Epidemic

For other uses, see Epidemic (disambiguation).

In epidemiology, an epidemic (επι (epi)- meaning "upon or above" and δεμος (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.^[1]:354[2] 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^{[2][1]: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.^[1]: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.^[2] 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:^[1]: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,^[2][3] and the term has been applied to West Nile fever^[2] and the obesity epidemic, among others.^[3]

Types of epidemics

Common source outbreak

One example of a common source outbreak is the epidemic of Emmititus, the disease 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.^[1]:56

Propagated outbreak

In a propagated outbreak, the disease spreads person-to-person. Affected individuals may become independent reservoirs leading to further exposures.^[1]: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.^[1]: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.^[3] Prior to Hippocrates, epidemios, epidemeo, epidamos and other variants had meanings similar to the current definitions of "indigenous" or "endemic".^[3] Thucydides's description of the Plague of Athens is considered one of the earliest accounts of a disease epidemic.^[3]

See also

• List of epidemics
• Biosecurity
• Bugchasing and giftgiving
• Epidemic model
• Overpopulation
• Endemic (epidemiology)
• Syndemic

Organizations:

• Epi Info
• European Centre for Disease Prevention and Control
• OpenEpi

Notes

1. ^ ^{a b c d e f g} Principles of Epidemiology, Second Edition. Atlanta, Georgia: Centers for Disease Control and Prevention. http://www2a.cdc.gov/phtn/catalog/pdf-file/Epi_course.pdf. 
2. ^ ^{a b c d e} Green MS, Swartz T, Mayshar E, Lev B, Leventhal A, Slater PE, Shemer J (January 2002). "When is an epidemic an epidemic?". Isr. Med. Assoc. J. 4 (1): 3–6. PMID 11802306. http://www.ima.org.il/imaj/ar02jan-1.pdf. 
3. ^ ^{a b c d e} Martin PM, Martin-Granel E (June 2006). "2,500-year evolution of the term epidemic". Emerging Infect. Dis. 12 (6): 976–80. PMID 16707055. http://wwwnc.cdc.gov/eid/content/12/6/pdfs/v12-n6.pdf. 

External links

• Video Discussion of the Prostate Cancer Epidemic
• Monash Virtual Laboratory - Simulations of epidemic spread across a landscape
• Mapping the Outbreaks