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Definitions of terms from Disease Detectives


the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems


relationship between the number of cases of disease and the size of the population


occurrence of health-related events by time, place, and person


causes and other factors that influence the occurrence of disease and other health-related events

Father of Epidemiology

John Snow

Public Health Surveillance

ongoing, systematic collection, analysis, interpretation, and dissemination of health data to help guide public health decision making and action


ability of a program to produce the intended results in the field


the ability to produce results under the ideal conditions


ability of the program to produce the intended results minimum expenditure of time and resources

Case Definition

a set of standard criteria used for classifying whether a person has a particular disease, syndrome, or other health condition

Descriptive Epidemiology

Type of epidemiology which only covers time place and time to describe an outbreak rather than case definition, person, place, time, and causes/risk factors/modes of transmission

Analytic Epidemiology

The type of epidemiology turned to to test hypotheses formed with information acquired through descriptive epidemiology

Experimental studies

Form of analytic epidemiology which tests hypotheses in a very controlled environment

Observational studies

Type of analytic study in which the epidemiologist simply observes the exposure and disease status of each participant. (Cohort, case-control, and cross-sectional)

Cohort Study

Epidemiologist tracks whether or not the participant is exposed and then tracks them to see if they develop the disease. It is the most reliable form of analytic study, but most expensive and time-consuming.

prospective study

A study which monitors exposure first, then looks forward to see if disease is developed.

retrospective study

starts with people already diseased, then traces back to see if they had been exposed

Case-control study

enroll people with disease and use people without the disease. they then compare previous exposures between the two groups

cross-sectional study

the least expensive and least effective analytic study

Epidemiological triad

agent host environment


A microbe which causes disease


the human who develops the disease


extrinsic factors that affect the agent and the opportunity for exposure

Incubation period

the stage of subclinical disease extending from the time of exposure to onset of disease symptoms for infectious diseases

Latency period

the stage of subclinical disease extending from the time of exposure to onset of disease symptoms for chronic disease

Spectrum of disease

the disease process resulting in illness which is mild, severe, or fatal and eventually ends in recovery, disability, or death


the proportion of exposed persons who become infected


the proportion of infected individuals who develop clinically apparent disease


the proportion of clinically apparent cases that are severe or fatal


persons who are infectious but have subclinical disease


the habitat in which the agent normally lives, grows, and multiplies

portal of exit

the path by which a pathogen leaves its host

mode of transmission

the way through which an agent is transmitted to its host

portal of entry

the manner in which the pathogen enters a susceptible host

direct transmission

an infectious agent is transferred from a reservoir

direct contact

skin to skin contact

droplet spread

spray with relatively large, short-range aerosols produced by sneezing, coughing, or even talking

indirect transmission

the transfer of an infectious agent from a reservoir to a host by suspended air particles, inanimate objects, or vectors


transmission occurs when infectious agents are carried by dust or droplet nuclei suspended in air

herd immunity

suggests that if a high enough proportion of individuals in a population are resistant to an agent, then those few who are susceptible will be protected by the resistant majority since the pathogen will be unlikely to "find those few susceptible individuals

endemic level

the amount of a particular disease that is usually present in the community


a disease that occurs infrequently and irregularly


the constant presence and or usual prevalence of a disease or infectious agent in a population within a geographic area

common source outbreak

an outbreak in which a group of persons are all exposed to an infectious agent or toxin from the same source

point source outbreak

if the group is exposed over a relatively brief period, so everyone who becomes ill does so in on incubation period, then the common source outbreak is further classified as a point source outbreak

continuous common-source outbreak

common source outbreaks in which patients have been exposed over a period of days, weeks, or longer

intermittent common-source outbreak


propagated outbreak

results from transmission from one person to another

mixed epidemics

an epidemic with features of both a common-source outbreak and a propagated outbreak


the relative magnitude of two quantities or a comparison of any two values


the comparison of a part to the whole


a measure of the frequency with which an event occurs in a defined population over a specified period of time

incidence rate

conveys a sense of speed with which disease occurs in a population, and seems to imply that this pattern has occurred and will continue to occur for the foreseeable future

attack rate

the proportion of the population that develops illness during an outbreak

case fatality rate

the proportion of persons with the disease who die from it

prevalence rate

the proportion of the population that has a health condition at a point in time

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