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Teach Cough Hygiene Everywhere/Epidemic

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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.[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

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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

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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.[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

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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]

Notes

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  1. ↑ a b c d e f g Principles of Epidemiology, Second Edition (PDF). Atlanta, Georgia: Centers for Disease Control and Prevention.
  2. ↑ a b c d e 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)
  3. ↑ a b c d e 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)
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