For other uses, see Epidemic (disambiguation) . An epidemic (from Greek ἐπί epi upon or above and δῆμος demos people) is the rapid spread of infectious disease to a large number of people in a given population within a short period of time, usually two weeks or less.efore Hippocrates, epidemios, epidemeo, epidamos, and other variants had meanings similar to the current definitions of indigenous or  endemic .. Thucydides ' description of the Plague of Athens is considered one of the earliest accounts of a disease epidemic.