n epidemiology, an epidemic (from επί (epi), meaning "upon or above" and δήμος (demos), meaning "people") occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience.[1]:354[2] Epidemiologists often consider the term outbreak to besynonymous to epidemic, but the general public typically perceives outbreaks to be more local and less serious than epidemics.[2][1]:55, 354
Epidemics of infectious disease are generally caused by a change in the ecology of the host population (e.g. increased stress or increase in the density of a vector species), a genetic change in the parasite population or the introduction of a new parasite to a host population (by movement of parasites or hosts). Generally, an epidemic occurs when host immunity to a parasite population is suddenly reduced below that found in the endemic equilibrium and the transmission threshold is exceeded.[3]
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An epidemic may be restricted to one location; however, if it spreads to other countries or continents and affects a substantial number of people, it may be termed a pandemic.[1]:55The declaration of an epidemic usually requires a good understanding of a baseline rate of incidence; epidemics for certain diseases, such as influenza, are defined as reaching some defined increase in incidence above this baseline.[2] A few cases of a very rare disease may be classified as an epidemic, while many cases of a common disease (such as the common cold) would not. http://www.studymode.com/subjects/anglo-american-plc-in-south-africa-what-do-you-do-when-cost-reach-epidemic-proportions-page1.html -------------------------------------------------

The flu outbreak has reached epidemic proportions.
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