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.
Article Categories:Dictionary of Tropical Medicine