epidemic, outbreak of disease that affects a much greater number of people than is usual for the locality or that spreads to regions where it is ordinarily not present. A disease that tends to be restricted to a particular region (endemic disease) can become epidemic if nonimmune persons are present in large numbers (as in time of war or during pilgrimages), if the infectious agent is more virulent than usual, or if distribution of the disease is more easily effected. Cholera and plague, endemic in parts of Asia, can become epidemic under the above conditions, as can dysentery and many other infections. Epidemics, often now simply called "outbreaks" by epidemiologists, may also be caused by new disease agents in the human population, such as the Ebola virus. A worldwide epidemic is known as a pandemic, e.g., the influenza pandemic of 1918 or the AIDS pandemic beginning in the 1980s. Officially, the World Health Organization considers any disease outbreak that is spreading unchecked in two different regions of the worlds to be a pandemic; classification as a pandemic is not an indicator of the severity of a disease. A disease is said to be sporadic when only a few cases occur here and there in a given region. Epidemic disease is controlled by various measures, depending on whether transmission is through respiratory droplets, food and water contaminated with intestinal wastes, insect vectors, or other means. The Centers for Disease Control and Prevention tracks epidemics in the United States.

See also epdemiology.

In epidemiology, an epidemic (from Greek epi- upon + demos people) is a classification of 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 analogous circumstance within an animal population.) In recent usages, the disease is not required to be communicable.


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.

Endemic diseases

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 at some point in their lifetimes.

Non-infectious disease usage

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.

Notable epidemics through history

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 stimulating new epidemics

Factors that have been described by Mark Woolhouse and Sonya Gowtage-Sequeria to stimulate the rise of new epidemics include:

  1. Alterations in agricultural practices and land use
  2. Changes in society and human demographics
  3. Poor population health (e.g. malnutrition, HIV, ...)
  4. Hospitals and medical procedures
  5. Evolution of the pathogen (e.g. increased virulence, drug resistance,)
  6. Contamination of water supplies and food sources
  7. International travel
  8. Failure of public health programs
  9. International trade
  10. Climate change

Several other factors have also been mentioned in different reports, such as the report by professor Andy Dobson and the report by professor Akilesh Mishra .These include :

  1. Reduced levels of biodiversity (e.g. through environmental destruction)
  2. Bad urban planning

Pre-emptive measures

To protect us against the emergence of new epidemics, several preemptive measures have been proposed the World Health Organization .

Renewed concern

In August 2007, the World Health Organization reported an unprecedented rate of propagation of infectious diseases.


See also

External links

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