In epidemiology, an infection that is epidemic (from Greek epi- upon + demos people) 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 analogous circumstance within an animal population.) In recent usages, the disease is not required to be communicable.
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Defining an epidemic can be subjective, depending in part on what is "expected". An epidemic may be restricted to one local (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 low 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 at some point in their lifetimes.
The term "epidemic" is often used in a sense to refer to widespread and growing societal problems, for example, in discussions of obesity, mental illness or drug addiction. It can also be used metaphorically to relate a type of problem like those mentioned above.
Famous examples of epidemics include HIV (present), the bubonic plague epidemic of Medieval Europe, known as the Black Death, and the Great Influenza Pandemic which coincided with the end of World War I.
Factors that have been described by Mark Woolhouse and Sonya Gowtage-Sequeria to stimulate the rise of new epidemics [1] include:
Several other factors have also been mentioned in different reports, such as the report by professor Andy Dobson [2] and the report by professor Akilesh Mishra [3].These include :
To protect us against the emergence of new epidemics, several preemptive measures have been proposed by the World Health Organisation [4].
In August 2007, the World Health Organization reported an unprecedented rate of propagation of infectious diseases.[5]