In epidemiology, an epidemic (from Greek epi- upon + demos people) is a disease that appears as new cases in a given human population, during a given period, at a rate that substantially exceeds what is "expected", based on recent experience (the number of new cases in the population during a specified period of time is called the "incidence rate"). (An epizootic is the same thing but for a nonhuman population.) Defining an epidemic can be subjective, depending in part on what is "expected". An epidemic may be restricted to one locale (an OutBreak), more general (an "EpidemIc") or even global (Pandemic).
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