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Basic Epidemiology Terms

Basic epidemiology terms and definitions.
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Agent
Entity necessary to cause disease in a susceptible host
Pathogenicity
The capacity to cause infection in a susceptible host
Virulence
The severity of disease that the agent causes in the host
Host
The organism that is susceptible to the effect of the agent
Environment
The conditions or influences that are not a part of the agent or host, but influence their interactions
Source for the Agent
Place where the agent originates, lives, grows, and multiples
Portal of Exit
Pathway by which the agent can leave the source
Mode of Transmission
The means of carrying the agent to the host
Direct Transmission
Transmission through contact
Indirect Transmission
Airborne, Vector borne, or Vehicle borne transmission
Portal of Entry
Pathway into the host that gives the agent access to tissue where it can multiply or act
Epidemic
Occurrence of more cases of disease than would normally be expected in a specific place or group of people over a given period of time
Outbreak
Another term for "Epidemic"
Endemic
High background rate of disease
Pandemic
Very widespread, often global, disease
Case Definition
Set of standard criteria for deciding whether or not a person has a certain disease
Absolute Risk
The observed or calculated probability of an event under study
Association
Statistical dependence between two or more events, characteristics, or other variables
Bias
Deviation of results or inferences from the truth, or processes leading to such deviation
Case-Control Study
Retrospective comparison of exposures of persons with disease to those of persons without the disease
Cohort Study
Prospective of exposed and non-exposed defined groups, with a comparison of disease rates during the time covered
Dose-Response Relationship
A relationship in which change in amount, intensity, or duration of exposure is associated with a change - either an increase or decrease - in risk of a specific outcome
Determinant
Any definable factor that effects a change in health condition or other characteristic
Incidence
The number of new cases of illness commencing, or of persons falling ill, during a specified time period in a given population
Odds Ratio
A measure of the degree of association
Prevalence
The proportion of persons with a particular disease within a given population at a given time
Prognosis
The possible outcomes of a disease or condition and the likelihood that each one will occur
Relative Risk
The ratio of the probability of developing, in a specified period of time, an outcome among those receiving treatment or exposed to a risk factor, compared with the probability of developing the outcome if the risk factor or intervention is not present
Risk Factors
Patient characteristics or factors associated with an increased probability of developing a disease or condition