Epidemic

An epidemic is a marked increase in the number of cases of a disease relative to the expected number of cases. Epidemic disease is sometimes contrasted with endemic disease, which is the expected or usual incidence of disease in a location. While the term endemic is typically confined to infectious diseases, the term epidemic is more widely used. Endemic can refer to either the usually observed rate of disease or simply the fact that a disease is present in a locale. For example, hantavirus is endemic to many parts of the United States. A rate of disease that is endemic on one country would constitute an epidemic if it occurred in a country where the disease is ordinarily less common.

The terms outbreak and epidemic are ...