AGENT: A factor, such as a microorganism, chemical substance, or form of radiation, whose presence, excessive presence, or (in deficiency diseases) relative absence is essential for the occurrence of disease.
ASSESSMENT: One of public health’s three core functions. The regular collection, analysis and sharing of information about health conditions, risks and resources in a community. Assessment is needed to identify health problems and priorities and the resources available to address the priorities.
ASSOCIATION: Statistical relationship between two or more events, characteristics other variables.
BIAS: Deviation of results or inferences from the truth, or processes leading to such systematic deciation. Any trend in the collection, analysis, interpretation or review of data that can lead to conclusions that are systematically different from the truth
BIOLOGICAL TRANSMISSION: The indirect vector-borne transmission of an infectious agent in which the agent undergoes biologic changes within the vector before being transmitted to a new host.
BIOTERRORISM: The intentional use of any microorganism, virus, infectious substance, or biological product that may be engineered as a result of biotechnology, or any naturally occurring or bio-engineered component of any such microorganism, virus, infectious substance, or biological product, to cause death disease, or other biological malfunction in a human, an animal, a plant, or another living organism in order to influence the conduct of government or to intimidate or coerce a civilian population.
CARRIER.: A person or animal without apparent disease who harbors a specific infectious agent and is capable of transmitting the agent to others. The carrier state may occur in an individual with an infection that is in apparent throughout its course (known as asymptomatic carrier), or during the incubation period, convalescence, and post convalescence of an individual with a clinically recognizable disease. The carrier state may be of short or long duration (transient carrier or chronic carrier).
CASE DEFINITION: A set of standard criteria for deciding whether a person has a particular disease or health related condition, by specifying clinical criteria and limitations on time, place, and person.
CAUSE OF DISEASE: A factor (characteristic, behavior, event, etc.) that directly inuences the occurrence of disease. A reduction of the factor in the population should lead to a reduction in the occurrence of disease.
CHAIN OF INFECTION: A process that begins when an agent leaves its reservoir or host through a portal of exit, and is conveyed by some mode of transmission, then enters through an appropriate portal of entry to infect a susceptible host.
Chronic disease: A disease that has one or more of the following characteristics: it is permanent, leaves residual disability, is caused by a nonreversible pathological alteration, requires special training of the patient for rehabilitation, or may be expected to require a long period of supervision, observation or care.
CLUSTER. An aggregation of cases of a disease or other health-related condition, particularly cancer and birth defects, which are closely grouped in time and place are known as cluster. The number of cases may or may not exceed the expected number; frequently the expected number is not known
COMMON SOURCE OUTBREAK.: An outbreak that results from a group of persons being exposed to a common noxious influence, such as an infectious agent or toxin. If the group is exposed over a relatively brief period of time, so that all cases occur within one incubation period, then the common source outbreak is further classified as a point source outbreak. In some common source outbreaks, persons may be exposed over a period of days, weeks, or longer, with the exposure being either intermittent or continuous.
CONTACT.: Exposure to a source of an infection, or a person so exposed. CONTAGIOUS. Capable of being transmitted from one person to another by contact or close proximity.
DEMOGRAPHIC INFORMATION.: The person: characteristics—age, sex, race, and occupation—of descriptive epidemiology used to characterize the populations at risk.
DETERMINANTS of Health: Any factor, whether event, characteristic, or other denable entity, that brings about change in a health condition, or in other dened characteristics. The range of personal, social, economic and environmental factors that determine the health status of individuals or populations.
DIRECT TRANSMISSION. :The immediate transfer of an agent from a reservoir to a susceptible host by direct contact or droplet spread. DISTRIBUTION. In epidemiology, the frequency and pattern of health-related characteristics and events in a population. In statistics, the observed or theoretical frequency of values of a variable.
DROPLET NUCLEI. The residue of dried droplets that may remain suspended in the air for long periods, may be blown over great distances, and are easily inhaled into the lungs and exhaled.
DROPLET SPREAD. The direct transmission of an infectious agent from a reservoir to a susceptible host by spray with relatively large, short-ranged aerosols produced by sneezing, coughing, or talking.
DROPLET NUCLEI. The residue of dried droplets that may remain suspended in the air for long periods, may be blown over great distances, and are easily inhaled into the lungs and exhaled. DROPLET SPREAD. The direct transmission of an infectious agent from a reservoir to a susceptible host by spray with relatively large, short-ranged aerosols produced by sneezing, coughing, or talking.
ENVIRONMENTAL FACTOR. An extrinsic factor (geology, climate, insects, sanitation, health services, etc.) which aects the agent and the opportunity for exposure.
EPIDEMIC. The occurrence of more cases of disease than expected in a given area or among a specic group of people over a particular period of time.
EPIDEMIC CURVE. A histogram that shows the course of a disease outbreak or epidemic by plotting the number of cases by time of onset.
EPIDEMIC PERIOD. A time period when the number of cases of disease reported is greater than expected.
EPIDEMIOLOGIC TRIAD. The traditional model of infectious disease causation. Includes three components: an external agent, a susceptible host, and an environment that brings the host and agent together, so that disease occurs.
EPIDEMIOLOGY. The study of the distribution and determinants of health-related states or events in specied populations, and the application of this study to the control of health problems.
EXPOSED (GROUP). A group whose members have been exposed to a supposed cause of disease or health state of interest, or possess a characteristic that is a determinant of the health outcome of interest.
FREQUENCY DISTRIBUTION. A complete summary of the frequencies of the values or categories of a variable; often displayed in a two column table: the left column lists the individual values or categories, the right column indicates the number of observations in each category.
HEALTH DISPARITIES—Differences in morbidity and mortality due to various causes experience by specific sub-populations.
HYPOTHESIS. A supposition, arrived at from observation or reflection, that leads to refutable predictions. Any conjecture cast in a form that will allow it to be tested and refuted.
HOST FACTOR. An intrinsic factor (age, race, sex, behaviors, etc.) which influences an individual’s exposure, susceptibility, or response to a causative agent.
HYPOTHESIS, NULL. The first step in testing for statistical significance in which it is assumed that the exposure is not related to disease.
HYPOTHESIS, ALTERNATIVE. The hypothesis, to be adopted if the null hypothesis proves implausible, in which exposure is associated with disease.
IMMUNITY, ACTIVE: Resistance developed in response to stimulus by an antigen (infecting agent or vaccine) and usually characterized by the presence of antibody produced by the host.
IMMUNITY, HERD: The resistance of a group to invasion and spread of an infectious agent, based on the resistance to infection of a high proportion of individual members of the group. The resistance is a product of the number susceptible and the probability that those who are susceptible will come into contact with an infected person.
IMMUNITY, PASSIVE: Immunity conferred by an antibody produced in another host and acquired naturally by an infant from its mother or artificially by administration of an antibody-containing preparation (antiserum or immune globulin).
INCUBATION PERIOD; A period of subclinical or inapparent pathologic changes following exposure, ending with the onset of symptoms of infectious disease.
OBSERVATIONAL STUDY: Epidemiological study in situations where nature is allowed to take its course. Changes or differences in one characteristic are studied in relation to changes or differences in others, without the intervention of the investigator.
ODDS RATIO: A measure of association which quantifies the relationship between an exposure and health outcome from a comparative study; also known as the cross-product ratio.
ORDINAL SCALE. Classification into ordered qualitative categories; e.g., social class (I, II, III, etc.), where the values have a distinct order, but their categories are qualitative in that there is no natural (numerical) distance between their positive values.
PANDEMIC. An epidemic occurring over a very wide area (several countries or continents) and usually affecting a large proportion of the population.
POINT PREVALENCE. The amount of a particular disease present in a population at a single point in time.
PUBLIC HEALTH SURVEILLANCE. The systematic collection, analysis, interpretation, and dissemination of health data on an ongoing basis, to gain knowledge of the pattern of disease occurrence and potential in a community, in order to control and prevent disease in the community.
SAMPLE. A selected subset of a population. A sample may be random or non-random and it may be representative or non-representative.
SECONDARY ATTACK RATE. A measure of the frequency of new cases of a disease among the contacts of known cases.
YEARS OF POTENTIAL LIFE LOST—A measure of the effects of disease or injury in a population that calculates years of life lost before a specific age (often ages 64 or 75). This approach places additional value on deaths that occur at earlier ages.
ZOONOSES. An infectious disease that is transmissible under normal conditions from animals to humans.