Medical knowledge | Infectology » Introduction to Epidemiologic Terms

Source: http://www.doksinet Introduction to Epidemiologic Terms 1 Agent A biological, physical or chemical entity capable of causing disease Analytical Epidemiology Studies which identify and quantify associations, test hypotheses, and identify causes. Two common study types are cohort and case-control study. (compare with descriptive epidemiology) Antibody A protein, found in tissue fluids and blood, produced in response to the stimulus of a specific antigen and capable of combining with that antigen to neutralize or destroy it. Antigen That portion or product of a biological agent capable of stimulating the formation of specific antibodies. Attack rate A specific type of incidence, applied to a narrowly defined population observed for a limited period of time, such as during an epidemic. (see incidence, prevalence) Carrier A person or animal that harbors a specific infectious agent (but manifests no clinical disease) and is a source of infection for humans or animals. If the

infection leads to disease, the carrier state may occur during the incubation, convalescent, and post-convalescent periods. The carrier state may be of short or long duration (temporary carrier or chronic carrier). Case A person in a population or study group identified as having a particular disease or condition under investigation. A variety of criteria can be used to identify cases and is referred to as the case definition. Case-control study A type of observational analytic study. Enrollment into the study is based on presence (“case”) or absence (“control”) of disease. Characteristics or previous exposure to a factor of interest are then compared between cases and controls. 1 Comment: This document is only an introduction to epidemiologic terms, not a comprehensive list, or even a list of the most important terms. This list does not include terms, that are better described in diagrams, examples, or narratives, than in one or two sentences (such as 2x2 table,

confounding, bias, null hypothesis, sensitivity, specificity, predictive value, etc). Source: http://www.doksinet Epidemiology Terms Case Fatality Rate The proportion of cases of a specific condition fatal within a certain time frame: Number of deaths from a disease/Number of diagnosed cases of that disease (usually x 100). Causality The relationship between two variables whereby a change in one is followed by a change in the other. The criteria used to assess the likelihood of the causal nature of an association are its consistency, specificity, strength, temporal correctness and coherence (biological plausibility). Cohort study A type of observational analytic study. Inclusion in the study is based on exposure characteristics or membership in a group identified prior to development of disease, death, or other health-related outcomes. These outcomes are then subsequently ascertained and compared. Communicability (period of) The time during which a person or animal with

infectious disease is a potential source of infection. Descriptive Epidemiology Epidemiology concerned with organizing and summarizing health-related data according to time, place, and person. (See analytic epidemiology) Endemic The habitual presence of a disease or infectious agent within a geographic area or the prevalence of a given disease within such an area. Epidemic The occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time. (See outbreak) Epidemic Curve A graph or histogram that plots the distribution of cases by time. Epidemiology The study of the distribution and determinants of health-related events in specified populations, and the application of this study to control of health problems. Experimental Study A study in which the investigator specified the exposure category for each individual (clinical trial) or community (community trial), and then follows the individuals or community to

detect the effects of the exposure. Fomites A subclass of vehicles, including inanimate objects such as article of clothing, which may become contaminated and serve as a means of transmitting agents. Herd immunity The resistance of a group to invasion and spread of an infectious agent based on the immunity to a high proportion of individual members of the group. Hypothesis A supposition that can be tested and refuted. 2 Source: http://www.doksinet Epidemiology Terms Passive immunity Immunity attained either naturally (by maternal transfer) or artificially (by inoculation of specific protective antibodies – convalescent or immune serum, or immune serum globulin). Passive immunity is of brief duration, days or months. Active immunity Immunity that lasts months to years is attained either naturally (by infection), or artificially (by vaccination or immunization). Incidence rate The rate at which people without a disease develop the disease during a specified time period (see

prevalence, attack rate) Incubation period The time interval between the receipt of infection and the onset of illness. Index case The first case to occur among a number of similar cases, which are epidemiologically related. Index cases are often identified as a source of contamination or source of infection for subsequent cases. Latent period The interval in time from exposure to chemical agents and the onset of signs and symptoms of the illness. Morbidity The condition of being sick or diseased. Mortality rate The number of deaths from a given condition in a defined population in a specified time period. Observational Study Study that does not involve any intervention. The investigator observes the subjects and then records and analyzes the results. Odds ratio A measure of the strength of an association identified in a case control study. The odds ratio is an approximation of the true relative risk Outbreak Synonymous with epidemic (more cases of disease than expected in a

given area or among a specific group of people over a particular period of time). Sometimes the preferred word, since it may be less sensational. Pandemic A widespread epidemic disease affecting several countries or continents. Pathogenicity The capacity of an infectious agent to cause disease in a susceptible host. See also Virulence Precision Degree to which a measurement is sharply defined. (This can be independent of validity). 3 Source: http://www.doksinet Epidemiology Terms Prevalence The amount of a given disease existing at a given point in time (or period of time) in a community. (see incidence) Relative risk The ratio of the incidence rate of those exposed to a factor to the incidence rate of those not exposed: RR = incidence rate among those exposed incidence rate among those not exposed Relative risk is obtained directly from a cohort study and is a measure of the risk of disease associated with a particular exposure. Reservoir The habitat in which an infectious

agent normally lives, grows and multiplies; reservoirs may be humans, animals, or environmental. Secular trend Refers to changes over a long period of time, years or decades, which occur in both infectious and non-infectious conditions. Surveillance (in Public Health) The systematic collection, analysis, interpretation, and dissemination of health data on an ongoing basis, to gain knowledge of disease patterns to assist in disease prevention and control. Transmission The direct (contact or droplet spread) or indirect (vector-borne, vehicleborne, airborne) transfer of an infectious agent from a reservoir to a susceptible host. Validity Degree to which a measurement actually measures what it is supposed to measure. (This can be independent of precision) Vector An arthropod, which transfers an infectious agent from an infected to a susceptible host. Virulence The degree of pathogenicity of an infectious agent. Vital Statistics Data relating to birth, death, marriage, divorce, and

illness (morbidity). Zoonosis An infection or an infectious disease transmissible under natural conditions between animals and humans. 4