Epidemic
An epidemic is a disease that appears as new cases in the population in a period of time at a rate (the number of new cases in the population during a specified period of time is called the incidence rate) that substantially exceeds what is "expected," based on recent experence. It is therefore a somewhat subjective category and depends on what is "expected." An epidemic may be restricted to one locale (an outbreak), more general (an "epidemic") or even global (pandemic). Because it is based on what is "expected" or thought normal, a few cases of a very rare disease like rabies may be classified as an "epidemic," while many cases of a common disease (like the common cold) would not. Common diseases that occur at a constant but relatively high rate in the population are said to be "endemic." An example of an endemic disease is malaria in some parts of Africa (for example, Liberia) in which a large portion of the population is expected to get malaria sometime in their lifetime.
Famous examples of epidemics include the bubonic plague epidemic of Mediaeval Europe known as the Black Death, the Great Influenza Pandemic concurring with the end of World War I, and the current AIDS epidemic, which some also consider to be of pandemic proportions.
Non-biological usage
The term is often used in a non-biological sense to refer to widespread and growing societal problems, for example, in discussions of mental illness or drug addiction.
 | This medical article is a stub. You can help Wikipedia by expanding it. |