41 terms

Disease Detectives

An aggregation of cases over a particular period closely grouped in time and space, regardless of whether the number is more than the expected number
More cases of a particular disease than expected in a given area or among a specialized group of people over a particular period of time
Large numbers of people over a wide geographical area are affected
An epidemic occurring over several countries or continents and affecting a large proportion of the population.
The systematic and ongoing collection, analysis, interpretation, and dissemination of health data. The purpose of public health surveillance is to gain knowledge of the patterns of disease, injury, and other health problems in a community so that we can work towards their prevention and control.
A serious, potentially life-threatening infectious disease that is usually transmitted to humans by the bites of rodent fleas. It was one of the scourges of our early history. There are three major forms of the disease: bubonic, septicemic, and pneumonic.
An animal that transmits disease.
A physical object that serves to transmit an infectious agent from person to person.
The probability that an individual will be affected by, or die from, an illness or injury within a stated time or age span.
An infectious disease that is transmissible from animals to humans.
incubation period
Time in between when a person somes into contact with a pathogen and when they first show symptoms or signs of disease.
endemic disease
Present at a continuous level throughout a population/geographic area; constant presence of an agent/health condition within a given geographic area/population; refers to the usual prevalence of an agent/condition.
Environmental Causes of Health Problems
Smoking, air pollution
Flooding and drought
Extreme heat, UV exposure
Pesticides, chemical spills, lead contamination
Water pollutants, heavy metals
Ventilation pollutants
Noise induced hearing loss
Waste and toxic substance
Food contamination
Other pathogenic agents as prions
Foods most associated with food borne illness
Raw meat and poultry
Raw eggs
Unpasteurized milk
Raw shellfish
Raw fruits and vegetables
Unpasteurized fruit juice
food processing concerns
Foods that mingle the products of several individual animals
A pathogen in one animal can contaminate may contaminate a whole batch of food mingling the products of several animals as bulk raw milk, pooled raw eggs or ground beef
A single hamburger may contain meat from hundreds of animals
A glass of raw milk may contain milk from hundreds of cows.
A broiler chicken carcass can be exposed to the drippings and juices of many thousands of other birds that went through the same cold water tank after slaughter.
Washing fruits and vegetables can decrease but not eliminate contamination
Processing food under less than sanitary conditions can cause outbreaks
Raw sprouts that are eaten without cooking may contain growing microbes
Storage and transport methods for food
reducing the risk of food borne illnesses
Cook meat, poultry, and eggs thoroughly
Separate - don't cross-contaminate one food with another
Chill - refrigerate leftovers promptly
Clean - wash produce
Report - suspected food borne illnesses to the local health department
centers for disease control (and prevention)
world health organization
odds ratio
used in case-control study, ad/bc
relative risk
used in cohort study, (a/(a+b))/(c/(c+d))
attack rate
the rate that a group experienced an outcome or illness equal to the number sick divided by the total in that group.
epi curve
a histogram that shows the course of an outbreak by plotting the number of cases of a condition according to the time of onset.
continuous common source
occur when the exposure to the source is prolonged over an extended period of time and may occur over more than one incubation period. The down slope of the curve may be very sharp if the common source is removed or gradual if the outbreak is allowed to exhaust itself
Propagated (progressive source)
occur when a case of disease serves later as a source of infection for subsequent cases and those subsequent cases, in turn, serve as sources for later cases. The shape of this curve usually contains a series of successively larger peaks, reflective of the increasing number of cases caused by person-to-person contact, until the pool of those susceptible is exhausted or control measures are implemented.
chain of infection
Agent leaves reservoir through portal of exit, and is conveyed by some mode of transmission, and enters the appropriate portal of entry to infect a susceptible host.
A microbial organism with the ability to cause disease.
A place where agents can thrive and reproduce.
portal of exit
A place of exit providing a way for an agent to leave the reservoir; the route a pathogen takes out of an infected host. Portals of exit tend to be fairly well defined. What serve as portals of exit are often not terribly surprising, at least, once something is known of how and where a pathogen replicates and enters new hosts. Respiratory infections tend to utilize the mouth and nose as portals of exit. Gastrointestinal diseases tend to exit in feces or saliva, depending on the site of replication. Sexually transmitted diseases tend to have portals of exit at the urethra or genital region. Blood-bourne diseases tend to exit via arthropods, needles, bleeding, or hyperdermic syringes. A more general portal of exit occurs when an infected animal is butchered or an infected person undergoes surgery. The three most common portals of exit are the skin, gastrointestinal tract, and respiratory tract.
mode of transmission
Method of transfer by which the organism moves or is carried from one place to another; the transfer of disease-causing microrganisms from one environment to another, particularly from an external environment to a susceptible individual. There are three general categories of transmission: contact, vehicle, and vector.
portal of entry
An opening allowing the microorganism to enter the host; the route a pathogen takes to enter a host. Just as with the portals of exit, many pathogents have preferred portals of entry. Many pathogens are not able to cause disease if their usual portal of entry is artificially bypassed. The most common portal of entry is the mucous membrane of the respiratory tract.
Susceptible Host
A person who cannot resist a microorganism invading the body, multiplying, and resulting in infection.
Characteristics of Agents
Infectivity - capacity to cause infection in a susceptible host
Pathogenicity - capacity to cause disease in a host
Virulence - severity of disease that the agent causes to host
direct contact
occurs through touching, kissing, and/or sexual intercourse.
indirect contact
occurs from a reservoir via inanimate objects called fomites. Fomites are basically almost anything an infected individual or reservoir can touch, upon which can be left a resdiue of contagious pathogent. Exceptions include the various inanimates ferred to as vehicles: food, air, and liquids. Typically, it is more difficult to avoid indirect contact transmission than it is to avoid direct contact transmission. A certain degree of organismal durability may be necessary to survive passage on a fomite. The best way to prevent indirect contact transmission is by avoiding contact with fomites, avoiding contact of hands with mucous membranes, especially when handling or potentially handling fomites, the use of barriers when handling fomites, and disinfecting fomites before handling.
Droplet transmission
consequence of being coughed, sneezed, or spit on. To be considered droplet transmission, mucous droplets must still be traveling with the velocity imparted on it leaving the mouth. As a rule of thumb, this is up to one meter after exiting the mouth. Any further and this is considered airborne transmission. Given interaction within one meter of people is certainly more difficult to avoid droplet transmission than it is to avoid either direct or indirect transmission. Not surprisingly, it is especialy respiratory diseases that are transmitted by droplets.
airborne transmission
occurs via droplets (typically mucous droplets) where droplets are liquids that remain airborne whether as aerosols (very small droplets) or associated with dust particles. An example is within airliners where economizing measures reduces the turnover of cabin air and consequently increases air recycling. Organisms which can find their way into the air and remain viable thus have repeated opportunities to infect passengers. It requires greater organismal durability that droplet transmission simply because of the length of time the microorganism is exposed to the air, before infecting a new host, is longer. Increased durability is to the effects of desiccation, exposure to sunlight, etc. This is why breathing does not typically result in the acquisition of disease.
Food-bourne Transmission
any number of pathogens are found in food and not killed during processing may be transmitted via food product. Salmonella especially tends to be part of the normal flora of chickens and consequently associated with chicken products.
water-bourne transmission
fecal contaminated water. Generally, this is via sewage contaminated water supplies. It is especially gastrointestinal pathogens that are present in feces and therefore which rely on this type of transmission.
portals of entry to the nervous system
the brain is typically fairly resistant to bacterial infection. There are four common portals of entry to the nervous system. For an organism to take advantage of these routes, they must display increasingly specialized adaptations as read from first to last: parenteral, via the blood, via the lymphatic systems, and up the peripheral nerve axons. Ordering of blood and lymphatic system was arbitrary and not intended ot imply that one serves as a significantly more difficult portal to take advantage of than the other.
disease prevention
Cook meat, poultry, and eggs thoroughly.
Don't cross-contaminate one food with another.
Chill and refrigerate leftovers promptly.
Clean and wash all produce.
Report suspected food-borne illnesses to the local health department.
ten steps to investigating an outbreak
Prepare for Field Work
Establish the Existence of an Outbreak - Consider Severity, Potential for Spread, Public Concern, and Availability of Resources
Verify the Diagnosis
Define and Identify Cases - Case Definition and Line Listing
Describe and Orient the Data in Terms of Person, Place, and Time - Descriptive Epidemiology
Develop Hypotheses (Agent/Host/Environment Triad) = Chain of Transmission
Evaluate Hypotheses - Analytical Studies (MUST Have a Control Group)
Refine Hypotheses and Carry Out Additional Studies
Implement Control and Prevention Measures (ASAP!)
Communicate Findings