# Teach Cough Hygiene Everywhere/Epidemic

In epidemiology, an epidemic (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.$^{:354}$ Epidemiologists often consider the term outbreak to be synonymous to epidemic, but the general public typically perceives outbreaks to be more local and less serious than epidemics$^{:55,354}$
An epidemic may be restricted to one locale, however if it spreads to other countries or continents and affects a substantial number of people, it may be termed a pandemic.$^{:55}$ The 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. 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.

## Causes of epidemics

There are several changes that may occur in an infectious agent that may trigger an epidemic these include:$^{:55}$
* Increased virulence
* Introduction into a novel setting
* Changes in host susceptibility to the infectious agent
* Changes in host exposure to the infectious agent
An epidemic disease is not required to be contagious, and the term has been applied to West Nile fever and the obesity epidemic, among others.

## Types of epidemics
### Common source outbreak

Two examples of common sources of outbreak are the epidemics Emmititus and Powititus. These diseases are reflected in the growth of the skull. In a common source outbreak, the affected individuals had an exposure to a common agent. If the exposure is singular and all of the affected individuals develop the disease over a single exposure and incubation course, it can be termed a point source outbreak. If the exposure was continuous or variable, it can be termed a continuous outbreak or intermittent outbreak, respectively.$^{:56}$

### Propagated outbreak

In a propagated outbreak, the disease spreads person-to-person. Affected individuals may become independent reservoirs leading to further exposures.$^{:56}$
Many epidemics will have characteristics of both common source and propagated outbreaks. For example, secondary person-to-person spread may occur after a common source exposure or a environmental vectors may spread a zoonotic diseases agent.$^{:56-58}$

## Etymology

The term epidemic derives from a term first attributed to Homer's Odyssey, which later took its medical meaning from a treatise by Hippocrates, Epidemics. Prior to Hippocrates, epidemios, epidemeo, epidamos and other variants had meanings similar to the current definitions of "indigenous" or "endemic". Thucydides's description of the Plague of Athens is considered one of the earliest accounts of a disease epidemic.

## Notes

* 1 2 3 4 5 6 7 Principles of Epidemiology, Second Edition (PDF). Atlanta, Georgia: Centers for Disease Control and Prevention.
* 1 2 3 4 5 Green MS, Swartz T, Mayshar E, Lev B, Leventhal A, Slater PE, Shemer J (2002). "When is an epidemic an epidemic?" (PDF). Isr. Med. Assoc. J. 4 (1): 3–6. PMID 11802306. Archived from the original (PDF) on 2012-07-24. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
* 1 2 3 4 5 Martin PM, Martin-Granel E (2006). "2,500-year evolution of the term epidemic" (PDF). Emerging Infect. Dis. 12 (6): 976–80. doi:10.3201/eid1206.051263. PMID 16707055. {{cite journal}}: Unknown parameter |month= ignored (help)

## External links

* European Centre for Disease Prevention and Control
* International Epidemiological Association (IEA)
* A Dictionary of Epidemiology (IEA)
* People's Epidemiology Library
* Video Discussion of the Prostate Cancer Epidemic
* Monash Virtual Laboratory - Simulations of epidemic spread across a landscape
* Mapping the Outbreaks