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Dr. Eccles Module 3 Chapter 14: Principles of Disease and Epidemiology And Mastering homework, quizes, and tests


Organisms that cause disease. They have special invasive properties or produce toxins.

Normal Flora

normal flora of an organism are permanent residents that do not cause infection. An example of these would be the organisms that normally live on your skin. They actually keep harmful organisms from being able to establish residence


The cause of a disease


The invasion or colonization of the body by a pathogenic microorganism


When and infection results in any change from a state of health. When all or part of the body is incapable of performing its normal functions

Transient Microbiota

microorganisms may be present for days, weeks or months and then disappear


Refers to the relationship between normal flora and the host.


One species is harmed and it is difficult to see how other is benefited.
Example: S. aureus and Penicillium mold. Mold releases Penicillin to kill S. aureus. Benefit to mold hard to see.


One organism benefits and the other is not harmed.
Ex: Streptococcus viridans lives in your mouth. It does no harm but living here is beneficial to the bacterium because it grows well in this area.


Two species live together and both benefit.
Ex. The large intestine contains E. coli that synthesizes vitamin K and B. They are then absorbed in by the blood stream for cells. In exchange, the intestine provides nutrients for E. coli's survival


The organism lives in the host. Parasite benefits but host may be harmed. A successful parasite will not kill its host.
Ex: Measles

Opportunistic Pathogens

Ordinarily don't cause disease in their normal habitat but may do so in a abnormal environment. Ex. Cut

Koch's Postulates

This series of steps is used by microbiologists to determine the etiology or causative agent of a disease.
1. The same pathogen must be present in every case of the disease
2. The pathogen must be isolated from the diseased host and grown in pure culture
3. The pathogen from the pure culture must cause the disease when it is inoculated
4. The pathogens must be isolated from the inoculated animal and must be shown to be

Koch's Postulates Procedure

1. Microorganisms are isolated from a diseased or dead animal
2. Microorganisms are grown in a culture and identified
3. Microorganisms are injected into a healthy animal
4. Disease is reproduced in a laboratory animal
5. Microorganisms are isolated from this animal and grown in a culture then identified.


A change in body function that is felt by a patient as a result of disease. Ex. Pain


A change in a body that can be measured or observed as a result of disease. Ex. Swelling, fever


A specific group of signs and symptoms that accompany a disease.

Communicable Disease

Any disease that spreads from one host to another directly or indirectly. Ex. Chickenpox, measles, genital herpes, typhoid fever

Contagious Diseases

Diseases that are spread easily spread from one person to another (type of communicable disease)

Noncommunicable Disease

A disease not spread from one person to another. Ex. Tetanus, Clostridium tetani produces disease only when it is introduced into the body via wounds

Incidence of a Disease

The proportion of the population affected by a disease at a specific point in time. Indicator of spread.

Prevalence of a Disease

The number of people in a population who develop a disease at a specific time, regardless of when it first appeared. Both old and new cases. Indicator of how seriously and how long a disease affects a population.

Sporadic Disease

Occurs only occasionally. Ex. Typhoid

Endemic Disease

Constantly present in a population. Ex. common cold

Epidemic Disease

Many people in a given area acquiring a a certain disease in a relatively short period of time. Ex. Influenza

Pandemic Disease

An epidemic disease that occurs worldwide. Ex. AIDS

Acute disease

Develops quickly and lasts a short time. Ex: Influenza

Chronic disease

Develops slowly and persists. Ex: Leprosy

Latent Disease

The causative remains inactive for a long time and reappears. Ex: Varicella zoster virus causes shingles which is a reactivated chicken pox infection.

Subacute Disease

A disease the is intermediate between acute and chronic. Ex. Sclerosing panencephalitis, rare brain disease

Local Infection

Limited to a small area. Ex: Boil

Systemic (generalized) Infection

spreads through body via blood or lymphatic system. Ex: Measles


A toxic inflammatory condition arising from the spread of microbes, especially bacteria, from a focus infection.
Ex. Septicemia, also called blood poisoning is a systemic infection arising from the multiplication of pathogens in the blood.

A Reservoir of Infection

A continuous source of infectious agents. It may be living or nonliving.


Human resevoirs-people with disease Ex. aiDS, diphtheria, typhoid fever, hepatitis, gonorrhea, amebic dysentery, and streptococcal infections


Animal reservoirs- infect wild or domestic animals and can be transferred to humans.

Transmission of Disease

1. Direct Contact
2. Indirect contact - fomites (inanimate objects)
3. Droplet Transmission
4. Vehicle transmission
5. Airbourne
6. Arthropod vectors

Direct Contact

Person to person-touching, kissing, banging chicks/dudes

Indirect Contact

Transfering via nonliving host-tissues, towles, money, drinking cups

Droplet Transmission

Mucus droplets - coughing, sneezing, laughing

Vehicle Transmission

Transmission of a disease by a medium such as food, water, or air-blood, drugs

Waterborne Transmission

A type of vehicle transmission-poorly treated sweage

Foodborne Transmission

A type of vehicle transmission- under cooked food, poorly refrigerated food

Airborne Transmission

A type of vehicle transmission-fine droplets from sneezing


Animals that carry pathogens from one host to another-insects

Mechanical Transmissions

The passive transport of the pathogens n the insect's feet

Patterns of Disease

1. Need reservoir
2. Carried to host
3. Invades and injure host

Occurrence ultimately depends upon:

Resistance of host to pathogens.

Predisposing factors

Make one more susceptible or resistant. For example, the genetic disease sickle cell anemia gives resistance to malaria.

The development of a disease follows a definite pattern:

-incubation period
-prodromal period
-period of illness
>ends in death or life<
-period of decline
>can get a secondary infection<
-period of convalescence


Involves the study of factors influencing host-parasite relations.

Epidemiologist Monitors:

Morbidity and Mortality


The number of people infected with a given organism in a given time period.


The number of deaths in a given population in a given time period.

Nosocomial infections

Are acquired as a result of a hospital stay. Patients on antimicrobial therapy or immunosuppressants are most susceptible. Five to fifteen percent of all hospital patients acquire them.

Interaction of three factors leads to nosocomial infections:

(1.)Presence of microorganisms in the hospital environment.
(2.) A weakened or compromised host.
(3.) A chain of transmission in the hospital. One of the three is usually not enough to pose a significant risk.

Emerging Infectious Diseases

Emerging diseases are diseases that are new, increasing in incidence, or showing a potential to increase in the near future.
Contributing factors include:
-Genetic recombination
-Evolution of new strains
-Inappropriate use of antibiotics and pesticides.

Emerging diseases may result from

-Changes in weather patterns: Hantavirus
-Modern Transportation: West Nile virus
-Ecological disaster, war, and expanding human settlement: Coccidioidomycosis
-Animal control measures: Lyme disease
-Public Health failure: Diphtheria

All members of the seven families for whom Mary Mallon prepared meals developed typhoid fever. Mary did not get sick. This is an example of __________.

a carrier

What is the difference between normal and transient microbiota?

Normal microbiota are permanently present.

Koch's postulates are a set of guidelines to follow if you want to __________.

prove that a specific infectious disease is caused by a specific microorganism

A disease that is constantly present in a population is called a(n) __________.

endemic disease

Which type of nosocomial infection is the most common?

urinary tract infection

On October 29, Barbara participated in a study group for her microbiology class. On November 1, Barbara had a "scratchy throat" when she swallowed. On November 2, Barbara had a headache, runny nose, and watery eyes. She was fully recovered on November 7. During which time was Barbara in the prodromal period?

November 1

John Snow analyzed information about cholera victims, including where the victims lived and where they got water. This is an example of __________.

descriptive epidemiology

Florence Nightingale compared disease rates and other statistics for soldiers versus civilian populations. This is an example of __________.

analytical epidemiology

Ehrlichiosis is transmitted by ticks. This is an example of __________.

vector transmission

Which of the following body sites typically does NOT have normal microbiota?

The kidney

he fungus Coccidioides immitis is found in the soil. Humans contract coccidioidomycosis by inhaling fungal spores. Which of these descriptions applies to the role of soil in transmission of coccidioidomycosis?

Soil is the reservoir.

An infection that does NOT cause any signs of disease is a(n) __________.

subclinical infection

Alfalfa sprouts were responsible for transmitting Salmonella to 32 people in four states. This is an example of __________.

vehicle transmission

Two patients developed endophthalmitis within 24 hours after corneal transplant surgery. Streptococcus pneumoniae was isolated from conjunctival swabs of the affected eyes of both patients and from the supply of packing that was used to cover the eyes after surgery. This is an example of __________.

a nosocomial infection

On October 29, Barbara participated in a study group for her microbiology class; one of her classmates had a cold. On November 1, Barbara had a "scratchy throat" when she swallowed. On November 2, Barbara had a headache, runny nose, and watery eyes. She was fully recovered on November 7. Identify the incubation period for this infection

October 29 to November 1


The presence of bacteria in the blood


The presence of toxins in the blood


The presence of viruses in the blood

Primary Infection

An acute infection that causes the initial ilness

Secondary Infection

One that is caused by an opportunistic pathogen after the primary infection has weakened the body's defenses. Seconadary infection of the skin and respiratory tract sometimes more dangerous than primary infection.
EX. Pneumocystis pneumonia as consequence of AIDS
EX. Streptococcal bronchopneumonia following influenza

Subclinical (inapparent) Infection

One that does not cause any noticeable illness

Predisposing factor

Makes the body more susceptible to a disease and may alter the course of the disease.
ex. Gender, genetic background, climate and weather, inadequate nutrition, fatigue, age, environment, habits, lifestyle, occupation, preexisting illness, chemotherapy, and emotional disturbances.

Incubation Period

First stage in the development of a disease. The interval between the initial infection and the first appearance of any signs or symptoms. an be the same or variable depending on the specific microorganism.

Prodromal Period

Second stage in the development of a disease. A relatively short period that follows the period of incubation in some diseases. Early mild symptoms

Period of Illness

Third stage in the development of a disease. When the disease is most severe. Overt signs and symptoms of disease. Dies in this stage if disease is not successfully overcome.

Period of Decline

Third stage in the development of a disease. The signs and symptoms subside. Lasts less than 24 hours to a few days. Patient is vulnerableto secondary infections at this time.

Period of Convalescense

Fourth stage in the development of a disease. Regains strength and returns to normal state. Can spread infection in all four stages.

Health Care-associated infection (HAI)

CDC estimates 5-15% of all hospital patients acquire some type of nosocomial infection. Result from
1. Microorganisms in the hospital environment
2. weakened status of the host (nosocomial infections do not cause disease in healthy people)
3. chain of transmission in the hospital
Some microorganisms in the hospital become resistant to antimicrobial drugs

Compromised Host

A host whose resistance to infection is impaired by disease, therapy, or burns. Two principal conditions can compromise the host: broken skin or mucouse membranes, and a suppressed immune system.
Ex. urns, surgical wounds, injections, ventilators, intravenous therapy, urinary catheters

T cells

A type of White Blood Cell (T lymphocytes) that provide resistance to disease by killing pathogens directly, mobilizing phagocytes and other lymphocytes, and secretin chemicals that kill pathogens

B cells

White blood cells (B lymphocytes) that develop into antibody-producing cells, also protect against infection

Chain of transmission

The principal routs of transmission of nosocomial infections are
1. direct contact transmission hospital staff to patient and from patient to patient
2. indirect contact transmission through fomites and the hospital's ventilation system (humidifiers and respirators also give way to airborne transmission)

Control of Nosocomial Infections

CDC says hanwashing is the single most important means of preventing the spread of infection

emerging Infectious diseases (EIDs)

Ones that are new or changing, showing an increase in incidence in the recent past, or a potential to increase in the near future.

e. coli O157:H7 and avian influenza (H5N1)

These new strains may result from genetic recombination between organisms

widespread and unwarranted use of antibiotics and pesticides

encourages the growth of more resistant populations of microbes and the insects and ticks that carry them

global warming and changes in weather patterns

may increase the distribution and survival of reservoirs and vectors resulting in the introduction and dissemination of diseases such as malaria and hantavirus pulmonary syndrome

streptococcus pyogenes

Causes Puerperal sepsis (chilbirth fever), a nosocomial infection that starts in the uterus as a result of childbirth or abortion

Descriptive epidemiology

entails the collecting all the data that describe the occurrence of the disease under study. Includes information about the infected individuals and the place and period in which the disease occurred. Retrospective, looking back and backtracking to find the cuase and source of the disease.

Analytical epidemiology

Analyzes a particular disease to determine its probable cause. two ways:
1. case control method-studying two populations: one that has contracted the disease and one that has not
2. Cohort method- studying two populations: one that has had contact the disease and another that has not.

Experimental Epidemiology

Begins with a hypothesis about a particular disease. ex. effectiveness of a drug. One group of people with a condition are split: one gets drug, other gets a placebo

case reporting

a procedure that requires health care workers to report specific diseases to local, state, and national health officials

Morbidity rate

the rate of people affected by a disease in a given period of time in relation to the total population

Mortality rate

the number of deaths resulting from a disease in a population in a given period of time in relation to the total population

Notifiable infectious diseases

diseases for which physicians are required by law to report cases to the us public Health service. 2011 total was 62 infectious diseases

microbial Antagagonism or competitive exclusion

the normal microbiota can benefit the host by preventing the overgrowth of harmful microorganisms. competition among microbes

Germ-free (gnotobiotic) animals often are more susceptible to infections and serious disease than are animals with a typical complement of normal microbiota. Based on this observation, which of the following would be an appropriate conclusion?

Normal microbiota stimulate the development of the immune system.

In a healthy human, resident microorganisms would be found in all of these areas except ________.


Health care professionals who fail to use aseptic techniques can cause ________.

nosocomial infections

In the human intestinal tract, E. coli produces vitamins beneficial to the host and can inhibit pathogen growth. In turn, the bacterium is supplied with nutrients and an environment for growth. This symbiotic relationship between E. coli and its host is an example of ________.


Which of the following is not an example of microbial antagonism (also known as competitive exclusion)?

microbes producing vitamins and growth factors that can be utilized by the host

An infection transmitted by a hypodermic needle is transmitted by ________

indirect contact

Which of the following is not necessary to satisfy Koch's postulates?

The organism must cause disease through toxin production.

Following coronary artery bypass surgery, seven patients develop Rhodococcus bronchialis infections. Cultures of the operating rooms, Nurse A, and Nurse B are taken. R. bronchialis grows from the hand and nasal swabs of Nurse A. The patients' infections are an example of a/an ________.

nosocomial infection

Women who have a healthy population of Lactobacillus spp. as part of the normal vaginal microbiota are less likely to get yeast infections. Which of the following terms is used to explain this observation?

competitive exclusion

The occurrence of streptococcal bronchopneumonia in an individual recovering from influenza is an example of a/an ________.

secondary infection

Infections in which the pathogen is distributed throughout the body are referred to as "generalized infections" or ________.

systemic infections

In a patient with bacteremia, you would expect to find ________.

bacteria in the blood

Which of these diseases does not have a human reservoir?


Which of these events is an example of contact transmission?

A person drinks from a cup used by another individual

Which of these disease stages is most likely to be altered in length if the number of infecting organisms at the start of the infection is very high?

incubation period

Any of these events may occur in diseases transmitted by vectors except ________.

In biological transmission, the vector multiplies in the human host

Which of the following is the third stage of a disease?

period of illness

The morbidity rate is best defined as ________.

the number of individuals, relative to the population, affected by a particular disease in a period of time

Ingesting lactic acid bacteria to prevent colonization by intestinal pathogens such as Salmonella enterica during antibiotic therapy is an example of ________.


An example of descriptive epidemiology is ________.

John Snow's study of the London cholera outbreak in 1848-1849

Biological transmission

an active process. the arthropod bites and infected person or animal and ingests some of the infected blood. the pathogens then reproduce in the vector.

Most microorganisms are pathogenic and harmful to the human body


A host can harbor a pathogen without developing a disease


Disease symptoms are readily measured by health care professionals


Tetanus, which humans acquire from wounds that become infected with the soil microbe Clostridium tetani, is considered noncommunicable


Transmission of Plasmodium spp. (malaria) through a mosquito bite is an example of vehicle transmission.


Water can serve as a human reservoir of Vibrio cholerae


In biological transmission, pathogens reproduce in the vector


A nosocomial infection is one that develops as a result of a stay in a health care facility.


Depending on the disease, individuals can be contagious during the incubation and prodromal periods as well as the periods of illness, decline, and convalescence.


The common cold is considered to be endemic in the United States.


Microorganisms that typically colonize a host without causing disease are referred to as the __________.

normal microbiota

During the __________, a person recovers from a disease and the body returns to its pre-disease state

period of convalescence

__________ pathogens are those that do not cause disease in their normal habitat but may do so in a different environment


The protection from infection received when individuals susceptible to a particular disease live in a population where many individuals are immune is referred to as __________.

herd immunity

Live cultures of bacteria that can be ingested and are intended to produce a beneficial effect in humans are known as __________.


An infection transmitted by a hypodermic needle is transmitted by ________.

indirect contact

The fungus Coccidioides immitis is found in the soil. Humans contract coccidioidomycosis by inhaling fungal spores. Which of these terms applies to the role of soil in transmission of coccidioidomycosis?

Soil is the reservoir.

Which one of these diseases is noncommunicable?

botulism is not spread from person to person, and is thus considered a noncommunicable disease.

Consider these five infectious diseases: Ebola hemorrhagic fever avian influenza SARS West Nile encephalitis mad cow disease Which of these features is shared by this group of diseases?

These diseases are considered to be emerging infectious diseases.

Transmission of Plasmodium spp. (malaria) through a mosquito bite is an example of vehicle transmission.


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