A term applied to a disease that for most of the time is rare in a community but suddenly spreads rapidly to affect a large number of people. Epidemics of new strains of influenza are common. (See also endemic.)
A group of cases of a specific disease or illness clearly in excess of what one would normally expect in a particular geographic area. There is no absolute criterion for using the term epidemic; as standards and expectations change, so might the definition of an epidemic, e.g. an epidemic of violence.
Epidemic is a term applied to a disease which affects a large number of people in a particular locality at one time. The term is, in a sense, opposed to ENDEMIC, which means a disease always found in the locality in question. A disease may, however, be endemic as a rule – for example, MALARIA in swampy districts – and may become at times epidemic, when an unusually large number of people are affected. The rapid expansion of air travel has extended the scope for the spread of epidemic and endemic disease.
An epidemic disease is usually infectious from person to person, but not necessarily so since many persons in a locality may simply be exposed to the same cause at one time; for example, outbreaks of lead-poisoning are epidemic in this sense.
The conditions which govern the outbreak of epidemics are poorly understood, but include infected food supplies, such as drinking water contaminated by waste from people with CHOLERA or typhoid fever (see ENTERIC FEVER); milk infected with TUBERCLE bacillus; or ‘fast food’ products contaminated with salmonella. The migrations of certain animals, such as rats, are in some cases responsible for the spread of PLAGUE, from which these animals die in great numbers. Certain epidemics occur at certain seasons: for example, whooping-cough occurs in spring, whereas measles produces two epidemics – as a rule, one in winter and one in March. In?uenza, the common cold, and other infections of the upper respiratory tract, such as sore throat, occur predominantly in the winter.
There is another variation, both as regards the number of persons affected and the number who die in successive epidemics: the severity of successive epidemics rises and falls over periods of ?ve or ten years.
Unusual frequent occurrence of disease in the light of past experience. The occurrence in a community of region of a group of illness (or an outbreak) of similar nature, clearly in excess of normal expectancy and derived from a common or a propagated source. The number of cases indicating presence of an epidemic will vary according to the infectious agent, size and type of population exposed, previous experience or lack of exposure to the disease, time and place of occurrence. Epidemicity is thus relative to usual frequency of the disease in the same area, among the specified population, at the same season of the year. A single case of a communicable disease long absent from the population (as Smallpox, in Boston) or first invasion by a disease not previously recognised in the area (as American Trypanosomiasis, in Arizona) is to be considered sufficient evidence of an epidemic to require immediate reporting and full investigation.
n. a sudden outbreak of infectious disease that spreads rapidly through the population, affecting a large proportion of people. The commonest epidemics today are of influenza. Compare endemic; pandemic. —epidemic adj.
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