorescent assay. Cold agglutinins are not a feature of this infection.

Coxiella burnetii belongs to the Rickettsial group of organisms. It causes Q fever, a zoonotic disease transmitted by ticks among domestic livestock and other animals. It is an obligate intracellular pathogen primarily affecting monocyte-macrophage cells and occurs as small rods 0.2-0.4 x 0.4-1 micron. Though ticks are important vectors and transmit the infection among animals, they do not seem to be important in the transmission of human infection. Human infection occurs mainly by inhalation of dust or aerosols containing the organisms or occasionally by drinking milk from infected animals.

Chlamydia psittaci causes psittacosis, a zoonotic disease acquired from birds. Infection can produce a wide spectrum of diseases ranging from mild influenza-like illness to fatal pneumonia. Septicemia, meningoencephalitis, endocarditis, and typhoid-like conditions are other clinical manifestations of C. psittaci infection. Inhalation of infected dried bird excreta is the common mode of infection. Human infections are mostly occupational and seen in poultry workers, pet shop owners, and veterinarians. From clinical samples of sputum, blood, or lung tissue, C. psittaci can be isolated using tissue cultures, eggs, or mice. Detection of IgM and IgG antibodies by microimmunofluorescence is helpful for diagnosis. Antigen detection methods using direct fluorescent antibody test or by immunoassay and molecular diagnostic methods are available in reference laboratories.
Correct answer:
Mebendazole (Vermox)

Explanation
This patient has an intestinal infection with Enterobium vermicularis, commonly known as pinworms. This most commonly occurs in children, and the possible symptoms include perianal or perineal itching, dysuria, insomnia, restless sleep, and vulvovaginitis. Children complain about the symptoms, especially the itching, more during the night. The physical examination should include inspection of the perianal area, and may even include a digital rectal examination or an anal swab. Microscopic examination will reveal ova, but the female worm may also be visualized. Parents can test at home by placing clear tape over the child's perianal skin during the early morning. The treatment for pinworms should include either mebendazole (Vermox), albendazole, or pyrantel pamoate, which are all anti-worm medications.

Cefdinir is a cephalosporin that can be used to treat various bacterial infections, specifically otitis media, tonsillitis, sinusitis, and various skin infections in children; however, it is not effective against worms.

In the oral form, miconazole is an antifungal used as an oral buccal tablet for the treatment of oropharyngeal candidiasis in adults. Alternatively, it can also be found in creams used to treat candidiasis of the diaper area; however, it is not effective against worms.

Doxycycline is a tetracycline antibiotic that is usually not used in pediatrics, but can treat various bacterial infections in adults. Severe acne, sexually transmitted diseases, and urinary tract infections (usually complicated) can be treated with doxycycline. It would not be effective in the treatment of worms.

Metronidazole can be given orally or intraveneously to treat susceptible anaerobic infections, including those occurring in the gastrointestinal system, on the skin, or in the lower respiratory tract. It would not be effective against worms.
Correct answer:
Giardia lamblia

Explanation
Despite vast improvements in sanitation, food-borne illnesses remain a fairly common occurrence. Prompt laboratory investigation is required in order to establish the diagnosis. This usually only occurs when a relatively large number of individuals simultaneously experience a similar constellation of symptoms after having consumed a common food source. Therefore, many cases of food-borne illness often go undiagnosed. Several infectious sources are associated with food-borne illness. The clinical symptoms associated with them demonstrate significant overlap, yet several of the most common causes have distinguishing features.

Giardia lambliais a protozoon that causes upper intestinal enteritis marked by fatigue, chronic diarrhea, steatorrhea, colicky abdominal pain, and bloating. Infection can occur with ingestion of a single cyst, and symptoms generally appear within 1 week of exposure. Fecal contamination of drinking water is a common source of infection, as is person-to-person infection via hand-to-mouth contact with the feces of an infected individual. This method has caused outbreaks to occur in institutional facilities such as day care centers. Diagnosis of Giardia lamblia can be made by visualization of trophozoites or cysts in appropriately prepared fecal specimens.

Staphylococcus aureus produces illness indirectly via a specific enterotoxin. Patients present with rapid onset of symptoms, usually within 30-60 minutes of ingestion. Patients typically experience nausea and cramps followed by vomiting. Duration of symptoms is short, usually 24-48 hours. Since humans are the principal reservoir for Staphylococcus, uncooked foods that require extensive handling, such as salads, eggs, dressings and sandwich meat, are the most common sources. Staphylococcus aureus also causes dermatologic lesions, such as pustules and abscesses; when present on the skin of food handlers, they can be a source of contamination. In addition, Staphylococcus aureus is present in cows; therefore, milk and cheese products that are not adequately refrigerated can also cause illness.

Bacillus cereus is another organism that causes illness via the production of enterotoxins. 2 enterotoxins are produced by these spore-forming bacteria, 1 that is heat stable and another that is inactivated by heat (heat labile). The heat stable species primarily causes vomiting, whereas the heat labile form results predominantly in diarrhea. Intoxication caused by Bacillus cereus is most commonly associated with foods - classically rice - that have been reheated after having been left at room temperature. Illness usually occurs within a few hours of ingestion and usually resolves within 24 hours.

Clostridium perfringens is also a toxin-producing organism. Cramping and diarrhea are the most common symptoms of illness caused by C. perfringens. Nausea also occurs, but vomiting is rare. Inadequately heated meat products are the most common source. Onset of symptoms occurs within 12 hours of ingestion, and symptoms usually abate in a day.

Although often asymptomatic, infection with the Entamoeba histolytica protozoan can produce a host of intestinal syndromes, the most severe of which is acute dysentery marked by fever, chills, and bloody or mucoid diarrhea. Less severe colitis, indistinguishable from other causes of inflammatory bowel disease, can also occur, making the diagnosis of amebiasis difficult. In addition to intestinal illness, Entamoeba histolytica can also cause liver abscesses. As with giardiasis, fecally contaminated food or water is the most common method of transmission.
Correct answer:
Cervical cancer

Explanation
The majority of cervical cancers (approximately 90%) contain human papilloma virus DNA, usually of type 16 or 18. Human papilloma viruses are members of the family Papovaviridae and have predilection for the skin and mucous membranes. Human papilloma viruses are associated with warts, respiratory papillomas, oral infections, and genital infections. Human papilloma viral infection may progress over a period of years through the various stages of cervical intraepithelial neoplasia to invasive squamous carcinoma.

Hepatitis B virus (HBV) is a human carcinogen associated with hepatocellular carcinoma. The incidence of hepatocellular carcinoma is higher in a person who becomes infected with HBV earlier in life. The pattern observed is: person develops chronic hepatitis leading to cirrhosis of the liver and eventually to liver cancer 20-50 years post-infection. The genome of HBV is small and comprises a small, circular, partially double-stranded DNA molecule. HBV replicates in hepatocyte and involves RNA intermediate and a virus coded reverse transcriptase. HBV can become integrated into the cellular chromosome during chronic infection, and it may promote genetic instability in the cell.

Dengue fever virus and Powassan virus are members of the family Flaviviridae. Flaviviruses are enveloped viruses with icosahedral symmetry. The genome consists of a linear single-stranded RNA molecule, and replication occurs in the cytoplasm. Dengue fever virus is transmitted by the mosquito and is associated with bone break fever and dengue shock syndrome. Bone break fever is characterized by headache, myalgia, arthralgia, and rash. Secondary exposure can result in dengue shock syndrome, and it is characterized by gastrointestinal hemorrhage.

Herpes simplex virus type 1 (HSV-1) is a member of the Herpesviridae family and consists of a double-stranded DNA genome. Primary infection with HSV-1 mostly involves the mouth and/or throat. Gingivostomatitis is a classic clinical presentation of HSV-1 infection. It is characterized by formation of vesicles on the mouth and gums, which rupture to become ulcers.

Coxsackievirus type A and coxsackievirus type B are members of the Picornaviridae family. Picornaviruses are naked viruses with an icosahedral nucleocapsid. The genome consists of single molecule of single stranded RNA. Coxsackievirus type A is associated with herpangina, which is commonly seen in children. Herpangina is a severe febrile pharyngitis characterized by vesicles or nodules primarily on the soft palate.
Correct answer:
Tetanus vaccine, TIG (tetanus immune globulin), as well as cleaning and debriding the wound

Explanation
The correct response is Tetanus vaccine, TIG (tetanus immune globulin), as well as cleaning and debriding the wound.

Any sort of wound, especially soil-contaminated wounds, should be assessed for tetanus prophylaxis. When trauma occurs, the wound should be cleaned well and necessary debridement should be done to remove the dead and necrotic tissues; this prevents anaerobic bacteria growth. However, disinfectants will not kill the spores; therefore, vaccination is necessary in order to inactivate the spores. For grossly contaminated deep wounds, vaccination is necessary if the last booster was given more than 5 years ago. Also, TIG should be given to inactivate the toxin. The administration of both immune globulins and tetanus toxoid (at different sites of body) is an example of passive-active immunity.

For minor wounds, cleaning will be sufficient only if the tetanus vaccine was given less than 10 years ago. If the vaccination history is unknown or not completed, the vaccine should be given.

Clostridium tetani is an anaerobic, Gram-positive, spore-forming rod; the main reservoirs are soil and stool. Deep wounds create an anaerobic environment and increase the chance of C. tetani growth. Spores germinate in the tissues, producing an exotoxin called tetanospasmin. This toxin is carried intra-axonally to the CNS, binds the ganglioside receptors, and blocks the release of inhibitory mediators (glycine and GABA) at spinal synapses. Excitatory neurons become unopposed and cause extreme muscle spasms.

The tetanus vaccine (toxoid vaccine = formaldehyde-treated toxin) made a big breakthrough in controlling tetanus cases worldwide. Tetanus is still a problem in developing countries; however, in the United States, only 100 - 150 cases are seen per year. The vaccine is given at the age of 2 months, 4 months, 6 months, 18 months, and 5 years, in combination with diphtheria and pertussis (as DTP). A booster is given at the age of 14 - 16 years and every 10 years thereafter. Penicillin or metronidazole can be given prophylactically for grossly contaminated wounds.
Correct answer:
Haemophilus influenzae

Explanation
Haemophilus influenzae is a Gram-negative coccobacillus that requires the presence of hemin (X factor), nicotinamide adenine dinucleotide (V factor), 5% CO2, and a temperature of 35°C for growth. Growth on routinely used artificial media is restricted to chocolate agar, which has the necessary growth factors available for the organism to utilize. The organism can cause a variety of diseases (e.g., meningitis, lower respiratory infections, glossitis, abscesses, and pyogenic arthritis). In cases of invasive disease, the patients often have underlying factors that predispose them to infection. Biliary cirrhosis, splenectomy, multiple myeloma, and immunoglobulin subclass deficiencies can predispose individuals to these infections. Ampicillin is the drug of choice.

Kingella kingae is a Gram-negative diplococci that is oxidase-positive, catalase-positive, ferments glucose, indole-negative, nitrate-negative, and urease-negative. The organism will grow on chocolate and blood agar media, but not on MacConkey agar media. The organism has been isolated from mucous membranes, blood cultures, and bone or joint-associated sites. In most clinical reports, the organism has been isolated as a cause of septic arthritis in children. The antimicrobial therapy of choice is a beta-lactam alone, or in combination with an aminoglycoside.

Streptobacillus moniliformis is a Gram-negative bacillus that is present as long, curved filaments intertwined with bulbous swellings in the central position. They are catalase and oxidase-negative. The organisms are fastidious, and generally require 48 hours of incubation at 35°C in a 5% CO2 atmosphere. Growth on artificial media occurs on blood agar, but not MacConkey agar. The organism is the causative agent of rat-bite fever. Usually, a history of a bite or contact with a rodent is suggestive of an etiologic diagnosis of Streptococcus moniliformis. Penicillin is the antibiotic of choice when treating rat-bite fever.

Neisseria gonorrhoeae is an aerobic Gram-negative diplococci; it is shaped like a kidney bean. The organism is oxidase-positive, glucose-positive, and negative for ONPG, sucrose, and maltose. It is 1 of the most common sexually transmitted diseases, and it causes a host of infections (e.g., genital, pharyngeal, anorectal, pelvic inflammatory disease, perihepatitis, and disseminated gonococcal infection). Disseminated gonococcal infections can result in an arthritis-dermatitis syndrome; this syndrome produces a migratory polyarthralgia that primarily involves the knees, elbows, and more distal joints. 75% of these patients develop a characteristic dermatitis that consists of papules and pustules, often with a hemorrhagic component. In cases of disseminated gonococcus, ceftriaxone is the initial drug of choice.

Streptococcus pyogenes is a Gram-positive cocci that is catalase-negative, beta-hemolytic on blood agar, and has a Lancefield grouping of A. The organism can cause an infection called necrotizing fasciitis (streptococcal gangrene), pharyngitis, rheumatic fever, and wound infections. The antimicrobial of choice in treating Streptococcus pyogenes infections is penicillin G.

Staphylococcus aureus is a Gram-positive cocci that is catalase-positive and coagulase-positive. On Gram stain, it morphologically appears in clusters. The organism is usually beta-hemolytic on 5% sheep blood agar, and the colonies have a yellowish color. Staphylococcus aureus can cause a variety of infections (e.g., abscesses, bone infections, pneumonia, toxic shock syndrome, conjunctivitis, and carbuncles). Bone infections are usually due to the introduction of the organism through injury or invasive procedures.
Correct answer:
Pneumocystis pneumonia

Explanation
Whenever a young patient presents with fever, progressive exertional dyspnea, hypoxia, and loss of weight, the possibility of Pneumocystis jiroveci pneumonia complicating acquired immunodeficiency syndrome (AIDS) should be considered, especially when diffuse interstitial infiltration (or patchy shadows) are found on chest radiological study. The history of a homosexual encounter favors this diagnosis. This should be followed by tests to confirm HIV.

The increased alveolar-arterial O2 gradient indicates severe respiratory dysfunction. Bronchoalveolar lavage with lung biopsy is an appropriate early step in his evaluation. Finding pneumocystic cysts in the alveolar lavage is a confirmatory diagnosis for Pneumocystis jiroveci pneumonia. Treatment is based on the alveolar-arterial O2 gradient, which is considered mild when the value is less than 35 mm Hg, moderate when it is 35-45 mm Hg, and severe disease when more than 45 mm Hg.

The mainstay of treatment is given intravenously or orally. Combined therapy of trimethoprim-sulfamethoxazole and corticosteroids is necessary in the treatment of a severe case of pneumocystis in AIDS. Administration of corticosteroids helps to prevent respiratory failure and death in AIDS patients.

When Pneumocystis jiroveci Pneumonia is found in the absence of underlying immunosuppression from malignancy or drug, the patient fulfills the definition of AIDS. The laboratory findings are not suggestive of tuberculosis, legionella pneumonia, lung cancer, or syphilis.
Correct answer:
Secondary syphilis

Explanation
Secondary syphilis presents with mucocutaneous lesions and constitutional symptoms that can mimic several different disorders, and thus clinicians need a very high index of suspicion to consider syphilis as a diagnosis. Syphilis is a sexually transmitted disease that is caused by infection with the spirochete Treponema pallidum.

Acquired syphilis begins as T. Pallidum enters through the mucous membranes, generally after sexual contact, and the spirochete infects the regional lymph nodes. It then rapidly spreads throughout the body. The primary stage of syphilis is characterized by a primary lesion known as the chancre. It presents as a painless ulcer with regional lymphadenopathy and usually appears about 3 to 4 weeks after initial exposure..

The next stage, secondary syphilis, is characterized by the development of cutaneous rashes and mild constitutional symptoms. The cutaneous manifestations typically include a symmetric, papular, non-pruritic rash along the flexor, palmar, and plantar surfaces. The rash appears reddish-pink in Caucasian patients and more darkly pigmented in African American patients. Additionally secondary syphilis often presents with eroding lesions on the mucous membranes, in the mouth, vagina, penis, or rectum. They appear as grayish-white patches with a red center.

The cutaneous rashes of secondary syphilis appear about 3 to 6 weeks after the end of the primary stage, and they are most pronounced after 3 to 4 months. This stage will resolve spontaneously, although in pigmented individuals some of areas of the rash may have residual hyperpigmentation or depigmentation.

Secondary syphilis often has mild constitutional symptoms as seen in this patient. Mild anemia, hyperbilirubinemia, and albuminuria may be present as well.

Tertiary or late stage syphilis is characterized by involvement of the nervous and cardiovascular systems. Tertiary syphilis may manifest years after the initial infection, and presentations include neurosyphilis (tabes dorsalis, meningitis, and dementia), thoracic aneurysm, osteitis, or the gummas of benign tertiary syphilis. Tertiary syphilis is uncommon.

Secondary syphilis is treated with penicillin. All sexual contacts from the past year should be examined and treated, as well as educated as to their infectivity and that of their sexual partners. This patient has a presentation that is classic for secondary syphilis. Although no sexual history or serologic tests for syphilis are included in the history, a high index of suspicion for this disease will lead to the correct diagnosis.

Rocky Mountain spotted fever can have a similar rash, although patients are usually febrile, with a more acute course, and you would not expect lesions in the mouth. Rocky Mountain spotted fever is caused by Rickettsia rickettsii, and is transmitted by ticks. Hand-foot-and-mouth disease is an acute infection caused by an enterovirus, and it typically affects only children. The oral lesions of hand-foot-and-mouth disease are vesicles that ulcerate, and they are very painful. Influenza and streptococcal infections are not likely to produce the cutaneous findings seen in this patient.
Correct answer:
Begin oral fluconazole immediately

Explanation
This patient has a candidal infection. Of the antifungal therapies available, fluconazole is generally better tolerated than amphotericin B. The side effects are rare and include nausea, vomiting, rash, abdominal pain, and hepatotoxicity. It has almost equal bioavailability in the oral and intravenous routes. This patient has no underlying gastrointestinal disorder and would benefit from getting the oral fluconazole.

The normal locations for Candida are the gastrointestinal tract, oropharynx, and vagina. The most common site to isolate Candida in hospitalized patients is in urine. The morbidity rate of candidiasis with symptoms (once blood borne) is high in hospitalized patients. This becomes more serious in the presence of an abdominal abscess, endocarditis, endophthalmitis (seen as cotton-wool exudates on funduscopic exam), myocarditis, esophagitis, pneumonia, peritonitis, and thrush. Candida can also be indicated by fever despite antibiotic therapy, hypotension, leukocytosis, colonization in a wound, or post-operative surgical site and suppurative phlebitis. Thrush in this patient is often a marker of HIV, overzealous use of antibiotics, or steroids.

Risk factors for candidiasis include using more than 3 antibiotics simultaneously, using broad-spectrum antibiotics for longer than 4 days, a stay of longer than 4 days in the intensive care unit, the use of mechanical ventilation for longer than 48 hours, abdominal surgery, neutropenia, diabetes mellitus, and immunosuppression. In cancer patients, thrush is often a marker for esophageal candidiasis. The presence of Candida in this patient cannot be ignored due to the potential for prolonged hospital stay and subsequent high health costs; there is rapid progression of the organism once blood borne; there is also high mortality rate.

Once Candida is suspected, specimen cultures should be obtained from the oropharynx, sputum, stool, urine, and surgical sites. Antifungal therapy needs to be initiated immediately. Once the culture and sensitivities are available, then the therapy can be adjusted. One should not wait for the culture results before starting antibiotic therapy.

Amphotericin B has acute toxicity, and because of this it often needs to be stopped prematurely. Important side effects include fever, rigors, hypotension, anorexia, and tachypnea. A chronic side effect is renal toxicity. Since the patient has diabetic nephropathy, it should not be administered to him.
Correct answer:
Varicella-zoster immune globulin

Explanation
If birth is 2 - 3 weeks after onset of clinical varicella, it is less likely the neonatal infection will be serious. However, if birth is <1 week after, or up to 2 days before maternal varicella, neonatal chickenpox is likely to be severe. In this case, infants should be passively immunized with varicella-zoster immune globulin (VZIG). All premature infants should receive VZIG if maternal varicella is present, regardless of the timing of infection.

Risk of varicella transmission by breast-feeding is unknown. Perinatally acquired varicella may be life-threatening. Acyclovir can be used to treat varicella infection in neonates. Giving birth within 1 week before or after the mother has clinical varicella may result in neonatal disease, which is often severe. Varicella transmission may be intrauterine or perinatal. Maternal anti-VZV antibody protects the fetus; accordingly, the severity of neonatal varicella reflects the interval between parturition and maternal onset of chickenpox.

Varicella (chicken pox) is a childhood disease caused by varicella-zoster virus (VZV), a herpes virus. Although it is thought to be a mild disease, there are approximately 10,000 varicella-related hospitalizations and 100 deaths annually in the United States. In children, secondary skin infections are the most common complication of varicella. Children with chickenpox have a 3-fold increase in risk for group-A streptococcal infections and sequelae, including necrotizing fasciitis and toxic shock syndrome. Central nervous system complications in children include cerebellar ataxia (1 in 4,000) and encephalitis (1 in 50,000). Varicella is more serious in adults than in children; adults represent 5% of cases and 45% of deaths due to VZV. Hospitalization for varicella among adults is most often a result of varicella pneumonia. Typically viral, this complication occurs in about 15% of healthy adults who contract varicella. In immunocompromised individuals, varicella may represent a life-threatening illness. Varicella is frequently an initial presenting infection in people with HIV disease.

About 25% of pregnant women who contract varicella will have an infected fetus, and up to 2% of infected fetuses are clinically affected. Congenital varicella syndrome is a serious condition because VZV is teratogenic. The greatest risk occurs during development of innervation of the limbs and eyes (weeks 8 - 20). The benefit of VZIG in preventing fetopathy is unknown, as is the safety and efficacy of maternal administration of antiviral agents such as acyclovir.

Varicella can be prevented with a vaccine that consists of an attenuated strain of VZV. Varicella immunization is recommended for all children 12 months to 18 years of age regardless of varicella history, and for all susceptible children 19 months to 12 years old who have not been immunized previously. Adults may also be vaccinated. HIV-infected children who are asymptomatic and have no evidence of immunosuppression (>25% CD4+ T-cells) should receive the varicella vaccine at age 12 - 15 months, or older.
Correct answer:
Paramyxovirus

Explanation The patient is suffering from rubeola/measles, which is caused by a paramyxovirus1. It is characterized by truncal rash, centrally distributed, which usually starts at the hairline and moves down the body, sparing the palms and soles. It begins as discrete erythematous lesions that become confluent as the rash spreads1. Koplik's spots (1-2mm white or blue lesions surrounded by an erythematous halo on the buccal mucosa) are pathognomonic for measles and are generally seen during the first 2 days of infection1. This patient has both the typical rash and Koplik's spots, which help make the diagnosis of measles.

Togavirus causes rubella1. The rash of rubella spreads from the hairline downwards, but unlike that of measles, the rubella rash tends to clear from originally affected areas as it migrates. In addition, it may be pruritic1. Forchheimer spots (palatal petechiae) may develop and are nonspecific1.

Human parvovirus B19 causes erythema infectiosum1. It primarily affects children 3-12 years old1. The rash associated with this illness develops after resolution of a fever and appears as bright, blanchable erythema on the cheeks (slapped cheeks) and perioral pallor1. A more diffuse rash (often pruritic) then appears on the trunk and rapidly develops into lacy reticular eruptions that wax and wane (especially with temperature changes) over several weeks1.

Human herpes virus 6 causes roseola/exanthem subitum1. A diffuse maculopapular eruption develops over the trunk and neck, then resolves within 2 days. The rash follows resolution of fever1. It appears as 2-3mm macules and papules initially on the trunk and sometimes on the extremities (sparing the face), which fade within 2 days1.

Varicella-zoster virus causes chicken pox characterized by macules evolving into papules and vesicles on an erythematous base. Lesions are pruritic and appear in crops1.
Correct answer:
Testing for serum antibodies

Explanation
Testing for serum antibodies helps to confirm a clinical diagnosis of Lyme disease. Lyme arthritis is one of the common manifestations of Lyme disease, a multi-system disease caused by Borrelia burgdorferi and a few other Borrelia species of spirochetes. In the United States, Lyme disease is the most common vector-borne disease caused by B. burgdorferi. Lyme disease is named after Lyme, Connecticut, where the first cases were detected. The main vector is Ixodes scapularis, a deer tick. Human infections follow as a result of a bite from adult or nymphal ticks infected with the spirochete. The most common reservoir of B. burgdorferi is white-footed mice; nymphal Ixodes scapularis feed on these small mammals. The infected mice maintain a persistent asymptomatic spirochetemia for life. The incidence of Lyme disease is reported to be on the increase in several states in the United States.

Early Lyme disease is characterized by a skin lesion following a tick bite; this is known as erythema migrans. Dissemination occurs days or months after the tick bite, leading to musculoskeletal, cutaneous, cardiac or neurological manifestations, meningitis, and joint involvement. Several months to years after the infecting tick-bite, approximately 60% of untreated patients develop intermittent bouts of joint pain and swelling; large joints are mostly affected. In the United States, Lyme arthritis is reported as the most common late manifestation of Lyme disease, and it may present without a history of exposure or any other concomitant symptoms.

B. burgdorferi has a complex antigenic composition. Differential expression of its surface proteins in the mammalian host is thought to help the organism evade a host immune response and cause persistent infection.

Serological testing for B. burgdorferi antibodies is indicated for a diagnosis in patients with a characteristic clinical picture of Lyme disease, except in those with erythema migrans; antibodies may not be at a detectable level. To improve the accuracy of serological testing, two-tier testing is recommended. Detection of IgG antibodies against B. burgdorferi by this method helps to confirm the diagnosis of Lyme arthritis. Serum is tested first by enzyme-linked immunosorbent assay (ELISA); if the result is positive or equivocal, it is tested by a more specific Western blot to corroborate the result of the first test. If the ELISA test is negative, no further testing is indicated. Whole-cell sonicates of B. burgdorferi are commonly used as the source of antigen in ELISA. The ELISA test for IgG antibodies is invariably positive in late disease (e.g. arthritis). Interpretation is done according to the criteria of the Centers of Disease Control and Prevention. A positive serology in the absence of clinical features cannot be considered a marker for diagnosis. False positivity due to cross-reactivity can occur in other conditions (e.g., relapsing fever, syphilis, and rheumatoid arthritis). In endemic areas, normal individuals may have serum antibodies. Serology done in the absence of a clinical suspicion of Lyme disease may lead to misdiagnosis.

Lyme arthritis usually responds to antibiotic therapy. Oral doxycycline, tetracycline, or amoxicillin can be used for treating Lyme arthritis in adults. Amoxicillin, penicillin, or erythromycin can be used for children. Intravenous administration of cefotaxime, or ceftriaxone, is found effective in those who do not respond to oral therapy. In spite of the antibiotic therapy, some individuals develop chronic arthritis. This is observed in patients with certain HLA-DRB alleles. An autoimmune phenomenon involving antigenic mimicry between the outer surface protein OspA of B. burgdorferi and human lymphocyte-function-associated antigen-1 (LFA-1) is thought to have a role in the development of long-standing arthritis.

No human vaccine is currently available for Lyme disease. An ecological approach to the control of Lyme disease, based on the immunization of animal reservoirs, has been reported. It is suggested that successful vaccination of the reservoir population intervenes in the natural cycle of Lyme disease and helps in reducing the transmission of infection to humans.

The detection of B. burgdorferi antibodies in synovial fluid is of diagnostic significance. B. burgdorferi in fluid culture media can be observed as highly motile bacteria by dark-field and phase-contrast microscopy. Preparations stained by silver stains or fluorescent dyes can be visualized using light microscopy, but the utility of microscopic assay for the confirmation of Lyme arthritis is limited (due to the sparseness of the bacteria in clinical samples).

Barbour-Stoenner-Kelly medium (BSK II), a complex liquid medium, is used for culturing B. burgdorferi, although rarely has the bacterium been isolated from synovial fluid. The bacterium is a slow-grower and requires prolonged incubation (up to 12 weeks) before the culture can be considered negative. Culture is mostly done for research studies, and not as a routine diagnostic test in clinical practice.

B. burgdorferi DNA can be detected in the synovial fluid by a polymerase chain reaction (PCR); it has about 90% sensitivity and is more sensitive than a culture. Potential false positivity, due to contamination of the sample, is considered as a drawback for PCR assays. The test is not yet standardized and not recommended for routine diagnostic use.

Blood culture samples are only rarely positive, even in early Lyme disease (erythema migrans) and in patients with systemic symptoms of dissemination. Recent studies have shown better recovery of B. burgdorferi by culturing enough plasma from untreated patients with erythema migrans. Blood culture is not indicated for diagnosing Lyme arthritis.
Correct answer:
Chlamydia trachomatis

Explanation
Chlamydia trachomatis is an obligate intracellular parasite. It is considered the most common sexually transmitted disease. It can cause lymphogranuloma venereum, inclusion conjunctivitis, urethritis, proctitis, endometritis, pelvic inflammatory disease, ectopic pregnancy, and reactive arthritis. It can be symptomatic or asymptomatic. Discharge is a clear fluid, and the urethral discomfort is not severe. WBC content of the discharge is normally low. The organisms do not gram stain. Direct fluorescent staining of the discharge can be used to make a diagnosis, as well as DNA probe and EIA methods. Treatment is with any of the tetracycline antibiotics.

Neisseria gonorrhoeae is a Gram-negative cocci occurring in pairs and having a kidney bean shape. It is a common sexually transmitted bacterial infection. It causes a disease that is far more reactive clinically than Chlamydia trachomatis. In cases of urethritis, the patient generally is in great discomfort especially when voiding. There is a purulent discharge that if gram stained, will produce a smear containing large numbers of WBCs and Gram-negative diplococci. The presence of the gram-negative diplococci within the WBCs is diagnostic for Neisseria gonorrhoeae. It is susceptible to a wide variety of antibiotics. Previously, penicillin was the drug of choice; currently, ceftriaxone, cefixime, ciprofloxacin, or ofloxacin are more commonly used.

Herpes simplex is a virus and is sexually transmitted. It causes vesicular lesions that in the male patient usually appear on an erythematous base that can be located on the glans penis or the penile shaft. In the female, lesions may involve the vulva, perineum, buttocks, cervix, and vagina. Primary infections may be associated with fever, malaise, anorexia, and tender inguinal adenopathy. The lesions that occur can be very tender. There may be urinary retention and dysuria. Viral cultures, serological testing, and Tzanck smears can help make a definitive diagnosis.

Haemophilus ducreyi causes chancroid or soft chancre and is a sexually transmitted disease. It is a Gram-negative, cocci-bacillary-shaped organism and requires special growth requirements for isolation. The organism mimics Treponema pallidum in its clinical presentation. Dark field examination of ulcer material and serologic testing for syphilis should be performed to exclude syphilis. The chancre is painful to the touch; it is raised with a surrounding base of erythema, with the base composed of a granulation of tissue that bleeds easily upon manipulation. There is lymphadenopathy present in the groin area. Super-infections can occur; in such cases, extensive damage of the genitalia can occur.

Treponema pallidum is the causative agent of syphilis. It is a spirochete. The organism is slender, tightly coiled, unicellular, helical cells 5 - 15 um long. The initial disease produces a syphilitic ulcer or chancre. Material from this chancre can be sent to the lab for dark field microscopy where the highly motile spirochete can be observed and is diagnostic for syphilis. Serological studies, non-treponemal for screening and treponemal for confirmation, are also used to aid in the diagnosis. The syphilis chancre is painless. The disease can progress from the primary stage to secondary, latent, and late.
Correct answer:
Clostridium botulinum

Explanation
Clostridium botulinum is a Gram-positive, spore-forming bacillus that is anaerobic. The organism produces a potent paralytic neurotoxin that can be fatal. In infants, clostridium botulinum produces a disease called 'infant botulism'. The incubation period is 3 - 30 days. Signs and symptoms of infant botulism are lethargy, weakness, poor feeding, constipation, hypotonia, poor head control, and poor gag and suck reflex. The duration of the illness is variable. Foods that are implicated in the disease are honey, and home-canned vegetables and fruits. The stool, serum, and food should be tested for the presence of toxin. Testing is usually done at specialized reference laboratories. Since botulinum antitoxin is not recommended for infants, supportive care is the treatment of choice.

Campylobacter jejuni is a Gram-negative bacilli that is thermophilic and microaerophilic. The organism is oxidase-positive. The organism is a major human enteric pathogen that is equal to or greater than Salmonella and Shigella in incidence. The incubation period is 2 - 5 days, with a duration of illness of 2 - 10 days. Symptoms of Campylobacter infection include diarrhea (often bloody), cramps, and vomiting. The organism is found in raw and undercooked poultry, unpasteurized milk, and contaminated water. Supportive care is the treatment of choice; however, in severe cases, antibiotics such as erythromycin and a quinolone may be indicated. Also, Guillain-Barré syndrome can be a sequela.

Bacillus cereus is a Gram-positive, spore-forming bacillus that is aerobic. It is catalase-positive, beta-hemolytic on sheep blood agar, nitrate-positive, and VP-positive. It is a major cause of a rapidly occurring food poisoning that produces severe nausea and vomiting; occasionally, there will be diarrhea. The duration of symptoms is generally about 24 hours. The source of the bacteria is improperly refrigerated cooked and fried rice, and meats. Diagnosis is usually performed clinically; however, a laboratory diagnosis when requested should involve the analysis of stool and food specimens for culture and toxin identification.

Vibrio parahaemolyticusis a Gram-negative rod that is a halophilic (salt-requiring) vibrio. The organism is curved rather than a straight rod. It is oxidase-positive and should be cultured for selective thiosulfate citrate bile salts sucrose (TCBS) agar on which the organism appears as a distinct, opaque, green colony.. The incubation period is 2 - 48 hours, with symptoms lasting 2 - 5 days. Symptoms include watery diarrhea, abdominal cramps, nausea, and vomiting. Sources of infection include undercooked or raw seafood. Vibrio parahaemolyticus, when suspected, should be alerted to the laboratory for special media culture considerations. Supportive care is the treatment of choice. Antibiotics such as tetracyclines, doxycycline, gentamicin, and cefotaxime should be given in severe cases.

Listeria monocytogenes is a Gram-positive, non-spore-forming facultative anaerobic bacillus. It grows on blood agar well and colonies are beta-hemolytic. On Gram stain, they are frequently mistaken for diphtheroids. They exhibit tumbling motility at room temperature and are bile-esculin-positive. The gastrointestinal form of the disease has an incubation period of 9 - 48 hours. Symptoms are of variable length and include fever, muscle aches, nausea, and/or diarrhea. Sources of infection include unpasteurized or under-pasteurized milk, ready-to-eat deli meats, and hot dogs. Though gastrointestinal initially, the disease can evolve into an invasive stage in 2 - 6 weeks. Blood or cerebrospinal spinal fluid cultures are best for invasive disease. Because of asymptomatic fecal carriage, stool cultures are not usually helpful. Treatment of choice is supportive care and antibiotics. In cases of invasive disease, intravenous ampicillin, penicillin, or TMP-SMX is recommended.
Correct answer:
Neuroimaging methods

Explanation
Progressive cognitive, motor, and behavioral problems in an HIV-infected patient points to the diagnosis of AIDS dementia complex. Brain imaging is essential in the evaluation of patients with AIDS dementia complex, not only for the confirmation of the diagnosis, but also to exclude opportunistic infections, including progressive multifocal leukoencephalopathy, toxoplasmosis, tuberculosis, and cryptococcosis, as well as tumors, primary CNS lymphoma and/or the ependymal changes consistent with cytomegalovirus encephalitis. Neuroimaging in AIDS dementia complex will show cerebral, often basal ganglia atrophy, and white-matter abnormalities (described as "fluffy," "ground-glass," or even diffuse).

Formal neuropsychological tests are not diagnostically specific. In the particular clinical context, they might help you to determine whether symptoms and signs are consistent with AIDS dementia complex and determine the stage of the disease.

Electroencephalography (EEG) is the recording of spontaneous electrical activity of the brain. It is not specific and is used primarily in the diagnosis of epilepsy. Sometimes it is used in the diagnosis of coma, encephalopathies, sleep disorders, and brain death.

Cerebrospinal fluid examination is also non-specific; it might be even normal or you may find slightly elevated spinal fluid protein, IgG, oligoclonal bands, and lymphocytosis. CD4/CD8 ration reflects the ratio in blood. HIV may be isolated either directly from the CSF or in culture. CSF examination is better used in differential diagnosis rather than as a method to diagnose ADC, since CSF findings in these patients are not specific.

Although AIDS dementia complex is usually observed in the late stages of acquired immunodeficiency syndrome, when CD4+ lymphocyte counts fall below 200 cells/mL, lymphocyte counts is not diagnostic for AIDS dementia complex.
Correct answer:
Hand-foot-mouth disease

Explanation
Hand-foot-mouth disease, a childhood disease, is a rash consisting of vesicles on a reddened base. The hands and feet are the most common body parts affected. Oral ulcers or vesicles can be seen. Fever sometimes occurs with the other symptoms. Coxsackie virus is the etiologic agent of hand-foot-mouth disease. The typical time for hand-foot-mouth disease to occur is during the summer and fall.

Prior to the onset of the rash of measles, there is a fever, an upper respiratory infection, and Koplik's spots. Koplik's spots are blue-gray spots that can be seen in the mouth. The rash is a maculopapular rash that may become confluent. Typically, the rash begins on the face and moves downward and outward over the whole body. The rash can go to the hands and feet. A patient with measles can have associated cough, adenopathy, and high fever. Winter and spring are the typical times of year for measles to occur.

Kawasaki disease is a disease that occurs in children. There is a high fever before the onset of the rash. The rash seen with Kawasaki disease is erythematous with desquamation. The entire body can be affected by the rash. Winter and spring are the typical times of year for Kawasaki disease to occur.

Toxic shock syndrome is caused by a toxin produced by Staphylococcus aureus. There is accompanying high fever and hypotension. There is no predilection for a particular season.

Rocky Mountain spotted fever is transmitted by ticks. With Rocky Mountain spotted fever there is a fever, headache, and malaise. The wrist, ankles, palms of the hands, and soles of the feet are initially affected. The trunk can also be affected. Rocky Mountain spotted fever is caused by Rickettsia rickettsii. April through September is the typical time frame for Rocky Mountain spotted fever to occur.
Correct answer:
Activation from latency

Explanation
The symptoms in this are most consistent with shingles, which is caused by the herpes zoster virus. Herpes zoster virus is identical to the varicella virus, which causes chickenpox. Exposure to the varicella virus results in the establishment of a latent state in many individuals. The virus may remain dormant for many years before being activated and expressed as a different disease, shingles. Each year, over 300,000 individuals experience severe episodes of shingles.

There are numerous factors that have been attributed to the reactivation of the herpes zoster virus. Exposure to sunlight, chemotherapy, immunosuppression, menstrual cycle changes, trauma, depression, and anxiety are but a few of the factors reported to induce the expression of shingles. Rash-like lesions associated with each episode range from undetectable to severe. Scratching can cause secondary bacterial infections, which exacerbate the situation.

Shingles affects a specific dermatome (portion of the body innervated by a segmental sensory dorsal root ganglion). Fluid recovered from the lesions contains active virus, which is capable of infecting unexposed individuals. The patient rarely autoinfects with new dermatomal presentation. Both humoral and cell-mediated immune responses restrict the spread of the virus to new body sites; however, since it is sequestered in protected ganglia, the responses are unable to eradicate the virus from the body. Interferon may stabilize the infection.

Current treatments do not eliminate the infection; they only reduce the severity of the episode. Hyperimmune globulin is effective in suppressing varicella infections in cases of known exposure. Immunosuppressed individuals are at risk from varicella; therefore, they would benefit from passive immunization. The attenuated chickenpox (herpes zoster) vaccine, first introduced in 1995, is relatively safe and effective. Prior to the introduction if this vaccine, over 12,000 people were hospitalized annually due to severe cases of chickenpox.
Correct answer:
Virus replication

Explanation
All pregnant HIV-infected patients beyond 14 weeks' gestation should be on a highly active antiretroviral therapy (HART) regimen. With cesarean delivery and appropriate antiretroviral therapy, risk of transmission of HIV to the newborn is less than 1%; the risk would be 25% without such a treatment. Zidovudine is the only anti-HIV drug that is fully approved for use during pregnancy. It is inhibits HIV's reverse transcriptase and is placed within the viral DNA. When placed in the viral DNA by the reverse transcriptase, transcription of the viral genes is inhibited. This prevents virus replication. Other drugs that belong to this group (abacavir, emtricitabine, didanosine, zalcitabine, lamivudine, tenofovir, reverset, and stavudine) are not approved because of side effects.

Protease inhibitors (amprenavir, atazanavir, fosamprenavir, ritonavir, indinavir, nelfinavir, saquinavir, and tipranavir) inhibit the retroviral protease from cleaving the viral proteins. HIV produces its own proteases that play role in the production of infective viral particles by cleaving viral proteins to sizes of a mature viral particle (viral assembly). Protease inhibitors inhibit proteases from cleaving the viral proteins; in doing so, they reduce the spread of the virus to other uninfected cells. They are not approved in pregnancy because of their serious side effects.

Enfuvirtide interferes with the viral gp41 protein and prevents fusion of HIV with the host cell. It is used in combination therapy with other antiretrovirals when all other treatments have failed.

Maraviroc and other CCR5 entry inhibitors act on the human T-cell, changing it in such a way that HIV is unable to bind and therefore continue the replication process. They interfere with the host immune system and cause serious side effects; therefore, they are not approved in pregnancy.

Integrase inhibitors, like raltegravir, inhibit the enzyme that integrates HIV genetic material host. Since the integration is a distinct step in HIV life cycle, integrase inhibitors may be taken in combination with other HIV drugs to minimize viral drugs resistance. They are also useful in the case of the resistance to other drugs. Due to their adverse effects, they are not recommended in pregnancy.
Correct answer:
Histoplasmosis

Explanation
Histoplasmosis is a chronic respiratory infection caused by inhaling the spores of the fungus Histoplasma capsulatum, which is found in bird and bat droppings common along river valleys. Most cases are mild or asymptomatic. Risk factors include travel or residence in central/eastern United States or South America, pre-existing COPD (chronic obstructive pulmonary disease), and environmental or occupational exposure to the droppings of chickens, bats, and blackbirds. Immunocompromised people are also at risk. Symptoms include fever, chills, cough (with mucus or pus), skin lesions, and joint stiffness. The associated skin lesion usually presents as a lesion on the mouth or inner cheek as a papule; it may ulcerate. Tests include chest X-ray, sputum culture, (invasive) open lung biopsy, bronchoscopy (with or without transtracheal biopsy), histoplasma complement fixation titer, and CBC. The recommended first-line outpatient treatment is oral itraconazole.

Acute pulmonary eosinophilia is a self-limiting inflammation of the lungs associated with the infiltration of eosinophils in the lungs and blood. The etiology includes exposure to various drugs, parasitic infestation (especially ascariasis in children), nickel exposure, recent blood transfusion, or lymphangiogram. Symptoms may include general malaise, loss of appetite, fever (greater than 2 to 3 days), productive cough (mucoid sputum), chest pain, shortness of breath, wheezing, rapid respiratory rate, headache, and muscle pain. Tests include auscultation of the lungs (revealing fluid), bronchoscopy (showing hypersensitivity reaction), open lung biopsy (invasive way to show hypersensitivity reaction), CBC (increased white blood cell count, particularly eosinophils), sputum smear (KOH test), and chest X-ray. If a cause is found, therapy consists of removing the offending drug or treating the infection with antibiotic therapy. If no cause is found, steroid therapy is given.

Pulmonary actinomycosis is an infection caused by Actinomyces israelii or actinomycete bacteria that causes disease of the chest, mouth, jaw, and pelvis. The bacterium is in the normal flora of the mouth and gastrointestinal tract of humans. Symptoms include lethargy, weight loss, fever, productive cough, draining sinuses, night sweats, shortness of breath, and chest pain. Poor dental hygiene and a dental abscess may predispose it to facial lesions. In the chest, it results in cavities in the lung and pleural effusion, which may spread through the chest wall and produce sinuses. Tests include a CBC showing anemia, chest X-ray, culture of specific tissue, and bronchoscopy with culture. The goal of treatment is to control infection. Long-term treatment with penicillin or an alternative is necessary to ensure a cure. Surgical drainage of the pleural effusion and surgical resection of lung lesions may be necessary to control the infection.

Acute coccidioidomycosis is a disease caused by breathing in a fungus found in the soil in certain parts of the southwestern United States, Mexico, and Central and South America. Dark-skinned people and people with a weak immune system will have more serious infections. Infection is caused by breathing in the spores of a fungus (Coccidioides immitis) found in desert regions. About 60% of infections cause no symptoms and are only recognized by a positive coccidioidin skin test. Symptoms include cough, chest pain (mild pain to severe constriction), fever, chills, night sweats, headache, muscle aches and stiffness, joint stiffness, and rash on the lower legs (erythema nodosum). Tests include sputum smear (KOH test), sputum culture, serum coccidioides complement fixation titer, CBC with differential (shows elevated eosinophils), chest X-ray, and coccidioidin or Spherulin skin test. The acute disease is almost always benign and goes away without treatment. Bed rest and the treatment of flu-like symptoms until the fever disappears may be recommended. Amphotericin B is used for progressive disease.

Pulmonary asbestosis is a respiratory disease caused by inhaling asbestos fibers; it results in pulmonary fibrosis. Asbestos-related disease includes pleural plaques (calcification), malignant (cancerous) tumors called mesotheliomas, and pleural effusion. Cigarette smoking increases the risk of developing the disease. Symptoms include shortness of breath on exertion, cough, tightness in the chest, chest pain, nail abnormalities, or clubbing of fingers. Tests include auscultation of the lungs (revealing crackling), chest X-ray, pulmonary function tests, and CT scan of the lungs. Although there is no cure, supportive treatment of symptoms includes respiratory treatments to remove secretions from the lungs by postural drainage, chest percussion, and vibration.
Correct answer:
Borrelia

Explanation
Lyme disease, first detected in Lyme, Connecticut, is a bacterial infection caused by the spirochete Borrelia burgdorferi. It is a zoonotic (animal-to-human) infection within the deer and rat populations and accidentally transmitted to man through the bite of the deer tick, Ixodes dammini. Different arthropod vectors are instrumental in the transmission of other Borrelia infections. The extremely small size (< 2 mm) of deer ticks makes them difficult to detect, compared to the larger wood tick (Dermacentor andersoni) or dog tick (D. variabilis). A large, circular, red petechial rash usually develops at the site of the tick bite. It may grow to over 10 cm in diameter and can become surrounded by an even more extensive halo of less intense rash. The bacteria may cause joint pain (arthlagia) resulting in a form of arthritis.

The primary lesion grows into an enlarged rash as the spirochete proliferates and invades the blood and lymphatic vessels. The lesion usually disappears after several weeks. Some individuals progress into a second stage of infection involving neurologic or cardiac abnormalities. An arthritic response may develop months to years after the initial infection, probably due to an autoimmune response. This is indicative of the third stage of Lyme disease.

Relapsing fever is another disease caused by bacteria of the genus Borrelia. It can be either epidemic (louse-borne) or endemic (tick-borne). Syphilis and leptospirosis are diseases also caused by different spirochetes.
Correct answer:
Chlamydia trachomatis

Explanation
The most common cause of nongonococcal urethritis is Chlamydia trachomatis.

Urethritis is an inflammation of the urethra. It is classified as either gonococcal urethritis (caused by Neisseria gonorrhoeae) or nongonococcal urethritis (caused by something other than Neisseria gonorrhoeae). Gonococcal urethritis is ruled out in this patient by the negative Gram stain results.

Chlamydia is an obligate intracellular organism. Chlamydia infections characteristically show the development of inclusion bodies. Chlamydia was once thought to be protozoa as well as viruses, but they are neither. They are bacteria in the order Chlamydiales.

Chlamydia trachomatis causes approximately half of all cases of nongonococcal urethritis in men. The other conditions caused by Chlamydia trachomatis are trachoma, inclusion conjunctivitis, and lymphogranuloma venereum. Symptoms of NGU consist of discharge from the urethra, itching, or burning associated with micturition. Diagnosis is by tissue culture, and more sensitive serological assay can be performed. Treatment with antibiotics, such as azithromycin, doxycycline, and ofloxacin, is effective. Azithromycin 2g orally as a single dose is most effective. Treatment of the sexual partner is also essential.

Chlamydia psittaci does not cause nongonococcal urethritis. Chlamydia psittaci causes a systemic illness, called psittacosis, parrot fever, or ornithosis. Psittacosis is acquired from birds.

Trichomonas vaginalis can cause nongonococcal urethritis in men but not nearly as frequently as Chlamydia trachomatis does. Trichomonas vaginalis is a protozoon. It causes trichomoniasis vaginitis, sometimes called trichomoniasis.

Mycoplasmas are the smallest organisms characterized by the lack of cell wall. They commonly inhabit the mucosa of the respiratory and the urogenital tracts, residing extracellularly. Mycoplasma hominis and M. genitalium also cause NGU but are far less common than chlamydial urethritis.
Correct answer:
Infection by Toxoplasma gondii

Explanation
The patient's history (gardening and presence of cat) and the clinical presentation are indicative of toxoplasmosis in the mother. This specifies a higher fetal susceptibility to infection by T. gondii than infection by T. pallidum, cytomegalovirus, rubella, or herpes simplex virus.

Toxoplasma gondii is a protozoan parasite that causes toxoplasmosis. Infection mainly occurs by the ingestion of food or water contaminated with oocysts shed by cats or by eating undercooked or raw meat containing tissue cysts. Primary infection (toxoplasmosis) is usually subclinical; however, in some, it manifests as cervical lymphadenopathy with low-grade fever or ocular disease. Infection that is acquired during pregnancy may cause severe fetal damage. Diagnosis of toxoplasmosis can be confirmed by direct detection of the parasite or by serological techniques. The most commonly used treatment modality, and probably the most effective, is the combination of pyrimethamine with sulfadiazine and folic acid.

Congenital toxoplasmosis occurs by vertical transmission from a recently infected pregnant woman to her fetus. Severe fetal consequences can occur when the transmission is closer to conception. The clinical manifestations include the classic triad of chorioretinitis, hydrocephalus, and intracranial calcifications. Other manifestations include anemia, jaundice, thrombocytopenia, microcephaly, convulsions, spasticity and palsies, intellectual disability, and learning disabilities.

Syphilis, caused by the spirochete T. pallidum, is a sexually transmitted disease. Rubella is a RNA virus, and congenital rubella syndrome can be prevented by measles-mumps-rubella MMR vaccination. Cytomegalovirus infection is usually asymptomatic. Symptomatic disease usually manifests as a mononucleosis syndrome in immunocompetent individuals. In herpes simplex virus (HSV) infection, HSV-1 is transmitted primarily by contact with infected saliva; HSV-2 is sexually transmitted. Congenital HSV infection results from genital HSV infection with HSV-2 type.
Correct answer:
Maculopapular rash that starts behind the ears and spreads to the face, down the trunk and extremities

Explanation
A typical measles rash is a maculopapular rash that starts behind the ears and around the forehead, spreads to the face, and then progresses cephalad, down the trunk and extremities. Pneumonia, mentioned in this case, is a common complication. Erythema infectiosum (fifth disease), also known as slapped cheek disease, begins with cheek erythema, and the maculopapular rash starts on the arms and moves down the trunk and legs.

A pruritic rash appearing initially on the trunk and then spreading peripherally is consistent with the diagnosis of varicella (chickenpox). Varicella rash, a papulovesiculopustular rash, starts with papules and then changes rapidly to the vesicles and the pustules. The lesions are usually present in several stages at the same time. Diffuse erythema of mucous membranes, palms, and soles on a child with fever should make one think about Kawasaki's disease. This is an important differential diagnosis of measles; it is a non-infectious, life-threatening, systemic vasculitis. It presents with fever, conjunctivitis, erythema of palms, soles, and mucous membranes, polymorphous rash, strawberry tongue, as well as dry, cracked lips. The most serious complications are cardiac with coronary vasculitis and aneurysm formation.

A diffuse erythematous rash with circumoral pallor surrounded by a flush face is a scarlet fever rash. This rash is more prominent on the abdomen and cutaneous folds (Pastia's lines), and it is characteristic with strawberry tongue (inflamed papilla protruding through a bright red coating).
Correct answer:
Acute Rheumatic fever

Explanation
The clinical picture is suggestive of acute rheumatic fever. Peak incident occurs between the ages of 5-15 years old, usually after a streptococcal infection of the pharynx. Signs of rheumatic fever usually commence 2-3 weeks after infection. Diagnosis is based on Jones criteria and confirmation of streptococcal infection. The presence of 2 major criteria, or 1 major and 2 minor criteria, establishes the diagnosis. Major criteria include carditis, erythema marginatum and subcutaneous nodules, Sydenham's chorea, and polyarthritis. Minor criteria include fever, polyarthralgias, reversible prolongation of the PR interval, and an elevated erythrocyte sedimentation rate or C-reactive protein.

The clinical presentation of infective endocarditis depends on the infecting organisms and the valve or valves being infected. The clinical diagnosis is based on the modified Duke criteria, which include 2 positive blood cultures for a microorganism that typically causes infective endocarditis. Positive blood cultures are not indicative in this patient.

With pericarditis, the patient does present with chest pain, but it is usually described as sharp, retrosternal with radiation to the back, and worse with deep breathing or coughing. The pain is position dependent: worse when lying flat, and improved while sitting up and leaning forward. On physical examination, the pericardial rub is pathognomonic of pericarditis, which is not present in this patient.

Kawasaki's disease is characterized by fever and 4 of the following symptoms for at least 5 days: bilateral painless, nonexudative conjunctivitis; lip and oral cavity changes; cervical lymphadenopathy > 1.5cm and usually unilateral; polymorphous exanthema; and extremity changes. 80 percent of patients are < 5 years old. Most of these symptoms are not present in this patient.

The typical clinical description of Lyme disease divides the illness into 3 stages: stage 1, flu-like symptoms and a typical skin rash; stage 2, a week to months later, Bell's palsy or meningitis; and stage 3, months to years later, arthritis. Exposure to the Ixodes tick in certain geographic locations is needed for infectivity. There is no history of tick exposure or flu-like symptoms and rash in this patient.
Correct answer:
Empiric treatment with sulfadiazine and pyrimethamine

Explanation
Opportunistic processes, such as infections and neoplasia, are often associated with CNS involvement in AIDS. Toxoplasmosis is one of the most common opportunistic infections affecting the brains of AIDS patients. Frequently, it is the presenting manifestation in patients diagnosed with AIDS. Most commonly, toxoplasmosis presents as an acute or subacute process, causing an acute mental status change, hemiparesis, headache, and seizure. CT and MRI scans show ring-enhancing lesions with mass effect. Treatment consists of sulfadiazine and pyrimethamine. Because lymphoma can mimic CNS toxoplasmosis, a biopsy may be necessary if the mass does not respond to treatment.

Cryptococcal meningitis is another common opportunistic infection seen in AIDS patients. This occurs as a meningoencephalitis due to Cryptococcus neoformans. Both toxoplasmosis and cryptococcal meningitis occur in about 5% of AIDS patients. This is usually a subacute process; it causes symptoms such as headache (most common), changes in mental status or consciousness, meningismus, fever, and occasionally seizures. Unlike toxoplasmosis, cerebral imaging is usually normal; however, hydrocephalus and basal ganglionic cryptococcomas can be seen. CSF analysis with lumbar puncture is diagnostic, with classical findings of low glucose, a paucity of inflammatory cells, and a positive India ink test (about 70% sensitive) or cryptococcal antigen (about 95% sensitive). Treatment consists of amphotericin B, which is often given with flucytosine. Since a significant number of patients relapse after therapy, many authorities advocate chronic oral fluconazole therapy.

Roxithromycin therapy is used in treating C. pneumoniae, Legionella, and bacterial genital tract infections. This pharmaceutical, a semisynthetic derivative of erythromycin, has intracellular bioactivity, following endocytosis and concentration by phagocytes.
Correct answer:
Neisseria meningitidis

Explanation
Meningitis can be caused by bacteria, viruses, and fungi. Neisseria meningitidis is the most likely causative agent based on the Gram staining finding and the age and clinical presentation of the patient. N. meningitidis are Gram-negative diplococci usually found as normal flora of the upper respiratory tract and cause symptoms such as skin lesions, fever, malaise, and headache. N. meningitidis is the most common cause of acute bacterial meningitis in patients 18-60 years of age, and 2 classic signs of acute bacterial meningitis are positive Kernig and Brudzinski signs. Kernig sign is the inability to fully extend the knee when the hip is flexed to 90 degrees due to severe hamstring stiffness. Brudzinski sign is flexion of the hips and knees with passive flexion of the neck due to neck stiffness. Treatment for bacterial meningitis often involves vancomycin and ceftriaxone because they have good central nervous system penetration.

Bordetella pertussis is incorrect. Bordetella are Gram-negative rods causing whooping cough in humans. The organisms colonize in the upper respiratory tract and result in fever, malaise, and a cough characterized by an inspiratory gasp (whoop) producing its name. This infection is highly contagious and is spread by coughing and nasal drops. The patient in this case does not have a cough.

Francisella tularensis is incorrect. Francisella is another Gram-negative rod that is responsible for tularemia (rabbit fever). The reservoir is in rabbits, and it is transmitted by ticks. The bacteria multiply at the site of penetration in the skin and are then transported to regional lymph nodes. Patients suffer from a high fever, chills, headache, and other symptoms similar to the plague.

Haemophilus influenzae is incorrect. Although H. influenzae can cause meningitidis in infants and children 6 months to 6 years, the incidence of meningitis due to H. influenzae has declined significantly since the mid-1980's as a result of the widespread use of vaccination against this organism. The age of this patient rules out H. influenzae as the causative agent in this case.

Yersinia pestis is incorrect. Yersinia is a Gram-negative rod that causes Bubonic plague in humans. Yersinia is transmitted by fleas from rodents to humans. The patient in this case does not have Bubonic plague.
Correct answer:
a tick bite

Explanation
Lyme disease, first detected in Lyme, Connecticut, is a bacterial infection caused by the spirochete Borrelia burgdorferi. It is a zoonotic (animal-to-human) infection within the deer and rat populations and accidentally transmitted to man through the bite of the deer tick, Ixodes dammini. Different arthropod vectors are instrumental in the transmission of other Borrelia infections. The extremely small size (< 2 mm) of deer ticks makes them difficult to detect, compared to the larger wood tick, Dermancentor andersoni, or dog tick, D. varibilis. A large, circular, red petechial rash usually develops at the site of the tick bite. It may grow to over 10 cm in diameter and can become surrounded by an even more extensive halo of less intense rash. The bacteria may cause joint pain (arthlagia) resulting in a form of arthritis.

The primary lesion grows into an enlarged rash as the spirochete proliferates and invades the blood and lymphatic vessels. The lesion usually disappears after several weeks. Some individuals progress into a second stage of infection involving neurologic or cardiac abnormalities. An arthritic response may develop months to years after the initial infection, probably due to an autoimmune response. This is indicative of the third stage of Lyme disease.

Relapsing fever is another disease caused by bacteria of the genus Borrelia. It can be either epidemic (louse-borne) or endemic (tick-borne). Syphilis and leptospirosis are diseases also caused by different spirochetes.
Correct answer:
Corynebacterium diphtheriae

Explanation
Corynebacterium diphtheriae is an aerobic, club-shaped, Gram-positive rod that causes the disease diphtheria. Selective media (cystine tellurite agar) is used for the isolation and identification of the bacteria; the organism produces black colonies. The organism produces a toxin (diphtheria toxin) that is the major virulence factor; it enters the circulation and inhibits protein synthesis in a variety of tissues (the heart, nerves, and kidneys are particularly targeted). The disease will usually occur in individuals that have not been properly immunized (especially children). On physical examination, the patient will have a pseudomembrane formed at the back of the throat. This pseudomembrane is composed of bacteria, fibrin, dead epithelial cells, and red and white blood cells. Aspiration of this pseudomembrane can cause death by suffocation. In unvaccinated children, the mortality rate is approximately 20%. Treatment is usually with both antibiotics and diphtheria antitoxin.

Bordetella pertussis, a fastidious Gram-negative bacillus, is the causative agent of whooping cough. The organism is difficult to recover in cultures; therefore, PCR testing and DFA are the tests of choice because results are acquired within hours instead of days. The organism specifically binds to ciliated epithelial cells. Since the nasopharynx is lined with ciliated epithelial cells, specimens obtained from this site are more reliable at obtaining valid results then any other specimen source. The infection is limited to the upper airways and pneumonia is a rare occurrence; therefore, chest radiographs are usually normal. Children with whooping cough have paroxysms of coughing. When they gasp for breath, the sound of this inspiration is the 'whoop' of whooping cough. Abnormal oxygen exchange is common and can cause the child to turn red, and sometimes blue. Repetitive coughing can lead to vomiting or choking on respiratory secretions.

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract illness (i.e., pneumonia, bronchiolitis, and tracheobronchitis) in young children. The virus belongs to the Paramyxoviridae family and to the genus Pneumovirus. The virus is very contagious, and illnesses tend to peak in the winter or spring. Wheezing, rhonchi, rales, interstitial infiltration, and hyperinflation may be present on chest radiographs. Fevers are usually seen and range between 38° - 40° C. Hypoxemia may be profound in children. There is a need for the measurement of an infant's arterial oxygen saturation because the illness is clinically difficult to assess. Because of its contagious nature, infants in hospitals are placed in isolation to prevent outbreaks. The diagnosis of RSV can be made with reasonable accuracy based on the clinical and epidemiologic findings. Confirmation can be made by viral isolation (unfortunately this is time consuming) or by rapid diagnostic tests that are available and provide results in about 10 minutes. Ribavirin, an antiviral agent, is available for treatment of RSV in infants in whom the diagnosis is made during the early stages of the disease. It has been shown to decrease viral shedding and increase oxygenation.

Haemophilus influenzae is a small Gram-negative coccobacillus that requires 2 supplements for growth (factor X and factor V). It is non-motile, grows best at 5 - 10% carbon dioxide, and grows on chocolate agar (because of the availability of X and V factors), but not on BAP or MacConkey agar. Pneumonia due to H. influenzae Type b typically occurs in patients between 4 months and 4 years old, patients with primary lung disease, and patients that are alcoholics. Radiologic findings are those of a segmented, lobar, bronchopneumonic, or interstitial pattern (listed in descending order of frequency). Cavitation is rare. Pleural effusion occurs in about 1/2 the cases, and the fluid is usually found to be sterile when cultured.

Streptococcus pyogenes is a Gram-positive coccus, catalase-negative, and beta-hemolytic on blood agar; it appears as chains on Gram stain. Definitive identification to distinguish it from other beta-hemolytic streptococci is the detection of its specific 'A' antigen by latex agglutination techniques. Pneumonia with this organism is extremely rare; it is associated in children with streptococcal pharyngitis, scarlet fever, and streptococcal pyoderma. Bacteremia is uncommon. It is universally sensitive to penicillin.
Correct answer:
Malaria

Explanation
While many diagnoses could give symptoms similar to those described, malaria must be 1st on one's list of clinical suspicions if for no other reason than the good potential for a cure (from adequate treatment). Malaria should be considered if a febrile patient is in, or has recently left, a malarious locality. Splenectomy increases the risk of severe malaria. Malaria is an infection caused by the protozoan Plasmodium injected by anopheline mosquitoes; this causes invasion of RBCs, hemolysis, and reticuloendothelial hyperplasia. It is common in the tropics. The incubation period for P. falciparum is usually 7 - 14 days, but may be as long as 1 year if the patient is semi-immune or has taken prophylaxis. Following a prodrome of headache, malaise, myalgia, and anorexia, the patient develops paroxysms that last 8 - 12 hours; there is a sudden coldness and a severe rigor for up to 1 hour. These symptoms are then followed by high temperature, flushing, vomiting, and drenching sweats. Classical tertian and sub-tertian periodicity (paroxysms separated by 48 and 36 hours) are relatively rare. Daily (quotidian), or irregular paroxysms are more common. Signs include anemia, jaundice, and hepatosplenomegaly without lymphadenopathy or rash. There are no relapses after a successful cure. Diagnosis is by repeated microscopy of thick and thin blood films. In partially treated patients, bone marrow smears should be examined if blood smears are negative.

Schistosomiasis (bilharzias) is the most prevalent disease caused by flukes. S. mansoni is more prevalent in Africa, the Middle East, and Brazil. S. japonicum is more prevalent in South East Asia. S. haematobium is more prevalent in Africa, the Middle East, Spain, Portugal, Greece, and the Indian Ocean. The snail vectors release cercaria which can penetrate the skin (e.g., during paddling). Traveling via the lungs, the parasites finally reach the portal and then the mesenteric veins (S. mansoni and S. japonicum) or the bladder veins (S. haematobium). The eggs released from these sites cause granulomata and scarring. Clinical schistosomiasis is an immunological process on the part of the human host; it is known to be due to a type IV hypersensitivity reaction (at least to S. mansoni) to schistosomal eggs. Clinical features include abdominal pain and bowel upset, and later, hepatic fibrosis, granulomatous inflammation, and portal hypertension in the case of S. mansoni. S. japonicum affects the bowel and liver, and may migrate to the lungs and CNS. Urinary schistosomiasis (S. hematobium) starts with frequency, dysuria, hematuria, and incontinence, and may progress to hydronephrosis and renal failure. The diagnosis is based on finding eggs in the urine or feces. Treatment is with praziquantel.

Influenza is the acute infection of the respiratory tract by RNA orthomyxovirus, which has 3 types: A, B, and C. Subtyping for type A is by hemagglutinin (H) and neuraminidase (N) characteristics. The disease caused may be so mild as to pass unnoticed in some people, while in others (i.e., the elderly and the debilitated) it can cause morbidity. It may cause an epidemic or a pandemic. The symptoms include abrupt fever, malaise, headache, myalgia, vomiting, and depression. Convalescence may be slow. Serology (rising titers over 2 - 3 weeks) is helpful in establishing a firm diagnosis. Culture is possible.

American trypanosomiasis (Chagas disease) is caused by Trypanosoma cruzi and spread by reduviid bugs. The patient may present acutely with fever, lymphadenopathy, and hepatosplenomegaly; there may also be a long latent period (e.g., 20 years) followed by signs of multi-organ invasion and damage. It especially affects the heart and smooth muscle of the gut. African trypanosomiasis (sleeping sickness) is caused by Trypanosoma gambiense. It causes a slow-wasting illness with a long prepatent period (West African variety). The organism enters the skin following a bite from an infected tsetse fly; it spreads to nodes, blood, spleen, heart, and brain. Diagnosis is through demonstration of the organisms in the blood or lymph nodes. Cultures should be taken daily for 12 days. CSF should be examined.

Smallpox, a severe, highly infectious viral disease, is now eradicated. It was spread mainly by droplet infection; it caused fever, headache, muscle aches, and a severe blistering rash that left deep, pitted scars. The mortality was sometimes as high as 20%.
Correct answer:
Staphylococcus aureus

Explanation
Staphylococcus aureus is the most common Gram-positive cocci to cause clinical disease in humans. The organism is a common cause of surgical wound infections acquired in a hospital. It can also cause pneumonia, sepsis, peritonitis, sore throats, and food poisoning. S aureus is a Gram-positive cocci appearing clusters, and it is catalase and coagulase-positive.

Escherichia coli is a Gram-negative bacillus and is a member of the Enterobacteriaceae group. It is the number 1 significant clinical isolate in the microbiology laboratory. The organism is 90% lactose-positive and thus grows pink on MacConkey agar, is bile-positive on MacConkey agar, and is indole-positive and oxidase-negative. The organism is found to cause a variety of infections such as urinary tract infections, septicemia, and wound infections.

Pseudomonas aeruginosa is a lactose-negative bacillus (has no pink color on MacConkey) that is indole-negative and oxidase-positive. It is a non-fermenter and not a member of the Enterobacteriaceae group. On MacConkey, it frequently has a slight blue-green color and is said to have a grape-like odor. The organism is a common cause of nosocomial infections and is usually multiply resistant to a variety of antibiotics. It can cause eye infections, urinary tract infections, wound infections, septicemia, and ear infections.

Streptococcus pyogenes is a Gram-positive cocci that appears in pairs or chains under the microscope. The organism is beta-hemolytic on blood agar, catalase-negative, and is Lancefield grouped as A. The organism is a major cause of pharyngitis, especially in children where the infection can progress to rheumatic fever. It can cause necrotizing fasciitis in which severe damage is done to muscle tissue. The disease can progress into a toxic shock-like syndrome leading to death. Necrotizing fasciitis usually begins at an inconspicuous site of entry, such as a small vesicle. The host is prone to this infection due to some type of immunocompromised state.

Streptococcus pneumoniae is a Gram-positive cocci that is catalase-negative. On blood agar, it is alpha hemolytic and the colonies (typically) are perfectly round with an indentation in the center of the colony. The colonies are bile soluble and susceptible to optochin (P-disc). The organism is a major cause of pneumonia, meningitis, otitis media, wound infections, and septicemia.
Correct answer:
Imiquimod may be therapeutically effective.

Explanation
Imiquimod may be therapeutically effective.

Condylomata accuminata, or genital warts, are found in approximately 1% of the sexually active population in the United States and are spread by sexual contact. They are located on the genitalia internally and externally, the penis, perianal, intra-anal, and perineal areas in men and the vulva, vagina, cervix, perineal, perianal, and intra-anal areas in women. They may cause pain or itching and occasionally bleed. In moist areas, they appear as pink to red cauliflower-like growths on the mucous membrane. On dry skin, they are smaller, drier, and have a yellowish-gray color.

Originally thought to be caused by venereal diseases, such as syphilis, a spirochete, or gonorrhea (gram-negative intracellular diplococci), the recognition that genital warts are a distinct disease entity was recognized in 1917. Extracts of condylomata from the penis of a medical student who had no other symptoms were inoculated on the forearms of the researcher and his assistant, and on the genitalia of a virgo intacta. After 2.5 months, the men developed flat warts on their arms, and the woman developed genital warts. Approximately 97% are caused by human papillomavirus (HPV) types 6 or 11 (low-risk mucosal HPVs). These viruses replicate as episomes and rarely incorporate their DNA into the host DNA. However, 60 different types of HPV have been associated with Condylomata accuminata. These are almost always benign lesions, and they do not lead to malignancy. Risk factors for acquiring the infection are:

Smoking
Oral contraceptives
Multiple sexual partners
Early coital age
Dietary factors
Immunosuppressive conditions, including HIV infection
Polymorphisms in the human leukocyte antigen system
Other sexually transmitted infections such as chlamydia or herpes simplex virus
Failure of men to use condoms during sexual intercourse
Condoms are not particularly effective in preventing the spread of condylomata, as the uncovered skin in pubic region is susceptible. Studies have demonstrated circumcision to be protective against the acquisition of the disease. Viral shedding may occur when no visible warts are present and may be transmitted through semen to a sexual partner.

High-risk HPVs cause squamous intraepithelial lesions. HPV has been identified in 99.7% of all cervical cancer. Infection with high-risk HPV types such as 16, 18, 31, 33, and 45 is necessary for the development of cervical cancer. Persistent HPV infection is necessary for the development of high-grade squamous intraepithelial lesions (HSIL). Throughout the world, HPV 16 accounts for 40-60% of invasive cervical cancers.

Treatment is only needed based on the patient's personal preference. Imiquimod, an immune modifier, induces secretion of cytokines, including alpha-interferon. Interferons are intracellular signaling proteins (cytokines) produced by cells in response to various stimuli. Alpha-interferons are synthesized and secreted by leukocytes and lymphoblasts. They have antiviral properties, and clinical trials have shown Interferon-alfa 2b to be an effective first-line drug in treating Condylomata accuminata. They also have anticancer properties and have been found to be effective against hairy cell leukemia. As immunomodulators, they are used in the treatment of hepatitis B and hepatitis C. Imiquimod is not recommended for treatment of rectal, cervical, intravaginal, urethral, and intra-anal human papilloma infection. When used, it is applied as a topical cream. Interferon-alfa 2b has been used as an intralesional injection. Other treatments include topical podophyllin, an antimitotic agent whose mechanism of action is unknown, topical 5-fluorouracil, an antineoplastic agent that interferes with DNA synthesis, and trichloroacetic acid, a topical drying agent.

For unresponsive cases, cryotherapy, curettage, electrodesiccation, surgical excision, carbon dioxide laser treatment, or combination therapy may be indicated. No treatment is curative, however, and there is a high likelihood of recurrence.
Correct answer:
Blood culture positive for S. typhi

Explanation
Definitive diagnosis depends on a positive blood culture for Salmonella typhi. The term 'enteric fever' includes typhoid caused by the Salmonella enterica serotype, typhi (referred to as S. typhi), and paratyphoid caused by Salmonella paratyphi A, B, and C. Isolation of S. typhi from stool and urine samples helps in the diagnosis, but could also be positive in carriers. Due to various factors, the interpretation of agglutinin titers detected in a single serum sample is difficult.

In enteric fever, the infection is acquired by ingestion. After reaching the small intestine the bacteria invade the mucosa, reaching the mesenteric lymphoid follicles and the draining mesenteric lymph nodes. Some pass to the reticuloendothelial cells of the spleen and liver where Salmonellae are able to survive and multiply within the mononuclear phagocytic cells. Depending on the virulence of the bacteria and host response, bacteria are released into the blood stream and become widely disseminated. The bacilli are seeded in the liver, spleen, gall bladder, bone marrow, and Peyer's patches of the terminal ileum, where further multiplication occurs. The lungs and kidneys may be involved. Toward the end of the incubation period (7-14 days) massive bacteremia occurs, leading to the onset of clinical symptoms. During the first week of clinical disease, Salmonella can be isolated from blood culture in 60-80% of patients. As the humoral and cellular responses of the host come into action, the chances for isolation from the blood gradually decrease. Since multiplication of organisms occurs in the intestinal lymphatic tissue and in the gall bladder, Salmonellae are excreted in feces. The stool culture positivity rate is greater during the second and third weeks of illness.

When Salmonellae localize in the kidneys, they are excreted in urine (infrequently and in small numbers). It is possible to isolate the organisms from urinary deposits by inoculating enrichment media. The sensitivity of the blood culture is reduced by prior administration of antibiotics. In such patients, bone marrow culture is very useful for the isolation of the bacteria. Positive results are obtained in 80-95% of patients with typhoid and are not affected by the duration of the illness and/or prior antibiotic therapy. DNA probes and PCR-based tests have been developed to detect S. typhi directly in blood, though these are not available for use in many areas where typhoid is common. Prevalence of multidrug-resistant (MDR) S. typhi (e.g., resistant to chloramphenicol, ampicillin, and trimethoprim/sulfamethoxazole) is a major problem faced by countries where typhoid is endemic. The resistance is plasmid-mediated. Third-generation cephalosporins and fluoroquinolones are recommended for treatment of infections by MDR strains. Recently, the emergence of strains with reduced susceptibility to fluoroquinolones has been noticed. This is chromosomally-acquired resistance and is largely due to mutations in the gyrA gene. Development of resistance to ceftriaxone has been reported, though is rare in occurrence. In making appropriate decisions regarding the choice of an antibiotic for the treatment of typhoid, susceptibility testing of the isolate is very important.

A positive stool culture is helpful in diagnosis, though it is not always confirmatory. Fecal carrier state is common after clinical, as well as subclinical, infection by Salmonella typhi. In fecal carriers, Salmonellae persist in the gall bladder and the biliary tree, and they are excreted in the feces (intermittently). The chronic carrier state is seen more commonly in patients with cholelithiasis. Demonstration of Vi agglutinins in the serum and culture of stool and bile samples are useful for detection of carriers.

Urine culture can be positive in urinary carriers; urinary carriers are less frequent than fecal carriers. The carrier state is generally associated with some abnormality of the urinary tract (e.g., calculi or schistosomiasis).

O (somatic) and H (flagellar) agglutinins against Salmonella typhi and paratyphi are tested by Widal agglutination assessment. A single serum sample test result has no diagnostic significance. Serum agglutinins usually appear by the end of the first week and rise sharply during the second and third weeks of Salmonella infection. A rise in the titer of agglutinins is indicative of active infection, and it is demonstrated by testing at least 2 samples of serum that are taken at an interval of 7-10 days. Demonstration of a 4-fold rise in the titer of agglutinins against H and O antigens of S. typhi can be helpful in diagnosing typhoid during later stages of the disease when a blood culture is often negative. Though a high titer of O agglutinins could be suggestive of recent infection, the possible presence of cross-reacting antibodies limits the utility of this test.

H agglutinins are influenced by a previous infection and past immunization against typhoid. They persist for a longer period than O agglutinins. Though the Widal test is still used for the diagnosis of enteric fever in countries where the disease is endemic, the test faces controversies. Widal test results are influenced by a variety of factors (e.g., previous antibiotic therapy, previous immunization with Salmonella antigens, and cross-reacting antibodies to other infectious agents); therefore, the interpretation of the test should be done with caution. Information on the distribution of agglutinin levels in normal sera and in different geographical areas may help to assess the significance of the test results. During recent years, rapid tests such as Dot blot and DOT enzyme immunoassay for serodiagnosis of enteric fever have been developed and evaluated. The results are promising, and these tests are reported to be of use in regions where typhoid is endemic and laboratory facilities are limited.
Correct answer:
Borrelia burgdorferi

Explanation
Borrelia burgdorferi is a spirochete, and it is the etiologic agent of Lyme disease. The organism is transmitted to the host by the bite of a tick (Ixodes scapularis). The spirochete produces symptoms in the host such as headache, fever, arthritis-like pain in the joints, and a variety of neurological symptoms. Typically, at the site of the tick bite and introduction of the spirochete, a characteristic rash develops; it is target-like in appearance with expanding borders. Only the nymph and adult stage can transmit the spirochete. Co-infection with Babesia microti and/or Ehrlichia chaffeensis is common.

Francisella tularensis is coccoid to ellipsoid in shape and very small. It is Gram-negative and non-motile, appearing singly. The organism is a strict aerobe. The organism is the causative agent of tularemia (rabbit fever, deerfly fever, market men's fever). The onset of the disease is sudden and includes flu-like symptoms, as well as characteristic ulcer with regional lymphadenopathy. The source of infection is the exposure to infected wild and domestic animals or their products, contaminated water, ingestion or inhalation, and blood-sucking arthropods. The organism is highly infectious, and it is the third most commonly reported laboratory associated infection. Direct isolation is best done by culturing the ulcer, pharynx, conjunctiva, lymph node biopsy, and gastric washing.

Rickettsia rickettsii is a rickettsial organism that is transmitted by the bite of a tick that causes Rocky Mountain Spotted Fever. The most common tick to carry Rickettsia rickettsii is Dermacentor variabilis (common dog tick). Common initial symptoms present 2-14 days after the tick bite. These symptoms include a macular rash that initially starts on the palms and lower extremities (eventually spreading to cover the entire body), purpura, emesis, myalgias, fever, diarrhea, hypotension, and DIC. If the disease is not treated properly without delay, it is not uncommon for the patient to develop DIC and shock, with death as the eventual outcome. When Rickettsia rickettsii infection is suspected, the antibiotics of choice are Tetracycline or chloramphenicol.

Ehrlichia chaffeensis, an obligate intracellular Gram-negative species of rickettsiales bacteria, causes ehrlichiosis (also known as "Rocky Mountain spotted fever"). The organism infects mononuclear cells, mainly monocytes and macrophages. Patients generally present with a febrile illness and complaints of headache, myalgias, malaise, and fever. Patients also present with elevated liver enzymes and a leukopenia that can cause anemia. The organism will produce characteristic cytoplasmic inclusions; they can be seen by microscopic examination of peripheral blood or bone marrow smears.

Babesia microti is the etiological agent that causes babesiosis. Initial symptoms of babesiosis usually begin gradually and mimic those of influenza. There is malaise, aches and joint pain, headache, shaking chills with fever, abdominal pain, nausea, vomiting, fatigue, and anorexia. There is also dark urine, photophobia, and psychological symptoms. Adult respiratory distress syndrome is not uncommon. The destruction of RBCs produces anemia, thrombocytopenia, proteinuria, and hemoglobinuria. BUN, serum creatinine, and bilirubin can be elevated. Liver enzymes can also be elevated. Diagnosis can be made by the observation of characteristic ring forms in the red blood cells of a Giemsa-stained peripheral smear. The clinical history and lack of gametocyte forms on the peripheral smear help eliminate plasmodium as an identification. Most cases of babesiosis have occurred in the northeastern coastal region of the United States, particularly Cape Cod, Block Island, Nantucket, Martha's Vineyard, Eastern Long Island, Shelter Island and Fire Island, and the Connecticut mainland. Cases have also occurred in Washington State. Deer are a necessary host, and the White Footed Mouse acts as a reservoir. The Deer Tick nymph (Ixodes scapularis) is the primary vector.
Correct answer:
Shigella sonnei

Explanation
The most likely cause of seizures in a patient with dysentery is shigellosis. This infection, caused by Shigella sp., is characterized by abdominal pain, fever, emesis, urgency, painful defecation, and diarrhea. The diarrhea may be watery and voluminous, and it may progress to frequent bloody stools. Neurologic findings such as convulsions, headache, lethargy, and nuchal rigidity are found in up to 40% of hospitalized infected children. Other major complications include dehydration, bacteremia, sepsis, and DIC. These occur more often in young, malnourished patients.

Campylobacter organisms are important causes of bacterial gastroenteritis and systemic infections, especially in newborns and immunocompromised patients. These thin, Gram-negative rods cause acute gastroenteritis, bacteremia, and focal extraintestinal infections such as meningitis, pancreatitis, cholecystitis, urinary tract infections, peritonitis, and arthritis. Seizures are rare with this infection.

Non-typhoidal Salmonella infections, caused by a motile, nonencapsulated, Gram-negative rod, may cause a dysenteric picture; however, they do not typically cause seizures. Acute gastroenteritis and bacteremia are common infections. Osteomyelitis is seen in patients with sickle-cell anemia. Suppurative arthritis may occur at sites of previous skeletal trauma. Meningitis is primarily found in neonates.

Giardia lamblia is a protozoon that causes diarrhea and abdominal pain with cramps, but it is not associated with seizures.

Rotavirus is the most important cause of dehydrating diarrhea in early childhood, but it usually produces a watery diarrhea and does not cause seizures, except in the case of severe electrolyte imbalance.
Correct answer:
Group A Streptococcus infection of the upper respiratory tract

Explanation
The correct answer is group A Streptococcus infection of the upper respiratory tract, as this type of infection is a prerequisite to the development of ARF. Patients typically experience pharyngitis about 2-4 weeks earlier than the onset of symptoms associated with ARF.

In addition to the preceding infection, there are other criteria, called Jones criteria, required to diagnose a patient with ARF. The major Jones criteria include carditis, erythema marginatum, subcutaneous nodules, chorea, and arthritis. The minor Jones criteria include fever, polyarthralgias, reversible prolongation of the PR interval on EKG, history of rheumatic fever, rapid erythrocyte sedimentation rate, and a history of streptococcal infection. Either 2 of the major criteria or 1 major and 2 minor criteria are required for the diagnosis of ARF.

Proteus mirabilis infection of the urinary tract is not the correct answer. This organism can be seen in the urine, particularly in patients with renal calculi, and can lead to irritative voiding complaints. However, this type of infection would not predispose a patient to ARF.

Helicobacter pylori infection of the GI tract causes inflammation of the lining of the GI tract. It has been linked to the development of ulcers, gastritis, and even stomach cancer.

Haemophilus influenza infection of the upper respiratory tract is not the correct answer, as this organism does not lead to ARF. H. influenza can be responsible for various diseases, including pneumonia, bacteremia, bacterial meningitis, and otitis media.

E. coli infection of the urinary tract is not the correct answer, as this organism does not lead to ARF. E. coli is the most common cause of uncomplicated urinary tract infections.
Correct answer:
Cryptococcus neoformans

Explanation
Cryptococcus neoformans is an opportunistic yeast. It is the most common agent causing central nervous system infection in patients with HIV. Cryptococcus neoformans meningitis usually begins as an asymptomatic pulmonary infection that progresses to fungemia and meningitis in the immunocompromised individual. The organism's natural habitat is the soil, and it is found to grow well in pigeon droppings. Areas with an abundance of pigeons are particularly good sources of infection for these individuals. The India ink prep is a quick test that can be used to detect the presence of Cryptococcus neoformans in the CSF. The organism has a large capsule surrounding it that is impenetrable to the India ink; a clearing is seen around the organism when examined microscopically. However, the test has limited sensitivity. Antigen detection tests are more sensitive, but the turn-around time is considerably longer.

Neisseria meningitidis is a Gram-negative diplococci that is kidney bean-shaped. It is a major cause of meningitis in young children and young adults. It is gamma hemolytic on blood agar. Infants have protective immunity from the mother that wanes as they approach childhood.

Streptococcus pneumoniae is a Gram-positive lancet-shaped coccus that is catalase-negative and occurs in pairs. It is a common cause of meningitis, but is more common in elderly people and especially those that have underlying conditions, are malnourished, or are alcoholics. The organism is alpha-hemolytic on blood agar.
Correct answer:
Herpes zoster

Explanation
Reactivation of the varicella-zoster virus results in Herpes zoster (shingles). Symptoms of herpes zoster include the warning symptoms of unilateral eruption, which include a tingling or burning sensation that is limited to a specific part of the body. The common sites of cutaneous involvement include the thorax, followed by the neck, face, and lumbosacral area. The prodromal phase is followed by the appearance of characteristic skin lesions, beginning as a maculopapular rash that follows a dermatomal distribution. The maculopapular rash evolves into vesicles on an erythematous base. Vesicles appear as dense, deep, small blisters (vesicles) that ooze and crust. The cutaneous lesions heal in 7-10 days; they result in scarring and pigmentary changes. Lymph node swelling may occur. Herpes zoster is accompanied by excruciating pain and an intense burning sensation. Ocular complications (mucopurulent conjunctivitis, episcleritis, keratitis, and anterior uveitis) occur when there is involvement of the ophthalmic division of the trigeminal nerve.

The three main objectives in the treatment of Herpes zoster are treatment of the acute viral infection, management of the acute pain associated with herpes zoster, and the prevention of postherpetic neuralgia. These objectives are fulfilled by the use of antiviral agents, oral corticosteroids, and adjunctive individualized pain management modalities.

The symptoms of Herpes simplex virus 1 (HSV-1) can be very painful. Blisters typically form on the lips, but they may also erupt on the tongue. The blisters eventually rupture as painful open sores. Healing occurs without scarring, and blisters disappear in 3-14 days. Increased salivation and foul breath may be present. The infection may be accompanied by difficulty in swallowing, chills, muscle pain, or hearing loss. About 60% of HSV-1 infections recur within a year. Recurrences are usually much milder than primary infections, and they are known commonly as cold sores or fever blisters.

The infection with Herpes simplex virus 2 (HSV-2) usually occurs in or around the genital area 2-8 days after exposure to the virus. Flu-like discomfort and fever, nerve pain, itching, lower abdominal pain, urinary difficulties, and yeast infections (in women) may precede or accompany the eruption of the characteristic skin blisters. A new crop often occurs during the second week, and it is accompanied by swollen lymph glands in the groin. The symptoms may last as long as 6 weeks. In many cases, women whose lesions occur inside the vagina may be unaware that they have HSV-2. Lesions inside the vagina can cause a discharge, but they are not visible and cause minimal nerve pain. The outbreak of infection is often preceded by an early group of symptoms, known as a prodrome, which may include itchy skin, pain, or an abnormal tingling sensation.

Impetigo is a skin disorder characterized by crusting skin lesions that is caused by bacterial infection. It may follow a recent upper respiratory infection, such as a cold or other viral infection. It is similar to cellulitis, but more superficial, involving the superficial skin. It is caused by streptococcus, staphylococcus, or both. Typically, this lesion begins as a cluster of tiny blisters that burst, followed by oozing and the formation of a thick honey-colored or brown-colored crust that is firmly stuck to the skin. Local lymph nodes near the infection may be swollen.

The usual cause of folliculitis is bacteria (usually Staphylococcus). It can also be caused by a fungus. It may occur anywhere on the skin, and it is usually the result of injury or damage to a hair follicle. The injury can be caused by friction from clothing, blockage of the follicle, or by shaving. Symptoms include a rash, pimples, or pustules located around a hair follicle that may crust over, itching, and erythema of the skin.
Correct answer:
Doxycycline

Explanation
The patient case scenario results in a diagnosis of Rocky Mountain Spotted Fever (RMSF). This is a spirochetal disease that is spread via an infected tick. Despite its namesake, diagnosis of this has been highest in the following states: Arkansas,Delaware, Missouri, North Carolina, Oklahoma, and Tennessee, which is of course where our patient had traveled the week prior to her visit. Incidence of RMSF is highest during the summer months, specifically June and July.

Symptoms of RMSF typically begin around 2-14 days after the bite of the tick; many times patients will not even realize or feel the bite. Various symptoms that a patient may present with include the following: fever, rash, headache, nausea, vomiting, abdominal pain, muscle pain, lack of appetite, or even conjunctival injection. Patients will typically not experience the full extent of the list and may only have a few of the symptoms.

The classic rash of RMSF is a rash that first appears usually around 2-5 days after onset of a fever and will be small, flat, pink non-pruritic macules that appear on the wrists, forearms, and ankles and spread to include the trunk and potentially the palms and soles. A more red to purple, petechial rash is typically present after the 6th day of symptoms.

Treatment should be initiated as soon as diagnosis is made. Doxycycline is the first line treatment for adults and children of all ages and should be initiated immediately whenever RMSF is suspected. Another option that may be considered is chloramphenicol.
Correct answer:
Observe the child and reassure the parent.

Explanation
The clinical syndrome in this vignette is typical for roseola infantum, also known as exanthem subitum. Typically, the patient will have a moderate-to-high fever for 3-4 days, followed by defervescence and the outbreak of an erythematous macular or maculopapular rash that usually begins on the trunk, spreads to the arms and neck, and occasionally affects the face and legs. The rash is usually gone within 3 days. Occasional cervical lymphadenopathy is seen, as well as a slight pharyngeal inflammation and coryza. The patient can present with a bulging fontanelle and suffer from febrile convulsions during the high fever stage of the illness.

Human Herpesvirus 6 is the etiologic agent of the vast majority of cases. Once the rash has appeared and the child appears well, the only treatment is reassurance for the parents in regard to the benign nature of the condition.

Patients with the pre-rash presentation can cause a diagnostic challenge in that pneumococcal bacteremia may also present with a high fever and a well-appearing child. In that case, a CBC and blood culture may guide therapy towards perhaps presumptive treatment with antibiotics until the blood culture results were known.

Oral acyclovir might be used for the treatment of varicella (chickenpox). These lesions appear as intensely pruritic erythematous macules and evolve to clear fluid-filled vesicles. Clouding and umbilication of the vesicles occur between 24 and 48 hours, and it is followed by the crusting over of the lesions and development of scabs. Different lesions will be found in different stages of development at the same time during the illness. The average number of lesions is approximately 300.

Measles titers are appropriate in the setting of a typical measles exanthem and prodrome. The prodrome typically presents with the triad of cough, conjunctivitis, and coryza. Koplik spots may be seen in the buccal mucosa opposite the lower molars at this time. The rash appears as faint macules on the upper neck, behind the ears, and along the hairline. The rash quickly spreads to the face, upper arms, entire neck, upper chest and onto the back, abdomen, entire legs, abdomen, and finally to the feet. The temperature rise usually occurs with the onset of the rash, and it dissipates when the rash reaches the feet.
Correct answer:
Acute rheumatic fever

Explanation
The patient in the above scenario most likely has acute rheumatic fever. Rheumatic fever is a systemic immune process that is often a complication of undertreated b-hemolytic streptococcal infection of the throat, resulting in inflammatory changes in the heart, skin, joints, and other tissues.

Clinical presentation of acute rheumatic fever is often an acute febrile illness and a migratory polyarthritis of the larger limb joints. Cardiac symptomatology is less common but can manifest as murmurs or a friction rub, indicating valvular and pericardial involvement respectively.

The diagnosis of acute rheumatic fever is based on clinical features plus evidence of a preceding streptococcal infection. The Jones criteria for diagnosis of acute rheumatic fever were developed in 1944 and most recently updated in 1992. The presence of two major criteria, or one major and two minor criteria, establishes the diagnosis. Major criteria include:
Carditis - including evidence of pericarditis, cardiomegaly, congestive heart failure, or mitral/aortic valvular disease;
Erythema marginatum - a rash consistent of rapidly enlarging macules that assume a ring-like or crescent shape;
Subcutaneous nodules - palpable small, firm, nontender nodules that present primarily over bony prominences;
Sydenham chorea - involuntary choreiform movements of the face, tongue and upper extremities; and
Migratory polyarthritis involving the large joints.
Minor criteria include fever, arthralgias/myalgias, previous diagnosis of rheumatic fever or rheumatic heart disease, evidence of systemic inflammation (elevated ESR or C-reactive protein), plus supporting confirmation of recent streptococcal infection (positive throat culture or elevated anti-streptococcal antibody titers).

Pericarditis is an inflammation of the pericardial sac surrounding the heart; it has many possible etiologies. Common presentations include acute onset of pleuritic chest pain and a friction rub.

Pleurisy is an inflammation of the parietal and/or visceral pleura that lines the chest wall and the lungs. It can present as chest pain that worsens with inspiration or deep breathing (pleuritic chest pain).

Endocarditis is an infection of the valvular or endocardial surface of the heart, primarily caused by bacterial or fungal pathogens. The clinical presentation varies greatly depending on the infecting organisms and the areas of the heart that are affected. Symptoms can include non-specific low-grade febrile illness; chest pain, cough, dyspnea, and arthralgias. Physical examination can reveal petechiae of the palate, conjunctivae, or peripheral extremities; painful violaceous lesions of the fingers, toes, or feet (Osler's nodes); Janeway lesions (erythematous lesions of palms and soles), subungual "splinter" hemorrhages, and Roth spots (retinal exudates). Patients can also present with signs/symptoms of embolic events.

Influenza is a highly contagious viral infection that is primarily transmitted via respiratory droplets. Symptoms include a sudden onset of fever, chills, malaise, myalgias, headache, substernal soreness, cough, sore throat, and nasal congestion.

While pericarditis, pleurisy, endocarditis, and influenza can all be included in the differential diagnosis of this patient, the complete clinical presentation, as well as the positive anti-streptococcal antibodies make acute rheumatic fever the most likely diagnosis.
Correct answer:
Giardiasis

Explanation
Diarrhea can be a manifestation of all of the diseases listed. Among these diseases, giardiasis is the only infection that is diagnosed by microscopic detection of motile trophozoites of the etiological agent in stool. Other manifestations described are also commonly observed in giardiasis.

Giardiasis is a parasitic infection caused by an intestinal flagellate, Giardia lamblia (Giardia intestinalis). G.lamblia is the most common intestinal protozoan pathogen of humans. Giardiasis, an infection occurring worldwide, is common in day care centers and institutionalized individuals; it often occurs as outbreaks. It is transmitted by ingestion of food and water contaminated with cysts of the organism. Although in some individuals the disease may be asymptomatic, most people present with acute watery diarrhea associated with abdominal discomfort, bloating, and foul-smelling feces. Giardia cysts can be detected in stool samples of persons with symptomatic and asymptomatic infections. Immunosuppressed persons are susceptible to massive infection and severe clinical manifestations. The most widely used drug for treatment of giardiasis is metronidazole. Tinidazole and nitazoxanide are other drugs of choice.

Cryptosporidiosis is a highly infectious disease caused by Cryptosporidium hominis. Outbreaks of diarrhea due to cryptosporidiosis are commonly found in day care centers, transmitted by ingestion of food or water contaminated with oocysts of the parasite. Cryptosporidium has assumed great importance as a frequent cause of severe intractable diarrhea in AIDS patients. Diagnosis is established by demonstration of sporulated oocysts in the feces by modified acid-fast or other staining methods, such as fluorescent staining with auramine phenol. Nitazoxanide and paromomycin are drugs effective against cryptosporidiosis.

Cyclosporiasis is an infection caused by Cyclospora cayetanensis. Infected patients manifest with diarrhea, usually between 2 and 11 days after consumption of food or water contaminated with oocyst-laden feces. The diagnosis is established by identification of oocysts in stool samples stained by modified safranin, acid-fast, or by autofluorescence with UV-light microscopy. Treatment is with trimethoprim-sulfamethoxazole

Isosporiasis, caused by Isospora belli, is commonly found in outbreaks in day care centers and mental institutions. After an incubation period of 7 to 11 days, patients manifest with watery diarrhea that can persist for several months. Diagnosis rests upon detection of oocysts in freshly passed stools. Stool concentration techniques are usually necessary, as the presence of the parasite in the feces is scant. Treatment is with trimethoprim sulfamethoxazole.

Microsporidiosis is caused by microsporidia, minute intracellular parasites that reproduce by spores. Microsporidia had been known as animal parasites, but are now increasingly recognized as a group of parasites causing opportunistic infections in humans, mostly in AIDS patients. They can cause a wide range of illness from diarrhea to involvement of the CNS, eyes, viscera, muscles, and disseminated disease. Diagnosis is established by visualization of spores of microsporidia in stools, body fluids, or tissues after appropriate staining or electron microscopy. Albendazole is effective against microsporidiosis.
Correct answer:
Perform arthrocentesis of the right ankle with analysis of the synovial fluid.

Explanation
In this patient, the acute onset of symptoms, low-grade fever, and lack of trauma warrant a prompt evaluation. Empirical therapy will not provide a definitive diagnosis and could potentially result in a serious illness, such as septic arthritis, being missed. The most appropriate initial evaluation of a patient with monoarticular arthritis is arthrocentesis. Joint aspiration should be performed with aseptic technique as a part of the evaluation of every case of acute monoarthritis. Analysis of the synovial fluid includes a WBC count, differential, appropriate cultures and stains for microorganisms, and polarized-light microscopy. The WBC count in the synovial fluid is useful in distinguishing inflammatory from noninflammatory arthritis; levels greater than 2,000/mm3 are consistent with inflammation. Gonococcus (Neisseria gonorrhea) is the most common cause of infective arthritis in young adults.

In this particular case, the ankle of the patient is swollen due to gonococcal arthritis. Gonorrhea is the most frequently reported communicable disease in the U.S. Disseminated gonococcal infection is most often the cause of acute septic arthritis in sexually active adults and the reason for most hospitalizations due to infective arthritis.

Patients with crystal-induced arthritis usually have counts in excess of 30,000/mm3. The finding of monosodium urate or calcium pyrophosphate dihydrate crystals on polarized light microscopy is pathognomonic for gout and pseudogout, respectively. Negatively birefringent crystals under a polarizing microscope means gouty arthritis and positively birefringent crystals under a polarizing microscope is pseudogout. Important to note is that the absence of crystals does not exclude these diagnoses. The serum level of uric acid is of little use in diagnosing gouty arthritis. 20% of patients with gout have normal uric acid levels, and most persons with elevated levels never develop gouty arthritis. Plain radiography is most useful in patients with significant trauma that suggests the possibility of fracture, in those who experience a sudden loss of function, and in those with symptoms that do not improve despite appropriate treatment. This patient did not have any recent trauma and was still able to bear weight (although it did cause pain).

Chondrocalcinosis would suggest the diagnosis of pseudogout, but arthrocentesis is the initial step.
Correct answer:
Tdap vaccine plus antibiotics

Explanation
The correct response is a Tdap vaccine plus antibiotics. This patient has not received a tetanus booster for over 10 years. According to the immunization schedule, those patients who have received a primary course of 3 doses of DTaP (diphtheria, tetanus inactivated toxoids, and acellular pertussis) given from 2 months to 5 years should receive booster doses 10 and 20 years after the primary course. If more than 5 years have elapsed since the last dose, a booster dose of Tdap (tetanus, diphtheria toxoid, acellular pertussis) is indicated. This vaccine is recommended for children over 7 years old and adults; the lower case "d" and "ap" indicate that the vaccine contains smaller doses that the primary vaccine course. Tdap is preferred to Td (tetanus and diphtheria toxoid only) because of the resurgence of pertussis infections due to waning immunity. In children younger than 7 years, DTaP or DT, if pertussis vaccine is contraindication or allergy is present, is the appropriate therapy.

In the case of a dirty wound, antibiotics are usually administered in addition to vaccination to prevent the risk of infection.

Tetanus immunoglobulin is given if the individual has not received at least 2 previous tetanus toxoid shots, or if the tetanus-prone wound has not been treated for more than 24 hours.

Tetanus toxoid only is adequate to prevent the development of tetanus from the dirty wound but does not address the fact that the patient also requires a diphtheria and acellular pertussis booster. In addition, in the context of an acute wound, antibiotics are usually administered as a precaution along with tetanus toxoid.

Prescribing only antibiotics is not appropriate, as it fails to address the patient's need for boosters to prevent tetanus and diphtheria.

Of note, some patients have contraindications to Td, such as a history of allergy or adverse vaccine reaction, unstable neurological condition, or acute illness. In these patients, passive immunization with tetanus immunoglobulin may be indicated.
Correct answer:
Acute rheumatic fever

Explanation
Acute rheumatic fever is the correct response; the scenario identifies 2 major Jones criteria: migratory polyarthritis and carditis. Arthritis with acute rheumatic fever typically starts in the legs and then migrates; most commonly, it affects the large joints. The pain can subside within 1 - 2 days, and the arthritis starts affecting another joint. Swelling and redness are common over the joints involved. Typically, a mitral or aortic regurgitation murmur is noted on exam. A friction rub indicates involvement of the myocardium. Polyarthritis and carditis are the most common major Jones criteria for acute rheumatic fever. A confirmed group A Streptococcus test needs to be done, but with the sick contact, you can safely assume the patient has strep.

Juvenile idiopathic arthritis is incorrect; it would not explain the tachycardia or other abnormal cardiac physical exam findings. The eyes can be involved with juvenile idiopathic arthritis, which was not the case with the above patient.

Systemic lupus erythematosus is incorrect; based on his history, the patient does not have the 4 required criteria from the American College of Rheumatology necessary to make the diagnosis. No rash was noted on exam. Nothing was stated about pleuritis, anemia symptoms, seizures, or positive ANA.

Kawasaki disease is incorrect because there was nothing stated about a long-lasting high fever, conjunctivitis, rash, 'strawberry' tongue, redness on palms and soles, and/or swollen lymph nodes. Joint pain can present during the 2nd phase of Kawasaki's disease, but based on the overall scenario, Kawasaki's disease is an unlikely answer.

Septic arthritis is incorrect because typically only one joint is involved and this would not explain the cardiac symptoms. Children can usually bear weight on the extremity involved.
Correct answer:
Metronidazole

Explanation
This Hispanic patient has amebic liver abscess. Treatment is with metronidazole for 7-10 days. Because metronidazole is well-absorbed from the intestines, oral administration is adequate. If diagnosed early and treated promptly, amebic liver abscess has a very low mortality. In contrast, pyogenic liver abscess is associated with high spiking fevers, signs and symptoms of sepsis, jaundice, and a focus of infection in the peritoneal cavity or biliary tract. Ultrasound may show multiple abscesses rather than a single abscess due the mode of hematogenic transmission.

The risk factors are his origin, recent travel to Mexico (which is endemic for amebiasis), and typical signs and symptoms. Preceding diarrhea may be seen. Amebiasis is caused by the protozoan Entamoeba histolytica. The parasite exists in 2 forms: a cyst stage, which is the infective form, and a trophozoite stage, which is the form that causes invasive disease. Most infections occur in developing countries due to poor socioeconomic conditions and sanitation levels. In developed countries, such as the United States, amebiasis is mainly seen in migrants from and travelers to endemic countries. Most infections are asymptomatic, but amebic dysentery, amebic liver abscess, and rarely other manifestations such as pulmonary, cardiac, or brain involvement can occur. Fever, abdominal pain, pleuritic chest pain, mild elevation of liver enzymes, and leukocytosis without eosinophilia are characteristic. Stool culture may be positive for E. histolytica in 75% of cases.
Correct answer:
Itraconazole

Explanation
The correct response is itraconazole.

Histoplasmosis is a chronic respiratory infection caused by inhaling the spores of the fungus Histoplasma capsulatum, found in bird and bat droppings common along river valleys. Most cases are mild or asymptomatic. Risk factors include travel or residence in central/eastern United States or South America, environmental or occupational exposure to droppings of chickens, bats, or blackbirds, pre-existing COPD (chronic obstructive pulmonary disease), and immunocompromised people. Symptoms include fever, chills, cough (with mucus or pus), skin lesions, and joint stiffness. The associated skin lesion usually presents as a lesion on the mouth or inner cheek as a papule; it may ulcerate. Tests include chest X-ray, sputum culture, (invasive) open lung biopsy, bronchoscopy (with or without transtracheal biopsy), histoplasma complement fixation titer, and CBC. 2015 updated guidelines recommend Itraconazole 200 mg 3 times daily for 3 days and then 200 mg once or twice daily for 6-12 weeks for patients who continue to have symptoms for 11 months (B-III).

Acute pulmonary eosinophilia is a self-limiting inflammation of the lungs associated with infiltration of eosinophils in the lungs and blood. The etiology includes exposure to various drugs, parasitic infestation (especially ascariasis in children), nickel exposure, recent blood transfusion, or lymphangiogram. Symptoms may include malaise, loss of appetite, fever (greater than 2 to 3 days), productive cough (mucoid sputum), chest pain, shortness of breath, wheezing, rapid respiratory rate, headache, and muscle pain. Tests include auscultation of the lungs (revealing fluid), bronchoscopy (showing hypersensitivity reaction), open lung biopsy (invasive way to show hypersensitivity reaction), CBC (increased white blood cell count, particularly eosinophils), sputum smear (KOH test), and chest X-ray. If a cause is found, therapy consists of removing the offending drug or treating the infection with antibiotic therapy. If no cause is found, steroid therapy should be given.

Pulmonary actinomycosis is an infection caused by Actinomyces israelii or actinomycete bacteria; the infection causes disease of the chest, mouth, jaw, and pelvis. The bacterium is in the normal flora of the mouth and gastrointestinal tract of humans. Symptoms include lethargy, weight loss, fever, productive cough, draining sinuses, night sweats, shortness of breath, and chest pain. Poor dental hygiene and a dental abscess may predispose it to facial lesions. In the chest, it results in cavities in the lung and pleural effusion, which may spread through the chest wall and produce sinuses. Tests include a CBC (showing anemia), chest X-ray, culture of specific tissue, and bronchoscopy with culture. The goal of treatment is to control infection. Long-term treatment with penicillin or an alternative is necessary to ensure a cure. Surgical drainage of the pleural effusion and surgical resection of lung lesions may be necessary to control the infection.

Acute coccidioidomycosis is a disease caused by breathing in a fungus found in the soil in certain parts of the southwestern United States, Mexico, and Central and South America. Dark-skinned people and people with a weak immune system will have more serious infections. Infection is caused by breathing in the spores of a fungus (Coccidioides immitis) found in desert regions. About 60% of infections cause no symptoms and are only recognized by a positive coccidioidin skin test. Symptoms include cough, chest pain (mild pain to severe constriction), fever, chills, night sweats, headache, muscle aches and stiffness, joint stiffness, and rash on the lower legs (erythema nodosum). Tests include sputum smear (KOH test), sputum culture, serum coccidioides complement fixation titer, CBC with differential (shows elevated eosinophils), chest X-ray, and coccidioidin or Spherulin skin test. The acute disease is almost always benign and goes away without treatment. Bed rest and treatment of flu-like symptoms until the fever disappears may be recommended. Amphotericin B is used for progressive disease.

Pulmonary asbestosis is a respiratory disease caused by inhaling asbestos fibers; this results in pulmonary fibrosis. Asbestos-related disease includes pleural plaques (calcification), malignant (cancerous) tumors called mesotheliomas, and pleural effusion. Cigarette smoking increases the risk of developing the disease. Symptoms include shortness of breath on exertion, cough, tightness in the chest, chest pain, nail abnormalities, or clubbing of fingers. Tests include auscultation of the lungs (revealing crackling), chest X-ray, pulmonary function tests, and CT scan of the lungs. Although there is no cure, supportive treatment of symptoms includes respiratory treatments to remove secretions from the lungs by postural drainage, chest percussion, and vibration.
Correct answer:
Azithromycin

Explanation
Azithromycin is a macrolide antibiotic that is highly effective in the treatment of Legionella infections. Legionella is an intracellular pathogen; therefore, antibiotics used to treat it must be able to achieve high intracellular concentrations. Azithromycin is more effective than erythromycin, an alternative therapy. The quinolone antibiotics may also be used to treat Legionella infections and are preferred in the management of transplant patients.

Metronidazole was first introduced in 1959 as an effective treatment for Trichomonas vaginalis infections. Since then, it has been found to be an effective antibiotic in the treatment of anaerobic infections, various parasitic infections, Treponema pallidum, and Campylobacter fetus. Resistance to metronidazole is rare to develop. The antibiotic enters the cell of the bacteria where a reduction of the nitro group of the drug results in the production of compounds that are toxic to the cell wall. It is considered the first drug of choice in the treatment of Clostridium difficile infections.

Vancomycin was first isolated from Streptomyces orientalis. It was introduced in 1958 for the growing problem of penicillin-resistant staphylococci. By 1960, it was superseded by methicillin. In the last 10 years, the use of vancomycin has significantly increased due to the emergence of methicillin-resistant Staphylococcus aureus (MRSA), Clostridium difficile, and enterococcal disease. The antibiotic complexes to the D-alanyl-D-alanine portion of the growing cell wall and inhibits peptidoglycan and transpeptidation. Vancomycin is poorly absorbed orally and thus is given by IV. It is widely distributed throughout the body. Adverse reactions are not common; however, ototoxicity is a serious concern and blood levels must be monitored. Vancomycin is the second drug of choice for the treatment of Clostridium difficile infections.

The mechanism of action of penicillins is through penicillin-binding protein (PBP) binding with subsequent inhibition of transpeptidation reaction and activation of the autolytic enzymes. Administration is orally and IM or IV. Food interferes with absorption, so it should be given 1 hour before or 2-3 hours after meals. Penicillin is widely distributed in the body, but there is poor penetration in some spaces such as the eyes, pericardium, and cerebral spinal fluid. The antibiotic is considered non-toxic, but it can cause allergic reactions in 3-10% of the patient population. Penicillin is most active against Streptococcus spp., Neisseria gonorrhoeae, Treponema pallidum, and Listeria spp. It is used clinically to treat syphilis, Streptococcus pyogenes pharyngitis, and as a prophylactic agent after rheumatic heart disease. Legionella frequently produces β-lactamase, so penicillin is not a good choice for treatment of Legionella.

Cefazolin is a first-generation cephalosporin. It is effective in the treatment of gram-positive infections such as staphylococcus and streptococcus, and it is frequently used as prophylaxis against surgical site infections. Legionella frequently produces β-lactamase, so cefazolin is not a good choice for treatment of Legionella.
Correct answer:
Vibrio cholera

Explanation
This patient's clinical picture is suggestive of cholera. Cholera is caused by Vibrio cholerae, which is a small, Gram-negative bacillus that produces an enterotoxin, which stimulates adenylate cyclase, resulting in increased secretion of fluids and electrolytes.

Cholera is spread by ingestion of water, seafood, and other foodstuffs contaminated by the feces of symptomatic or asymptomatic food handlers. It is endemic in parts of Asia, the Middle East and Africa, but persons living in these areas gradually acquire a natural immunity. There is increased susceptibility to infection in persons with hypochlorhydria and achlorhydria or taking antacids, as the bacilli are sensitive to gastric acid. The incubation period is 1 to 3 days. Patients usually present with painless and profuse watery diarrhea and vomiting of sudden onset. The resultant severe water, sodium, chloride, bicarbonate, and potassium depletion, results in intense thirst, muscle cramps, hypovolemia, oliguria, and anuria with severe metabolic acidosis. If untreated, it can result in circulatory collapse. Uncomplicated cholera is self-limiting, and recovery occurs in 3 to 6 days. Severe cases have a high mortality rate, which is usually due to dehydration.

The diagnosis is confirmed by isolation of V. cholerae in cultures from direct rectal swabs or fresh stools, and its subsequent identification as serogroup 01 or 0139 through agglutination by specific antiserum.

The treatment is intravenous replacement of fluids and electrolytes, such as potassium, with correction of metabolic acidosis. Early treatment with an effective oral antimicrobial eradicates the V. cholerae, reduces stool volume, and stops diarrhea within 2 days. Drugs effective for susceptible strains include tetracycline, doxycycline, erythromycin, trimethoprim-sulfamethoxazole, and norfloxacin. Most patients are free of V. cholerae within 2 weeks, but a few become chronic biliary tract carriers. To control cholera, human excrement must be properly disposed of, and water supplies must be purified. Drinking water should be boiled or chlorinated, and vegetables and fish should be cooked thoroughly.

Patients with staphylococcus aureus food poisoning present with severe abdominal pain and severe vomiting of sudden onset, usually 2 to 8 hours after ingestion of the foodstuffs, which are usually meat and dairy products.

Patients with bacillus cereus food poisoning present with sudden onset vomiting usually 2 to 8 hours after ingestion of the contaminated food. This type of food poisoning is commonly associated with ingestion of reheated fried rice.

Escherichia coli serotype O157:H7 infection usually begins acutely with severe abdominal cramps and watery diarrhea, which may become grossly bloodstained within 24 hours. This type of food poisoning is associated with ingestion of raw beef, unprocessed milk, and dirty water.

Vibrio parahaemolyticus food poisoning is associated with ingestion of saltwater seafood. The patients usually present with fever, vomiting, and severe diarrhea.

Patients with bacillus cereus food poisoning present with the sudden onset of vomiting; symptoms typically start 2 to 8 hours after ingestion of the contaminated food. This type of food poisoning is commonly associated with ingestion of reheated fried rice.

Escherichia coli serotype O157:H7 infection usually begins acutely with severe abdominal cramps and watery diarrhea; the diarrhea may become grossly bloodstained within 24 hours. This type of food poisoning is associated with ingestion of raw beef, unprocessed milk, and dirty water.
Correct answer:
The patrons acquired the illness from the cats

Explanation
The correct response is the patrons acquired the illness from the cats.

The protozoan Toxoplasma gondii infects humans via broken skin, the gut, and the lungs. The definitive host, the cat, excretes oocysts; however, eating poorly cooked infected meat is probably as prevalent as contact with cat feces. Toxoplasmosis is distributed worldwide, but it is common in the tropics. Infection is lifelong. Congenital toxoplasmosis may induce abortion. The fact that cats at the ranch where people became ill tested positive for elevated toxoplasmosis titers while cats from the ranch where no toxoplasmosis cases were reported supports the deduction that cats were the vector for this disease.

The vast majority of infections are asymptomatic. Symptomatic-acquired toxoplasmosis resembles infectious mononucleosis; it is usually self-limiting and lasts a few months. The symptoms are not particularly characteristic; they are generally limited to fever, lymphadenopathy, and headache.

Ocular infection presents with posterior uveitis, which causes blurring and ache; it often occurs in the 2nd decade of life. Encephalitis and myocarditis occur only rarely, except in an immunocompromised (e.g., AIDS) host, in which it may be fatal. Both sexes are susceptible to toxoplasmosis. Although 20 of the 34 infected persons were women, this is not evidence enough to deduce that women are more susceptible, as there is no information given about the number of each sex that were exposed to the illness.

The diagnosis is through a 4-fold rise in antibody titer over 4 weeks, or the presence of specific IgM, which implies an acute infection. The 'dye test' was the 1st serological test available. Parasite isolation is difficult, but a lymph node or brain biopsy may be diagnostic.

It is often self-limiting without treatment. If the eye is involved, or if the patient is immunocompromised, pyrimethamine should be used along with sulfadiazin
Correct answer:
Staphylococcus aureus

Explanation
The causative agent of food poisoning in this case is Staphylococcus aureus. S. aureus is a Gram-positive, aerobic, circular (cocci) organism that appears to be in pairs or in grape-like clusters on microscopic examination. S. aureus is found as normal human body flora colonized in the nasal passages. The organism is pathogenic, pertaining to its ability to produce and release toxins. It is resistant to high salt concentrations, especially sodium chloride (NaCl) and grows on mannitol salt agar forming large, yellow-colored colonies. S. aureus grows well in a temperature range of 15 to 45°C. The majority of the strains of S. aureus show positive results for coagulase test, but it is not a differential diagnostic test to detect the organism, as few strains of S. epidermidis also show positive results for the test. S. aureus is resistant to penicillin and methicillin. Individuals with S. aureus food poisoning have loss of fluid due to diarrhea; therefore, they are advised to drink plenty of water and electrolyte solutions. The preventive measures include proper washing of hands and maintaining good hygiene when preparing or handling foods.

Clostridium perfringens is a Gram-positive, anaerobic, spore-forming bacilli (rod shaped). C. perfringens is commonly found as a soil microorganism. It is also found in the feces of infected persons and thus becomes a source of infection. C. perfringens food poisoning is due to the ingestion of the organism and is associated with intense abdominal cramps and diarrhea. The diagnostic tests include stool examination to detect the toxin or the organism in the infected person's feces. The organism can grow in a wide range of temperatures, and it is cultured in anaerobic liquid media in laboratories. There is no specific treatment for C. perfringens food poisoning, but the preventive measures include cooking food at high temperatures, rapid cooling of cooked foods, and hygienic handling of foods.

Enterococcus faecalis, previously known as Streptococcus faecalis, is a Gram-positive, circular, facultative anaerobe. It is a normal inhabitant of the intestinal tract and female genital tract. It may cause endocarditis, urinary tract infections, bacteremia, wound infections, catheter-related infections, and intra-abdominal/pelvic infections.

Escherichia coli are a common flora of the human body and are generally found in the gut of humans. E. coli are Gram-negative, non-spore forming bacilli. Most strains of E. coli are non-pathogenic, but strains called enterohaemorrhagic E. coli (EHEC) are responsible for foodborne illness due to the toxins they release. The symptoms include abdominal cramps and diarrhea, which may lead to hemorrhagic colitis. The organism grows in a temperature range of 7 to 50°C, but the optimum temperature at which the organism grows best is 37°C. Diagnosis of the infection is generally by microscopic examination of the stool from the infected person. Preventive measures include practicing hygiene when preparing food and using boiled and cooled water for consumption.

Salmonella species are non-spore forming, Gram-negative bacilli. Salmonella are found in the intestinal tract of humans and other warm and cold-blooded animals. They are responsible for causing acute gastroenteritis as a result of foodborne ingestion or intoxication. They are transmitted to the humans via contaminated water and food. Salmonella typhi and Salmonella paratyphi are responsible for typhoid and typhoid-like fever in humans. Measures to prevent infection include hygienic practices when handling food.
Correct answer:
Candidiasis

Explanation
Candidiasis occurs because of overgrowth of this group of yeasts in particular areas of the skin, those that are chronically wet, and especially in the intertriginous zones of the groin and beneath pendulous breasts. Patients with diabetes, chronic intertrigo, and cellular immune deficiency (as in HIV) are particularly susceptible. Obese patients have more intertriginous areas and are thus at risk. The rash is said to be macerated (displaying a waterlogged or soaked appearance characteristic of the dead surface skin). It is also described as erythematous, with marked inflammation, and it may be in a "satellite lesion" distribution, i.e. smaller lesions a few cm out from the larger one, which the "satellites" appear to orbit. The lesions may show scaling, and skin scrapings will show pseudohyphae and yeast forms.

The rash of secondary syphilis can indeed manifest as moist pink lesions in the intertriginous regions. This occurs in about 10% of patients with secondary syphilis and the lesions are called condylomata lata. Secondary syphilis is not the best answer, however. Syphilis is notorious for masquerading as other diseases, but there are certain clues to look for that are more typical of syphilis. The rash, which may be subtle, usually manifests as symmetric mucocutaneous lesions with some truncal distribution. Furthermore, nontender generalized lymphadenopathy is usually present, and the primary chancre of syphilis will still be present in about 15% of patients with secondary syphilis. Finally, RPR should be positive in a patient with secondary syphilis. Other factors to consider are the patient's obesity, diabetes, reports of vulval pruritus consistent with candidal vulvovaginitis and positive HIV status. In summary, secondary syphilis would be an appropriate consideration in this patient, but it would not be the best answer. Of parenthetical note, IV drug users have a high (upwards of 25%) false positive rate by reagin-type tests such as RPR.

Psoriasis is a very common chronic inflammatory condition of the skin. The lesions are variably pruritic and are characterized by sharply demarcated papules and rounded plaques. A silvery scale is frequently observed covering the erythematous plaques. Depending on the distribution and character of the lesions, psoriasis can be further categorized into several sub-groupings. The most common subtype (plaque type) of psoriasis is usually distributed on the elbows, knees, sacral area/gluteal cleft, and scalp, but there is also a less common variety known as inverse psoriasis. This is where the plaque lesions form in intertriginous regions in addition to scalp, palms, and soles. Because of the moisture in the intertriginous areas, scales may not be evident. Other forms of psoriasis include eruptive or guttate psoriasis as well as some variants where the lesions are more pustular in character. The etiology of psoriasis is not well defined, but there may be some association with certain medications, such as lithium and beta-blockers.

Atopic dermatitis is the skin's reaction to allergy (food, asthma, animal dander, etc.). In children and adolescents, it is frequently localized to the flexural skin creases of the antecubital and popliteal fossae. Skin injury is more often a result of scratching than of the atopic process itself, and these individuals have a higher incidence of Staphylococcus aureus skin infections than do unaffected patients. Patients with atopic dermatitis are advised to avoid irritants and to keep skin moist (which includes avoiding hot showers and profuse scrubbing). Treatment often includes the judicious use of low-dose topical glucocorticoids and conservative administration of antihistamines to reduce the itching.

Intertrigo is not one of the listed answer choices, but discussion here may be helpful. Stedman's Medical Dictionary (26th edition) defines intertrigo as: "irritant dermatitis occurring between folds or juxtaposed surfaces of the skin, as between the buttocks, between the scrotum and the thigh, beneath pendulous breasts, etc., caused by friction, sweat retention, moisture, warmth, and concomitant overgrowth of resident microorganisms, and occurring in young children and obese adults." As such, a patient with intertrigo could indeed have candidiasis, but a patient with candidiasis does not necessarily have intertrigo.

Lichen planus is a condition that produces primary lesions described as pruritic, polygonal, flat-topped violaceous papules. Lesions may show thin grey lines (Wickham's striae), and they have a tendency to occur on wrists and shins, but can occur anywhere on the skin. Mucous membranes including the buccal mucosa can be involved. The etiology is not completely understood, and the course is variable, but the lesions usually disappear spontaneously within several months to 2 years. Treatment may include topical glucocorticoids.

Here is a list of each of the possible answer choices together with a simplified association:

Atopic dermatitis—allergic, flexural creases
Candidiasis—diabetic, chronic intertrigo
Lichen planus—pruritic polygons
Psoriasis—silvery scaled papules and plaques
Secondary syphilis—the masquerader
Correct answer:
Measles

Explanation
Prior to the onset of the rash of measles, there is a fever, an upper respiratory infection, and Koplik's spots. Koplik spots are blue-gray spots that can be seen in the mouth. The rash is a maculopapular rash that may become confluent. Typically, the rash begins on the face and moves downward and outward over the whole body. The rash can go to the hands and feet. A patient with measles can have associated cough, adenopathy, and high fever. Winter and spring are the typical times of year for measles to occur.

Hand-foot-mouth disease is a disease that occurs in children. The rash associated with hand-foot-mouth disease consists of vesicles on a reddened base. The hands and feet are the most common body parts affected. Oral ulcers or vesicles can be seen. Fever sometimes occurs with the other symptoms. Coxsackie virus is the etiologic agent of hand-foot-mouth disease. The typical time for hand-foot-mouth disease to occur is the summer and fall.

Kawasaki disease is a disease that occurs in children. There is a high fever before the onset of the rash. The rash seen with Kawasaki disease is erythematous with desquamation. The entire body can be affected by the rash. Winter and spring are the typical times for Kawasaki disease to occur.

Toxic shock syndrome is caused by a toxin produced by Staphylococcus aureus. There is accompanying high fever and hypotension. There is no predilection for a particular season.

Rocky Mountain spotted fever is transmitted by ticks. With Rocky Mountain spotted fever, there is a fever, headache, and malaise. The wrist, ankles, palms of the hands, and soles of the feet are initially affected. The trunk can also be affected. Rocky Mountain spotted fever is caused by Rickettsia rickettsii. April through September is the typical time frame for Rocky Mountain spotted fever to occur.
Correct answer:
Clostridium tetani

Explanation
Clostridia are anaerobic spore-forming Gram-positive rods that produce an array of toxins. Clostridium tetani spores are ubiquitous in soil, and are introduced into tissues by a puncture wound caused by a contaminated object. In the anaerobic environment of traumatized tissues, C. tetani spores germinate; vegetative cells produce toxins and proteolytic enzymes that contribute to a rapid development of necrosis. In individuals not protected by vaccination, infection may progress to localized or generalized tetanus. Upon germination of endospores, C. tetani produces a toxin (tetanospasmin) that blocks presynaptic neurotransmitter release, causing rigid paralysis. C. tetani cells have terminal endospores, resulting in a 'drumstick' or 'tennis racket' appearance.

C. perfringens is a common cause of food-borne illness that may also colonize soft tissue and skin. C. perfringens also causes a crepitant cellulitis with gas formation, and a rapidly fulminating and often fatal form of fasciitis. C. perfringens can be differentiated from C. tetani microscopically by its centrally located endospores and lack of motility.

C. botulinum also causes food-borne illness, often as a result of home or commercially-canned foods. As bacteria grow and lyse, they release botulinum toxin. When reaching peripheral cholinergic synapses, botulinum toxin prevents release of acetylcholine and causes a flaccid paralysis. C. botulinum can also cause wound infections, but this organism is less invasive than C. tetani. Microscopically, the presence of subterminal endospores distinguishes this C. botulinum from C. tetani.

C. difficile is a frequent cause of antibiotic-associated colitis; it produces subterminal endospores.

Bacteroides fragilis is present among normal flora; it is the most frequent cause of suppurative anaerobic infection. Bacteroides are Gram-negative; they do not produce endospores.
Correct answer:
Pasteurella multocida

Explanation
The majority of infections involves skin and subcutaneous tissue. Rapid onset of wound infection and development of cellulitis or abscess at the site of the bite is very characteristic. Among the listed zoonotic pathogens, Pasteurella multocida is the only bacterium possessing the described characteristics of the isolate. The bacterium is part of the normal flora of cats, dogs, and other domestic and pet animals. Human infection often follows bite, scratches, or licks from these carrier animals. Increased carriage rates have been observed in cats. Infections following cat bites and scratches are more common.

P.multocida can also cause bacteremia, meningitis, pneumonia, septic arthritis, osteomyelitis, endocarditis, peritonitis, sinusitis, and urinary tract infection. Persons in extremes of age and immunocompromised individuals, including those with liver cirrhosis, renal disease, hematological malignancies, and post-transplant patients, are at risk for more severe invasive disease by P.multocida. P.multocida causes a wide variety of diseases in animals such as fowl cholera in poultry, atrophic rhinitis in pigs, and bovine respiratory diseases and hemorrhagic septicemia in cattle. Key virulence factors of P.multocida are its capsule and lipopolysaccharide. Some strains associated with atrophic rhinitis in pigs are toxigenic. ToxA gene, the structural gene for P.multocida toxin (PMT), resides in a prophage. Antibiotics including beta-lactams, tetracyclines, and fluoroquinolones are used for treating P.multocida infections. Clindamycin and erythromycin are not recommended. Beta-lactamase producing P.multocida strains have been reported from human infections, though very rarely.

Bartonella henselae, the agent of "cat scratch disease" (CSD), is a fastidious Gram-negative bacterium, and cultural isolation on chocolate agar requires a minimum of 3 weeks of incubation. It gives negative catalase, oxidase, and carbohydrate utilization tests. CSD is often self-limited. Typical clinical presentation is fever and lymphadenopathy developing about 2 weeks after contact with a cat. B.henselae is associated with bacillary angiomatosis also.

Ehrlichia chaffeensis causes human monocyte ehrlichiosis and is transmitted by ticks. E.chaffeensis and Coxiella burnetii, the organism of Q fever, are strictly intracellular and fail to grow on cell-free media. C.burnetii is transmitted among animals by ticks. Humans acquire infection mostly by inhalation of contaminated aerosols and also by drinking unpasteurized milk.

Bordetella bronchiseptica occurs as commensals in the upper respiratory tract of many wild and domestic animals. The bacterium is motile with peritrichous flagella. Human infections are very rare.
Correct answer:
Single IM dose of penicillin G benzathine

Explanation
The correct response is single IM dose of penicillin G benzathine.

Primary syphilis is indicated by an indurated, painless chancre on the penis. The chancre is a disease hallmark. Syphilis is caused by the spirochete Treponema pallidum, and it is transmissible during early disease through exposure to open lesions rich in spirochetes. Non-sexual infection is rare, but it can occur through personal contact, blood transfusions, and accidental inoculations. Primary syphilis develops within several weeks of exposure and involves 1 or more painless chancres. Secondary syphilis develops after the chancre is healed, and patients develop clinical illness associated with malaise, anorexia, headache, lymphadenopathy or rash. Diagnosis is established by serologic tests (RPR or VDRL). Tertiary syphilis is associated with cardiovascular, neurologic, and systemic symptoms.

The incubation period of syphilis is 10 - 90 days, and symptoms usually develop within about 3 weeks after exposure. The patient indicated sexual contact with the prostitute 3 days ago, so the patient probably contracted the disease from his wife.

The drug of choice for primary syphilis in immunocompetent hosts is single-dose penicillin G benzathine, given IM. If the disease duration is greater than 1 year, 3 doses of penicillin G IM should be given 1 week apart. Alternatives include doxycycline or erythromycin for 14 days. Intravenous penicillin is not indicated in primary syphilis, but it is used in neurosyphilis, where it is administered for 14 days.

Single dose azithromycin is a first-line treatment for gonorrhea, but it is not used in syphilis management.

Biopsy of the lesion is not required because dark-field microscopy of the lesion exudate is used to visualize spirochetes confirming the diagnosis. Because dark field microscopy is time consuming and a specialized skill, serologic tests such as RPR or VDRL are preferred.

Lumbar puncture (LP) is not indicated in primary syphilis. LP is indicated when neurologic or ophthalmic signs and symptoms are present, and cerebrospinal fluid (CSF) data should be correlated with cardiovascular, neurologic, and systemic symptoms.
Correct answer:
Bacillus cereus

Explanation
Despite vast improvements in sanitation, food-borne illnesses remain a fairly common occurrence. Prompt laboratory investigation is required in order to establish the diagnosis. This usually only occurs when a relatively large number of individuals simultaneously experience a similar constellation of symptoms after having consumed a common food source. Therefore, many cases of food-borne illness often go undiagnosed. Several infectious sources are associated with food-borne illness. The clinical symptoms associated with them demonstrate significant overlap, yet several of the most common causes have distinguishing features.

Bacillus cereus is an organism that causes illness via the production of enterotoxins. 2 enterotoxins are produced by these spore-forming bacteria, 1 that is heat stable and another that is inactivated by heat (heat labile). The heat stable species causes primarily vomiting, whereas the heat labile form results predominantly in diarrhea. Intoxication caused by Bacillus cereus is most commonly associated with foods - classically rice - that have been reheated after having been left at room temperature. Illness usually occurs within a few hours of ingestion and usually resolves within 24 hours.

Staphylococcus aureus produces illness indirectly via a specific enterotoxin. Patients present with rapid onset of symptoms, usually within 30-60 minutes of ingestion. Patients typically experience nausea and cramps followed by vomiting. Duration of symptoms is short, usually 24-48 hours. Since humans are the principal reservoir for Staphylococcus, uncooked foods that require extensive handling, such as salads, eggs, dressings and sandwich meat, are the most common sources. Staphylococcus aureus also causes dermatologic lesions, such as pustules and abscesses; when present on the skin of food handlers, they can be a source of contamination. In addition, Staphylococcus aureus is present in cows; therefore, milk and cheese products that are not adequately refrigerated can also cause illness.

Clostridium perfringens is also a toxin-producing organism. Cramping and diarrhea are the most common symptoms of illness caused by C. perfringens. Nausea also occurs, but vomiting is rare. Inadequately heated meat products are the most common source. Onset of symptoms occurs within 12 hours of ingestion, and symptoms usually abate in a day.

Giardia lambliais a protozoon that causes upper intestinal enteritis marked by fatigue, chronic diarrhea, steatorrhea, colicky abdominal pain, and bloating. Infection can occur with ingestion of a single cyst, and symptoms generally appear within 1 week of exposure. Fecal contamination of drinking water is a common source of infection, as is person-to-person infection via hand-to-mouth contact with the feces of an infected individual. This method has caused outbreaks to occur in institutional facilities such as day care centers. Diagnosis of Giardia lamblia can be made by visualization of trophozoites or cysts in appropriately prepared fecal specimens.

Although often asymptomatic, infection with the Entamoeba histolytica protozoan can produce a host of intestinal syndromes, the most severe of which is acute dysentery marked by fever, chills, and bloody or mucoid diarrhea. Less severe colitis, indistinguishable from other causes of inflammatory bowel disease, can also occur, making the diagnosis of amebiasis difficult. In addition to intestinal illness, Entamoeba histolytica can also cause liver abscesses. As with giardiasis, fecally contaminated food or water is the most common method of transmission.
Correct answer:
Roseola

Explanation
This child exhibits the typical rash of roseola. Roseola infantum (also called exanthem subitum) is caused by Human Herpesvirus-6 and occurs almost exclusively during infancy. There is usually no prodromal period. The illness begins with high temperatures (averaging 103 F) for 3 to 5 days; the fever typically resolves rather abruptly. The rash appears within 12 to 24 hours of the fever resolution. The rash of roseola is rose-colored and begins as discrete, small, slightly raised pink lesions on the trunk and spreads to the neck, face and proximal extremities. The rash is not pruritic and no vesicles or pustules develop. The lesions may become confluent. Roseola is self-limited and the treatment is supportive only (e.g., antipyretics during the febrile phase).

Rubella differs from roseola in that it has a distinct prodromal period, with prominent occipital and postauricular lymphadenopathy, and the low-grade fever is coincident with the rash. Measles (rubeola) is caused by a paramyxovirus and is manifested by cough, coryza, conjunctivitis, and Koplik's spots. The rash associated with measles is generalized, maculopapular, and erythematous, and occurs at the height of the fever. Drug hypersensitivity is a common condition that resembles roseola. Antibiotics are often given during the initial febrile phase of roseola before the rash appears. The rash associated with drug hypersensitivity is morbilliform and pruritic; it disappears after the offending drug is discontinued. Varicella (chickenpox) is caused by a human herpes virus and is still seen despite the availability of a vaccine. Often, there is a prodrome of fever, malaise, headache, anorexia, and mild abdominal pain 24 to 48 hours before the rash. The lesions start on the scalp, face, or trunk, and they consist of intensely pruritic erythematous macules that develop to form clear, fluid filled vesicles. The lesions then umbilicate and crust over while new crops form elsewhere on the body.
Correct answer:
Ceftriaxone 250 mg IM plus azithromycin 1g PO each single dose

Explanation
The correct response is ceftriaxone 250 mg IM plus azithromycin 1g PO each single dose.

This patient has gonococcal urethritis, which is evidenced by the diplococci in the urethral discharge. The causative organism of gonorrhea is Neisseria gonorrhoeae, which is a Gram-negative intracellular diplococcus. It is most commonly seen in people between 15 and 29 years old. It is usually transmitted during sexual activity, and it has increasing incidence in homosexual men. Multiple sexual partners, unprotected intercourse, and anal sex are important risk factors. The incubation period of Neisseria gonorrhoeae is 2 - 8 days. Other than urethritis, it can also cause epididymitis, prostatitis, proctitis, cervicitis, vaginitis, and salpingitis. Pharyngeal infection is atypical, but it is not uncommon. Disseminated disease is associated with fever, rash, arthritis, and tenosynovitis. Chronic infection can cause urethral strictures, chronic salpingitis, infertility, and chronic prostatitis. Asymptomatic infection is quite common and can occur in men and women. Chronic cervicitis is an important reservoir of infection. Gram stain of the urethral discharge shows Gram-negative diplococci inside neutrophils. The gold standard is a positive culture from any site, including the urethra, cervix, pharynx, and rectum. DNA probes can be used for urethral and endocervical specimens. Nucleic acid amplification tests are available for testing urine and urethral specimens. Testing urine in the office is quite popular with patients and staff because it is noninvasive, fairly sensitive, and specific. Such patients have a high frequency of co-infection with chlamydia; therefore, treatment for both is given at the same time. Ceftriaxone plus azithromycin is given for gonococcus, and azithromycin or doxycycline are the recommended regimens for Chlamydia.

Erythromycin base, erythromycin ethylsuccinate, levofloxacin, ofloxacin, or doxycycline are acceptable alternatives to azithromycin for nongonococcal urethritis (NGU) only, but there is a distinct possibility of noncompliance with a 7-day course.

A 3-day course of trimethoprim-sulfamethoxazole is suitable only for uncomplicated cystitis in women, and it would be useless in urethritis in men.

Ceftriaxone alone does not cover chlamydial infections.
Correct answer:
Botulism

Explanation
The most likely diagnosis is infant botulism; the 6-month-old infant was previously healthy and developed poor feeding, constipation, lethargy, weak cry, drooling from the mouth, ptosis, and weak gag and corneal reflexes; those symptoms were followed by descending paralysis, starting with loss of head control, weakness of upper limbs, trunk, and then lower limbs. Blood counts and CSF were normal, which excludes sepsis. The classical triad of botulism is symmetric flaccid descending paralysis, beginning with cranial nerve musculature with clear sensorium, no fever, and no paraesthesias. Nerve conduction velocity and sensory nerve functions are normal in botulism. Human botulism has 3 naturally occurring forms:

Infant botulism is the most common in USA.
Food borne botulism occurs in older children and adults due to ingestion of food contaminated by botulinum toxin through improperly canned or preserved food, honey, or corn syrup.
Wound botulism occurs due to colonization of traumatized tissue by Clostridium botulinum.
Ingestion of honey is a risk factor for infant botulism.

The clinical features of botulism are caused by a neurotoxin produced by Clostridium botulinum, which is a gram-positive, spore forming, obligate anaerobe naturally present worldwide in soil, dust, and untreated water. Botulinum toxin is carried by the blood stream to peripheral cholinergic synapses, where it binds irreversibly, blocking acetyl choline release and causing impaired neuromuscular transmission.

Tick paralysis is a disorder of acetylcholine release and occurs due to a neurotoxin produced by the wood tick or dog tick. These arachnids are common in the Rocky Mountains of North America. The tick embeds its head in the skin, usually of the scalp, and starts producing the neurotoxin. It affects large myelinated motor and sensory nerve fibers. Motor symptoms include weakness of muscles and loss of coordination. Sometimes, it may produce ascending paralysis resembling Guillain-Barre syndrome. Tendon reflexes are lost. Parasthesias may occur over the face and extremities. Diagnosis is confirmed by identifying the tick. The tick must be removed completely along with the embedded head beneath the skin. The patient then recovers completely within a few hours or few days.

Spinal muscular atrophy (SMA) is an autosomal recessive disorder and manifests as generalized symmetrical muscle weakness more in proximal muscle groups, hypotonia, and fasciculations of the tongue. Trunk muscles are commonly involved, and the infant is never able to sit. The infant has poor feeding and a weak cry. Weakness of the lower limbs is greater than the upper limbs. Deep tendon reflexes are lost. Fibrillations and fasciculations are reported on EMG. SMA type1 (Werdnig-Hoffman disease) presents during the first 6 months of life. Disease is progressive, and most patients die by 10 years of age. SMA types II, III, and IV occur later in life.

Myasthenia gravis is an autoimmune disorder characterized by rapid fatigue of striated muscles. It can occur during the first few days after birth in infants of myasthenic mothers. Placental transfer of ACh R-antibodies results in transient impairment of neuromuscular transmission in the neonate. Symptoms include poor sucking and swallowing, weak cry, ptosis, decreased movements of the limbs, generalized weakness, and hypotonia. Symptoms usually resolve in 4 weeks or may persist for months. Juvenile myasthenia gravis is usually present after 10 years of age. Clinical features include ptosis, facial, and oropharyngeal weakness, resulting in dysarthria, dysphagia, and difficulty in chewing. Proximal muscles of the limbs are more involved. Weakness improves after sleep or resting and is worsened by exertion. It can occur at any age, but is most common in people of both sexes between 30-50 years of age.

Guillain-Barre syndrome is an autoimmune process and is characterized by symmetric weakness of muscles starting from the lower limbs and then ascending to the trunk and upper limbs. Pain in the muscles may occur early in the course of illness. In 2/3 of cases, there is a preceding history of viral illness 2-4 weeks prior to the onset of neurological symptoms. Weakness is more marked in proximal muscle groups. There is hypotonia with diminished deep tendon reflexes. Facial nerve involvement occurs in 3/4 of cases. In 80% of patients, CSF shows raised proteins (>45 mg/dL) with a normal cell count.
Correct answer:
TB culture

Explanation
The correct response is TB culture.

Tuberculosis (TB) is a chronic mycobacterial infection that most commonly affects the lungs but potentially can spread to other organs of the infected individual. TB is usually spread person to person via droplets after a cough or a sneeze. TB can be actively infectious, but also may have a latent phase; this is when the patient has the TB mycobacteria in his/her body does not have symptoms of the disease. There is are many groups of patient who have a higher risk of developing a TB infection, including those who live/work around people who have TB, medically underserved populations, and patients that may reside in more of a group setting, such as a nursing home or jail.

Symptoms of TB initially may be just a nonproductive cough; as the disease is allowed to progress to hemoptysis. Other signs and symptoms may include chest pain, fatigue, loss of appetite, unintentional weight loss, fever, and chills or night sweats.

To confirm the diagnosis of TB, a TB culture should be ordered and completed. An acid-fast bacilli (AFB) smear is usually completed to help support the diagnosis of TB, but it cannot by itself indicate diagnosis as other bacterial may display all positive result. AFB smear may also be used to monitor treatment of TB once it has been initiated.

Tuberculin skin test, also known as purified protein derivative (PPD) or Mantoux test, is administered intradermally to test for prior exposure to TB. However, PPD testing cannot indicate active or latent/dormant TB.

A chest radiography will often only demonstrated results of an acute granulomatous infection (Ghon complex) and again, does not confirm diagnosis.

QuantiFERON-TB Gold is a whole-blood test that can detect TB in those patients recently exposed or who are suspected to have a TB infection; however, this test does not indicate if the TB infection is active or latent.
Correct answer:
Infectious mononucleosis

Explanation
The most common symptoms of infectious mononucleosis, which is caused by the Epstein-Barr virus (EBV), are pharyngitis, fever, and lymphadenopathy. It is frequently diagnosed in adolescents and young adults, and it is more common in settings such as high school or college. Approximately 1/2 of all patients have splenomegaly. These symptoms, combined with T-cell lymphocytosis, are highly suggestive of mononucleosis. The diagnosis can be confirmed with the 'monospot' test which shows the presence of heterophil antibodies. Fever may persist for 14 days or longer. Most patients recover within 3 to 4 weeks, but some experience malaise for months.

The usual course of Streptococcal pyogenes pharyngitis is the resolution of symptoms after 3 to 5 days. A throat culture is the gold standard for this diagnosis.

Influenza is characterized by an abrupt onset. In addition to the symptoms described above, patients frequently have myalgia and respiratory complaints such as cough and postnasal discharge. It usually resolves within 5 days.

The most common clinical symptom of mycoplasmal pneumonia is acute or subacute tracheobronchitis. Crackles or wheezing may be heard, and patients may have small pleural effusions.

Primary infection with HSV-1 can cause pharyngitis, and it usually results in ulcerative lesions of the posterior pharynx and/or tonsils. HSV antigens can be isolated in scrapings from the lesions. In 1/3 of cases, concomitant lesions of the tongue, buccal mucosa, or gingiva may occur in the course of HSV infection.
Correct answer:
Lyme disease

Explanation
Lyme disease is the most likely diagnosis given the arthritic clinical picture and history of backpacking in an endemic area. 90% of Lyme disease in the United States occurs in the Northeast or upper Midwest (New York, New Jersey, Connecticut, Rhode Island, Massachusetts, Pennsylvania, Wisconsin, and Minnesota).

Classically, Lyme disease consists of 3 stages:

Stage 1 features flulike symptoms (arthralgia, headache, malaise, and weakness) and the typical single skin lesion of erythema migrans (EM) or "bull's-eye" rash at the site of the tick bite.
Stage 2, after a latent period, features a rash similar to the one described here and systemic symptoms similar to those of stage 1.
Stage 3, after a varying prolonged asymptomatic period that ranges from months to years, features synovitis, arthritis, central nervous system impairment, dermatitis, keratitis, as well as neurologic and myocardial abnormalities.
It is important note that a great percentage of cases do not follow this neatly described sequence. Moreover, a significant proportion of afflicted patients give no history of a tick bite.

Pityriasis rosea is incorrect. Pityriasis rosea is a harmless pruritic, scaly skin disease that is often found in people 10 - 35yrs of age. Initially, most people develop 1 large scaly 'herald patch'; within 1 - 2wks, smaller pink patches can occur on the trunk, arms and legs.

Rocky Mountain spotted fever is incorrect. RMSF is a tick-borne disease caused by the bacterium Rickettsia rickettsii. It is a potentially fatal illness that occurs in North and South America; it is characterized by nausea, vomiting, fever, headache, and abdominal pain. It can have a maculopapular skin rash in the late phase of the disease.

Secondary syphilis is incorrect. The skin rash of secondary syphilis is typically characterized by symmetrical, reddish-pink, non-itchy papules, and nodules on the trunk and extremities, including the palms and soles.

Pityriasis versicolor is incorrect. Pityriasis versicolor is caused by yeasts of the genus Malassezia, which may also be found on normal skin. It affects the trunk, neck, and/or arms; it is characterized by asymptomatic hypopigmentation in dark-skinned persons and hyperpigmentation in fair-skinned persons.
Correct answer:
Vibrio cholerae

Explanation
Vibrio cholerae is a comma-shaped Gram-negative rod. V. cholerae are oxidase-positive and grow on selective medium (TCBS), allowing their laboratory differentiation from Salmonella, Shigella, and Campylobacter. In patients infected with the cholera agent, stool samples lack leukocytes and show highly motile rods by darkfield microscopy examination. Epidemiologically, cholera should be suspected in a patient with profuse watery diarrhea, a history of travel to an endemic region, and a history of exposure (by consumption) to food or water potentially contaminated with sewage. Illnesses caused by V. cholera exotoxin range from mild abdominal cramping to life-threatening hypovolemic shock. Clinical signs and symptoms include profuse watery diarrhea 12 - 24 hours after exposure, abdominal pain, vomiting, anorexia, apathy, fever, malaise, seizures, and extreme thirst.

Clostridium perfringens, a Gram-positive anaerobic rod, is a common cause of food poisoning in the United States. Vomiting and diarrhea occur 8 - 12 hours after ingestion of a heat-labile toxin, often in association with inadequately reheated meat. Fever is usually absent, and the illness resolves in about 24 hours.

Clostridium difficile is a Gram-positive anaerobic rod that causes pseudomembranous colitis in patients treated with antimicrobials.

Campylobacter jejuni, like Vibrio, is a curved Gram-negative rod. Gastroenteritis caused by C. jejuni occurs worldwide; in the United States, it is more common than gastroenteritis caused by Salmonella and Shigella combined. Fecal-oral transmission is common, particularly when associated with chicken consumption. Clinically, Campylobacter-induced illness differs from that caused by V. cholerae by a more insidious onset and the presence of a high fever and blood in the stool.

Shigella sonnei causes dysentery; it is a significant problem in pediatric populations. Within 24 - 48 hours of ingesting Shigella, the patient often experiences acute onset fever, abdominal cramping, and profuse watery diarrhea. Like Campylobacter, Shigella diagnosis can be aided by the detection of leukocytes in stool specimens.
Correct answer:
Primary stage syphilis

Explanation
Primary stage syphilis is caused by a spirochete called Treponema pallidum; it is characteristically initiated with a generalized bacteremia. This bacteremia occurs within 30 hours after infection. It is a sexually transmitted disease. The multiplication of the Treponema pallidum organism occurs at the site of entry where there is the formation of a "primary chancre." This primary chancre usually appears after an average 21-day incubation period; it quickly erodes and becomes indurated. Regional lymphadenopathy is present consisting of moderately enlarged, firm, nonsuppurative, painless lymph nodes, or satellite buboes. The chancre is described as having a smooth base, with a raised border that is firm. It is generally clean in appearance unless there is a secondary infection present. The chancre is painless but slightly tender to the touch. When obtaining scrapings for analysis, there is little or no pain and bleeding from the chancre. These scrapings are of value because they are generally rich in Treponema organisms that can be seen when observed under dark-field microscopy. The visualization of motile Treponema in scrapings under dark-field examination is diagnostic for Treponema pallidum. Both treponemal and nontreponemal antibodies appear 1-4 weeks after the appearance of the primary chancre. The primary chancre usually heals within 3-6 weeks and usually does not leave any scarring. The lymphadenopathy usually will persist for a longer period of time. Secondary syphilis symptoms will begin to occur often while the primary chancre is still present.

Chancroid is caused by the bacteria Haemophilus ducreyi. It is characterized by one or more painful, exudative, indurated ulcers (associated with a tender lymphadenopathy) that eventually suppurate if untreated. It is a sexually transmitted disease. Haemophilus ducreyi is a small pleomorphic gram-negative coccobacillus with fastidious growth requirements. It is most common in uncircumcised non-Caucasian men, populations of low socioeconomic status, and poor hygienic conditions. The number of reported cases in women is very low; this may be due to a clinically inapparent carrier state, or asymptomatic and overlooked lesions. The organism has an incubation period (exposure to clinical disease) of 1 day to several weeks. The lesions are generally confined to the genital and perianal areas, with lesions on the mouth, fingers, and breasts being very rare. The appearance of multiple lesions (up to 10) is the norm. Detection can be made by culturing for the organism, but most routine clinical laboratories are not equipped for the isolation of this organism.

Primary genital herpes is caused by the herpes simplex virus type 2 (HSV-2). The infection is most common in adolescents and young adults. Incubation periods are generally 2-7 days. Men generally present with vesicular lesions on an erythematous base. These lesions usually appear on the glans penis or the penile shaft. Women generally present with lesions that involve the vulva, perineum, buttocks, cervix, and vagina. Vaginal discharge is frequently reported. These primary infections are often associated with fever, anorexia, tender bilateral inguinal adenopathy, and malaise. The lesions of primary genital herpes may last for several weeks before healing is complete. Urethral involvement may result in dysuria or urinary retention. Detection can be made by viral culture.

Localized candidiasis is most commonly caused by the yeast Candida albicans. Candida albicans is the most common clinically significant yeast isolated. This is an infection more commonly seen in women than men. Generally, the symptoms of localized candidiasis are pruritus, erythema, and a thick and adherent whitish discharge that contains curds. The vaginal pH is normal, as in comparison to the pH of bacterial vaginosis and trichomoniasis where the pH is elevated. The addition of 10% potassium hydroxide to vaginal discharge does not elicit any fishy odor, as is seen with bacterial vaginosis. The diagnosis can be made quickly by performing a KOH prep, which will allow you to visualize the presence of the fungi; however, 30-50% of women with candidiasis will have yeast numbers that are low in the discharge and thus produce false negatives. Culture methods are best utilized for a definitive diagnosis.

The diagnosis of trichomoniasis is established by the presence of pear-shaped trichomonads on wet mount. Most men with this infection are asymptomatic, whereas in women, dysuria and a malodorous discharge are common presenting symptoms.

Anogenital warts are caused by a human papillomavirus (HPV). These viruses produce anogenital warts that are flesh to gray in color, hyperkeratotic, and exophytic papules. The warts are usually attached to the skin by a short broad peduncle, or they may be sessile on the skin. Circumcised men will have these warts occurring on the penile shaft; in uncircumcised men, the warts will commonly appear in the preputial cavity. The urethral meatus is also involved in 1-25% of patients. In the homosexual population, the warts will occur most commonly in the perianal area. The occurrence of warts on the groin, scrotum, pubic area, and perineum is only occasionally encountered. Women are most apt to have the warts distributed over the posterior introitus and over the labia majora, minora, and clitoris. Most patients present with anogenital warts that are asymptomatic, but frequently there is itching and burning, as well as pain and tenderness.
Correct answer:
Shingles

Explanation
The herpes zoster virus causes shingles. It is identical to the varicella virus, which causes chickenpox. Exposure to the varicella virus results in the establishment of a latent state in many individuals. The virus may remain dormant for many years before being activated and expressed as a different disease, shingles. Each year, over 300,000 individuals experience severe episodes of shingles.

There are numerous factors that been attributed to the reactivation of the herpes zoster virus. Exposure to sunlight, chemotherapy, immunosuppression, menstrual cycle changes, trauma, depression, and anxiety are but a few of the factors reported to induce the expression of shingles. Rash-like lesions associated with each episode range from undetectable to severe. Scratching can cause secondary bacterial infections, which exacerbate the situation.

Shingles affects a specific dermatome (portion of the body innervated by a segmental sensory dorsal root ganglion). Fluid recovered from the lesions contains active virus, capable of infecting unexposed individuals. The patient rarely autoinfects with new dermatomal presentation. Both humoral and cell-mediated immune responses restrict the spread of the virus to new body sites, but are unable to eradicate the virus from the body, since it is sequestered in protected ganglia. Interferon may stabilize the infection.

Current treatments do not eliminate the infection. They only reduce the severity of the episode. Hyperimmune globulin is effective in suppressing varicella infections in cases of known exposure. Immunosuppressed individuals are at risk from varicella and would benefit from passive immunization. The attenuated chickenpox (herpes zoster) vaccine, first introduced in 1995, is relatively safe and effective. Prior to the introduction if this vaccine, over 12,000 people were hospitalized annually due to severe cases of chickenpox.
Correct answer:
Mycobacterium marinum

Explanation
Mycobacterium marinum is a mycobacteria. The organism characteristically produces infections that are almost always located on superficial tissues and extremities. These infections are acquired through contact with Mycobacterium marinum-contaminated water; the contaminated water must enter broken or traumatized skin areas. Infection may follow trauma from fish spines or nips by crustaceans. Initial lesions begin at 2 - 3 weeks incubation and appear as small papules that enlarge and acquire a blue-purple hue. Suppuration then occurs and may progress to ulceration. Small nodules may appear in the efferent lymphatics that resemble those seen in sporotrichosis. The organism will grow optimally at 32° C with a growth rate of 7 - 14 days; it is niacin and nitrate-negative and Tween hydrolysis and urease-positive.

Mycobacterium kansasii is a mycobacteria. The organism can produce a chronic bronchopulmonary disease (usually in adults) that closely resembles Mycobacterium tuberculosis. Symptoms are somewhat milder than with Mycobacterium tuberculosis; they are usually present with other underlying pulmonary conditions, such as COPD. Patients usually present with physical findings that are minimal, and most routine tests are normal. There may appear an ESR elevation with slight leukocytosis. The organism has a growth rate of 10 - 21 days, niacin-negative, nitrate-positive, Tween hydrolysis-positive, and urease-positive.

Mycobacterium gordonae is a mycobacteria. The organism is not considered a human pathogen; it only rarely causes disease, and is usually considered a water contaminant. In cases where the laboratory has isolated Mycobacterium gordonae, multiple isolates from multiple patients is indicative of a water contamination problem, either in the media or decontamination procedure. The organism has a growth rate of 10 - 28 days, niacin and nitrate-negative, Tween hydrolysis-positive, and urease-negative.

Mycobacterium avium-intracellulare is a mycobacteria and is often known as MAC. In non-AIDS patients, the disease is generally pulmonary in nature. The clinical manifestations are described as subtle and unobtrusive when other lung disorders are suspect or concomitantly present. 84% of patients will have a cough, 79% will have a productive cough, and 21% will have hemoptysis. Patients generally do not present as being acutely ill, and the features of chronic disease (e.g., anemia, hypoalbuminemia) are often absent. Disseminated disease is rare in non-AIDS patients. In AIDS patients the symptoms are much more acute, with fever, drenching night sweats, and weight loss. Patients will also present with diarrhea, and they will have elevated alkaline phosphatase levels. The organism has a predilection for the reticuloendothelial system and thus causes lymphadenopathy, splenomegaly, and hepatomegaly. Because of the reticuloendothelial system involvement, the isolation of MAC from the blood is frequent, and a diagnostic sign of dissemination. Growth rate is 10 - 21 days, niacin and nitrate-negative, and Tween hydrolysis and urease-negative.

Mycobacterium tuberculosis is a mycobacteria. Mycobacterium tuberculosis, along with Mycobacterium bovis, is the causative agent of tuberculosis. Mycobacterium tuberculosis disease can manifest itself in a variety of infections, but is most commonly seen as pulmonary tuberculosis. Early pulmonary tuberculosis is asymptomatic, and is usually discovered on a chance chest roentgenogram. However, an increase in the bacillary population will produce nonspecific systemic reactions, resulting in anorexia, fatigue, weight loss, and night sweats. As the disease progresses, it is accompanied by chronic cough, sputum production, and, on occasion, hemoptysis. Chest pain will usually develop at this stage, and the patient will then seek medical attention. The organism has a growth rate of 12 - 28 days, is positive for both niacin and nitrate, is Tween hydrolysis-negative, and is urease-positive.

Mycobacterium bovis is a mycobacteria. Mycobacterium bovis, along with Mycobacterium tuberculosis, and Mycobacterium africanum, is the causative agent of the infection tuberculosis. Mycobacterium bovis disease is similar to Mycobacterium tuberculosis disease in that it can manifest itself in a variety of situations, but it is most commonly seen as pulmonary tuberculosis. Early in the disease, there are few or no symptoms, and the disease may be discovered only by chance through a chest roentgenogram. As the disease progresses, there is the development of fever, weight loss, night sweats, chronic and productive cough, and hemoptysis. These symptoms, along with developing chest pain, eventually force the patient to seek medical attention. The organism has a growth rate of 21 - 40 days, is niacin and nitrate-negative, Tween hydrolysis-negative, and urease-positive.
Correct answer:
The patient should undergo serial fetal ultrasounds to monitor for the appearance of signs of hydrops fetalis.

Explanation
Erythema infectiosum, also known as Fifth disease (FD), is a common childhood exanthem caused by parvovirus B19. Spread by respiratory secretions, FD is often preceded by a prodrome of low-grade fever, malaise, pharyngitis, and coryza. FD is readily distinguished from other eruptions by a characteristic "slapped-cheek" rash. This presentation is notable for a bright red macular appearance that favors the malar surfaces, sparing the bridge, orbits, and mouth. Within 1-2 days, another rash develops; it is characterized by symmetric eruptions and blotchy areas that take on a reticular or lacy pattern. The rash may involve other areas of the skin, but most commonly evolves to the extremities and buttocks.

For most children, FD is self-limiting and resolves spontaneously in 1-2 weeks, although the rash may recur after bathing, exercise, and sunlight. In adults, infection may cause an arthritis-like syndrome. In immunocompromised individuals, parvovirus B19 infection may cause anemia. No vaccine is available to prevent parvovirus B19 infection.

For pregnant women, exposure to a child with FD represents a risk to the fetus. Children are most contagious before the rash develops, so exposure has often occurred by the time FD is detected. The pregnant patient should be tested for antibodies. Immunity is protective and lifelong, however only about 50% of the population is immune to parvovirus B19. Although the virus is not highly contagious, risk to those living with an infected individual is high. The pregnant patient who is seronegative should be retested in 2 weeks, whether or not symptoms are present. In about 15-30% of cases, maternal infection will be transmitted to the fetus, and the fetus will develop hydrops fetalis, a condition marked by swelling of the organs - especially liver - pleural and pericardial effusions, and severe anemia. Pregnant women who develop IgM antibodies - a marker of recent infection - should undergo serial ultrasound examinations to monitor for signs of fetal hydrops. It is possible to detect parvovirus in amniotic fluid; however, amniocentesis exclusively for the determination of fetal infection is not routinely performed due to the inherent risk associated with this test. If the fetus becomes infected, intra-uterine transfusions are often the treatment of choice.
Correct answer:
Roseola

Explanation
The description of the presentation best fits that of roseola. Roseola infantum is the sixth of the traditional exanthems of childhood. The condition is an acute benign disease of childhood characterized by a history of a prodromal febrile illness lasting approximately 3 days, followed by defervescence and the appearance of a faint pink maculopapular rash.

Erythema infectiosum, caused by human parvovirus B19, affects children ages 3-12. It exhibits a bright red facial (slapped-cheek) rash. Rubella is more common in older children and is accompanied by other systemic symptoms. If a woman has rubella during the first 3 months of her pregnancy, the virus can induce many different birth defects, some of which are quite severe. Among the defects doctors have seen in congenital rubella are eye defects (cataracts, glaucoma), microphthalmia (small, non-functional eyes), and heart problems (defects of the wall between the two sides of the heart, narrowing of the arteries to the lungs, and an open duct bypassing the lungs). In addition, doctors have seen ear problems (deafness caused by defects in the nerves and sound-sensing organs) and neurologic problems (including intellectual disability).

Rubeola (or measles) usually has a prodromal phase of respiratory symptoms, and it is most common in children ages 5-9.

Scarlet fever due to group A beta-hemolytic Streptococci would also be unusual in this age group, and it is usually accompanied by tonsillopharyngitis.
Correct answer:
Restriction of sport activities

Explanation
The diagnosis is infectious mononucleosis. It is a common disease among young adults (although patients may be of any age), and it may pass unnoticed or cause acute illness that is sometimes followed by lethargy for months. It is caused by the Epstein-Barr virus (EBV), which preferentially infects B-lymphocytes. This follows a proliferation of T cells, the "atypical" mononuclear cells, which are cytotoxic to EBV-infected cells. Most patients exhibit malaise, sweats, sore throat, and anorexia; diarrhea is rare. Splenomegaly occurs in 50% of patients. Hepatomegaly is uncommon. A rash is likely to appear if the patient is given ampicillin. The atypical lymphocytes (of which only a few may be seen) may also be present in many viral infections (especially CMV), toxoplasmosis, drug hypersensitivity, leukemias, lymphomas, and lead intoxication.

It is caused by the Epstein-Barr virus (EBV), which preferentially infects B-lymphocytes. This follows a proliferation of T cells, the "atypical" mononuclear cells, which are cytotoxic to EBV-infected cells. Most patients exhibit malaise, sweats, sore throat, and anorexia; diarrhea is rare. Splenomegaly occurs in 50% of patients. Hepatomegaly is uncommon. A rash is likely to appear if the patient is given ampicillin. The atypical lymphocytes (of which only a few may be seen) may also be present in many viral infections (especially CMV), toxoplasmosis, drug hypersensitivity, leukemias, lymphomas, and lead intoxication.

Treatment includes bed rest and restriction of sport activities to protect the fragile spleen, which is subject to rupture; alcohol should be avoided, and oral prednisolone should be given for severe symptoms or complications. Fatigue is exacerbated by physical exertion.

Digitalis is a cardiac glycoside used to slow the ventricular rate in fast atrial fibrillation. It has a very weak positive inotropic effect and is generally not now used in heart failure. It also has a low therapeutic range, and older people are especially at risk of toxicity.

High doses of steroids can cause suppression of the adrenal cortex, leading to adrenocortical insufficiency. This is a life-threatening event, presenting as shock, salt loss, and hypoglycemia; it is often precipitated by stress, such as infections and malignancies. This is the rationale behind tapering the dose of steroids whenever it is given for a prolonged period for inflammation. High doses of steroids are only given on a therapeutic basis for conditions that lead to adrenocortical insufficiency.

Neither penicillin (a bactericidal antibiotic sensitive to a wide range of mostly gram-positive and certain gram-negative organisms) nor chlorambucil (an immunosuppressive drug used for advanced rheumatoid arthritis and other neoplastic conditions) has any role in the treatment of infectious mononucleosis.



References
Correct answer:
Tetanus and diphtheria toxoids and acellular pertussis vaccine (Tdap)

Explanation
There are pertussis vaccines for children, pre-teens, teens, and adults. The childhood vaccine is DTaP (the pertussis booster vaccine for adolescents and adults is called Tdap). DTaP (full-strength doses of diphtheria (D) and tetanus (T) toxoids and pertussis (P) vaccine) is given to infants and children ages 6 weeks through 6 years. Children should get 5 doses of DTaP, 1 dose at each of the following ages: 2, 4, 6, and 15-18 months, and 4-6 years.

Children aged 7 through 10 years who are not fully immunized against pertussis (including those never vaccinated or with unknown pertussis vaccination status) should receive a single dose of Tdap. Tdap can be administered regardless of the interval since the last tetanus and diphtheria toxoid-containing vaccine.

Herd immunity has an indirect impact on immunity. It reduces the transmission of infectious disease agents from immunized people to others, thereby reducing the impact of infection spread. This patient will provide herd immunity after the immunization.

Influenza vaccine should be given every year, but it will not protect the child from pertussis.

Vaccines containing the whole cell pertussis component (DTP) are no longer recommended for use in the United States. Even though most side effects of the vaccination are moderate, severe problems closely following DPT immunization led to the introduction of acellular pertussis vaccine. The most severe problems with DTP vaccine were symptoms of neurological damage (occurring within the first 7 days following vaccination), thereby raising the risk of permanent brain damage in children.

Preventive antibiotics could be recommended to close contacts, including all household members of a pertussis patient, regardless of age and vaccination status. This might prevent or reduce the chance of getting pertussis. Your patient is not at risk of getting pertussis from close contacts.
Correct answer:
Offer fluconazole, if antibiotics are indicated in the future

Explanation
This patient is presenting with a vaginal yeast infection. It would be most reasonable to offer fluconazole (an antifungal) if antibiotics are indicated in the future. Recent use of antibiotics is a risk factor for development of a vaginal yeast (usually Candida) infection, because the normal protective flora is diminished. Increased duration of antibiotic use is another risk factor for vaginal candidiasis. Of course, appropriate antibiotic prescribing guidelines should be followed. Several other conditions, such as AIDS, diabetes, and pregnancy, can predispose women to frequent vaginal yeast infections. This patient should be evaluated to ensure she does not have any of these other risk factors, as well. If her symptoms did not resolve with treatment, she could be treated for chronic vaginal candidiasis with lengthier regimens of antifungals.

Cranberry juice is often recommended as a preventive method for development of urinary tract infection. It does not have a role in the prevention of yeast vaginitis.

Yogurt consumption has been touted as a natural treatment and preventative measure for yeast vaginitis. The active lactobacillus cultures are thought to help re-colonize "protective" normal vaginal flora. However, the evidence base thus far does not support oral yogurt consumption as having any role in prevention of yeast infections.

While antibiotics appear to be a trigger for this patient's development of yeast vaginitis, it would be inappropriate to withhold antibiotic treatment, especially in the case of her recent group A Streptococcus infection, due to the potentially serious sequellae of the infection, such as post-streptococcal glomerulonephritis and rheumatic fever.

Nitrofurantoin is an antibiotic with good activity for targeting urinary tract organisms. It is useful for both treatment of lower urinary tract infections (UTIs) and prevention of UTIs. It is sometimes given prophylactically post-intercourse for women who develop frequent UTIs. It does not have antifungal properties and would not prevent this woman's yeast infections.
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Correct answer:
Common cold

Explanation
Seasonal upper respiratory infections (URI) that occur during the winter months are often features of the common cold. Young and older individuals may experience a runny nose, sore throat, nasal congestion, headaches, and sneezing. The severity of the URI will vary with different individuals. Levels of partial immunity, induced by prior infections, may alter the severity and duration of the infection; in some instances, they may totally prevent infection. The average individual is infected 2-3 times per year because multiple strains of the infectious agents circulate in the population at any given time.

Common colds are caused by a variety of viruses, such as rhinoviruses, coronaviruses, and adenoviruses. Most URIs are caused by rhinoviruses. Infections spread easily via respiratory droplets produced during sneezing and breathing. More severe respiratory infections are caused by the orthomyxoviruses (influenza viruses). There are over a hundred different viral serotypes capable of causing common colds. Therefore, it is not practical to produce a vaccine. It is also impractical because the infections are generally brief and mild. Older individuals and those who are immunosuppressed are at risk for complications.

Antibiotics, often requested by concerned parents, are ineffective against viral cold infections. Generally, the infections are treated symptomatically in order to ease the discomfort of the patient until the immune system takes over.
Correct answer:
Influenza virus

Explanation
Influenza virus belongs to the family Orthomyxoviridae that contain 2 genera: influenza virus type A and influenza virus type B. There may also be another member of the family, influenza virus type C, which has yet to be officially classified as such. All types, subtypes, and strains have similar structure (80 - 120 nm in diameter, enveloped, and covered with surface projections or spikes). Classic flu symptoms have an abrupt onset after an incubation period of 1 - 2 days. The initial symptoms are systemic; they present as shaking chills, fever, headache, myalgias, malaise, and anorexia. Headache, gastrointestinal symptoms, and myalgias are the symptoms that are most pronounced, and they are related to the fever elevation (which can be between 100 - 104°F). Arthralgia is not uncommon. There is severe eye muscle pain when gazing laterally in some patients. There are usually respiratory symptoms present initially (e.g., dry cough and nasal discharge), which are overshadowed by the systemic symptoms. Early in the illness the patient physically appears toxic, the face appears flushed, the skin is hot and moist, and small, tender cervical lymph nodes can be detected. Transient scattered rhonchi, or localized areas of rales, can occasionally be found. Fevers usually last for 3 - 8 days. Coughs can last longer, and a convalescent period of 1 - 2 weeks or more is needed for full recovery. Influenza illness can lead to complications such as primary influenza viral pneumonia, secondary bacterial pneumonia, cardiac complications, Reye's syndrome, and toxic shock syndrome. Laboratory diagnosis is by viral culture, serological testing, rapid EIA (enzyme immunoassay), and DFA (direct fluorescent antibody) techniques. Antivirals such as amantadine, rimantadine, and ribavirin can be used to lessen the duration and severity of the symptoms. Influenza vaccines are the best method for preventing influenza illness.

Mycoplasma pneumoniae is a short rod (about 10 x 200 nm) that has an organelle responsible for cell membrane attachment at 1 end. It has no cell wall, making it unable to be stained; it is resistant to beta-lactam antibiotics. The culturing process is slow for Mycoplasma pneumoniae (5 - 20 days), as opposed to other bacteria. Mycoplasma pneumoniae produces an atypical pneumonia syndrome. The organism, unlike most viral respiratory infections (which have a 1 - 3 day incubation period), has an incubation period of 2 - 3 weeks. Initially, the infection is upper respiratory in nature. It has an insidious onset, which includes symptoms such as fever, malaise, headache, and cough. The onset is gradual as opposed to influenza infections, and 5 - 10% of patients will progress to tracheobronchitis or pneumonia. The fever is usually 100 - 102° F, sputum Gram stain is positive for inflammatory cells but absent of any predominating organisms, and myalgia and gastrointestinal symptoms are generally rare. The physical appearance of the patient is not indicative of any terrible illness; hence, the origin and use of the term 'walking pneumonia'. Chest examination may produce little or no auscultative or percussive findings. Rales are minimally present. Pleural effusion occurs in 5 - 20% of patients. Chest pain, when present, is usually due to chest strain from coughing. Chest radiographs show patchy areas of lung infiltration. Cold agglutinin testing and complement fixation tests are the most commonly ordered laboratory tests to aid in the diagnosis. Cold agglutinin titers >1:64 are indicative of Mycoplasma pneumoniae infection. Tetracycline, its derivatives, and erythromycin are the drugs of choice in treating Mycoplasma pneumoniae.

Respiratory syncytial virus (RSV) is an enveloped, single negative-strand RNA virus measuring 120 - 300 nm. Repeated infections with RSV are common, and the virus is highly contagious. Patients are generally infants who present with a lower respiratory tract illness, pneumonia, bronchiolitis, tracheobronchitis, or an upper respiratory tract illness; it is often accompanied by fever and otitis media. There may be severe hypoxia present that can be life-threatening. Fever can last 2 - 4 days and cough may be the most frequent and predominant sign. After several days of upper respiratory tract signs and deepening cough, it is not unusual for the onset of dyspnea, increased respiratory rate, and retractions of intercostal muscles. In bronchiolitis, expiration tends to be prolonged; the respiratory rate can reach 80/min. Intercostal retractions are also particularly prominent in bronchiolitis, which emphasizes the inspiratory obstruction of the lower airway exists, as well as the more obvious expiratory obstruction. On auscultation, the patient may have rhonchi, wheezing, and rales that are intermittently present and may fluctuate in intensity. Chest radiographs typically show multiple areas of interstitial infiltration and hyperinflation of the lung. Ribavirin is the drug of choice to treat RSV in infants; it is delivered by aerosol since oral (p.o.) administration can result in hepatic or bone marrow toxicity.

Streptococcus pneumoniae is a Gram-positive staining cocci. It is catalase-negative, alpha-hemolytic on blood agar, appears as diplo-cocci that are 'lancet-shaped', and are bile esculin soluble or sensitive to the copper-containing compound optochin. It is the most common cause of bacterial pneumonia. Streptococcus pneumoniae is most common in the elderly, individuals with a malignancy, immunosuppressed individuals (e.g., HIV, drug use, chronic alcoholism, and organ transplant recipients), diabetics, asplenic individuals, and those with chronic liver, heart, and/or kidney disease. Penicillins and cephalosporins are the drugs of choice; however, resistant isolate-possessing penicillin-binding proteins (PBPs) have increased in frequency.

Staphylococcus aureus pneumonia can result either from aspiration or hematogenous spread. The organism is a Gram-positive coccus, catalase-positive, coagulase-positive, predominantly beta-hemolytic on blood agar, and appears in characteristic grape clusters on Gram stain. It is common for Staphylococcus aureus pneumonia to occur in a patient that has been stricken by influenza a few days prior. This is especially true in the debilitated, immunocompromised, and the elderly. X-rays can show a continuous spectrum of findings; however, there are indicators that can point to a Staphylococcus aureus pneumonia (e.g., rapid cavitation of the lungs, poor response to therapy aimed at treating pneumococcal pneumonia, and the development of pleural empyema). A semisynthetic penicillin or vancomycin is the treatment of choice. Cases of empyema may require surgery, treatment by the IV route, and drainage of the empyema by the insertion of a chest tube.
Correct answer:
Chlamydia trachomatis

Explanation
Chlamydia trachomatis is seen in infants 3-16 weeks old. They are usually sick for several weeks. On exam, the infant is nontoxic, afebrile, usually tachypneic, and has a prominent cough. Conjunctivitis is seen in about 50% of cases. The chest film demonstrates diffuse interstitial patches.

Human parvovirus (or parvovirus B19) causes erythema infectiosum. The disease typically affects children older than the patient. It presents as a low-grade fever, a facial rash with a slapped-cheek appearance, and a lacy, reticular-like maculopapular rash on the trunk and extremities. Gastrointestinal upset, coryza, and myalgia are associated symptoms.

Parainfluenza virus presents as upper respiratory infections of several days duration. Symptoms include a hoarse, croupy, cough and inspiratory stridor. The child is restless with retractions evident in severe infections. It usually resolves in 48-72 hours, but should it progress longer, it can manifest as laryngeal obstruction. Steeple sign is seen on a lateral X-ray of the neck, with glottic and subglottic narrowing.

Respiratory syncytial virus begins with pharyngitis and rhinorrhea, which are followed by 1-3 days of coughing and wheezing. In addition to wheezing, diffuse rhonchi and fine rales can be auscultated. The chest film is normal. Chlamydial infections may be differentiated from RSV by conjunctivitis and a subacute onset.

Staphylococcal pneumonia has a sudden onset; the child appears toxic and febrile, with an expiratory wheeze at onset that simulates bronchiolitis. There may also be signs of abdominal distress, tachypnea, dyspnea, and localized or diffuse bronchopneumonia. There is prominent leukocytosis.
Correct answer:
Lyme disease

Explanation
The pathogenic agent of Lyme disease is a spirochete bacterium, Borrelia burgdorferi. It is passed to humans by the bite of the hard-shelled ticks of the Ixodes genus. Several days to a month after infection, a rash develops at the sight of the bite. Known as erythema chronicum migrans, this erythematous lesion often expands over the course of several weeks and typically appears with a red flat border and central area of clearing. The ECM lesion gradually fades over several weeks, but new transient lesions may subsequently appear in various areas.

Early signs and symptoms include general malaise and severe fatigue with fevers and chills. Headache, musculoskeletal pains, myalgias, and lymphadenopathy are common. If untreated, later phases may include neurological symptoms, cardiac dysfunction, and an asymmetrical pattern of arthralgias and arthritis that may resemble early rheumatoid arthritis. Confirmatory diagnosis relies on serum antibody assays using ELISA or immunofluorescence. Antibiotic treatment is usually effective.

Group A streptococcal bacteria infection initiating in the upper respiratory tract, causes acute rheumatic fever, generally in young children. Inflammatory changes may damage the heart, joints, blood vessels, and subcutaneous tissues. Clinical course usually begins with an episode of acute pharyngitis. After a few weeks, it is followed by fever and migratory polyarthritis. Typically, this involves painful swelling of the joint, which subsides after several days with no residual disability. Skin lesions may develop as subcutaneous nodules or a rash called erythema marginatum, which usually has a bathing-suit distribution. The rash has prominent erythematous margins and may expand, but transient lesions developing in other areas are not expected. Myocarditis often develops. It may involve friction rubs, arrhythmias, cardiac dilation, or valvular damage. Recurrent episodes may appear, and they often follow the same pattern as the initial episode. Culture or serological testing can be used for confirmation. Treatment with antibiotics is usually successful.

Alcoholic cirrhosis of the liver typically leads to clinical symptoms of general malaise, weakness, weight loss, and loss of appetite. Later, jaundice, ascites, and peripheral edema develop. The general syndrome usually takes decades of abuse to develop, and it progresses slowly with deteriorating hepatic function and the development of secondary problems associated with portal hypertension.

Malaria is caused by the protozoan parasite Plasmodium, and it is transmitted by the Anopheles mosquito. Several different types are possible, depending on the particular infecting specie. General symptoms are flu-like and include headache, nausea and vomiting, myalgia, photophobia, and anorexia. The chills, fevers, and rigors reappear periodically as the cycle of infection, replication, and RBC lysis progresses (36, 48, or 72 hours is typical, depending on the species involved). Diagnosis is by microscopic examination of blood smears for the presence of the parasite. Serological tests are also available. Treatment is with chloroquine or parenteral quinine and primaquine.

Polymyalgia rheumatica is characterized by pain and stiffness in the proximal muscle groups of the neck, shoulders and pelvis, usually symmetrically. Temporal arteritis with associated headache symptoms is common. Fever, malaise, anorexia, and weight loss may be present, as well as swelling of 1 or 2 joints. There is no associated rash expected. The erythrocyte sedimentation rate will be elevated, but there will be negative rheumatoid factor presence. Treatment with corticosteroids should produce a quick, favorable response.