Dictionary.net

Common to, or affecting at the same time, a large number in a community; - applied to a disease which, spreading widely, attacks many persons at the same time; as, an epidemic disease; an epidemic catarrh, fever, etc. See Endemic.

Common to, or affecting at the same time, a large number in a community; - applied to a disease which, spreading widely, attacks many persons at the same time; as, an epidemic disease; an epidemic catarrh, fever, etc. See Endemic.

That which falls at once upon great numbers of people, as a plague; generally prevailing, affecting great numbers; general, universal.