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 experience. 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.

See also

• Endemic
• Epidemiology
• Pandemic
• Mathematical modelling in epidemiology
• List of epidemics
• Epizootic