EPIDEMIC. A term used adjectivally or as a noun to sig nify the sudden outbreak of an infectious disease, of which the case incidence rises to a peak with more or less rapidity and thereafter declines, usually less rapidly. The curve thus formed shows variations in different diseases and in epidemics of the same disease. The mortality curve in any epidemic bears a general relation to the incidence curve, but the mortality curves in different epidemics of the same disease, like the incidence curves, may vary much in height and shape. (See EPIDEMIOLOGY.)