“Epidemic”的意思、由来-开放百科全书

An epidemic (from Greek ἐπί epi "upon or above" and δῆμος demos "people") is the rapid spread of infectious disease to a large number of people in a given population within a short period of time, usually two weeks or less. For example, in meningococcal infections, an attack rate in excess of 15 cases per 100,000 people for two consecutive weeks is considered an epidemic.^[1]^[1]

Epidemics of infectious disease are generally caused by several factors including a change in the ecology of the host population (e.g. increased stress or increase in the density of a vector species), a genetic change in the pathogen reservoir or the introduction of an emerging pathogen to a host population (by movement of pathogen or host). Generally, an epidemic occurs when host immunity to either an established pathogen or newly emerging novel pathogen is suddenly reduced below that found in the endemic equilibrium and the transmission threshold is exceeded.^[2]

An epidemic may be restricted to one location; however, if it spreads to other countries or continents and affects a substantial number of people, it may be termed a pandemic.^[3] 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.^[1] 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

There are several changes that may occur in an infectious agent that may trigger an epidemic. These include:^[3]{{rp|55}}

An epidemic disease is not required to be contagious,^[1]^[8] and the term has been applied to West Nile fever^[1] and the obesity epidemic (e.g. by the World Health Organisation^[4]), among others.^[8]

The conditions which govern the outbreak of epidemics include infected food supplies such as contaminated drinking water and the migration of populations of certain animals, such as rats or mosquitoes, which can act as disease vectors. Certain epidemics occur at certain seasons.

For example, whooping-cough occurs in spring, whereas measles produces two epidemics, one in winter and one in March. Influenza, the common cold, and other infections of the upper respiratory tract, such as sore throat, occur predominantly in the winter.

There is another variation, both as regards the number of people affected and the number who die in successive epidemics: the severity of successive epidemics rises and falls over periods of five or ten years.^[5]

Types

Common source outbreak

In a common source outbreak epidemic, 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.^[3]{{rp|56}}

Propagated outbreak

In a propagated outbreak, the disease spreads person-to-person. Affected individuals may become independent reservoirs leading to further exposures.^[3]{{rp|56}}

Many epidemics will have characteristics of both common source and propagated outbreaks (sometimes referred as mixed outbreak).

For example, secondary person-to-person spread may occur after a common source exposure or an environmental vectors may spread a zoonotic diseases agent.^[3]{{rp|56–58}}

Transmission

Response

Experts{{Who|date=March 2019}} suggest that the best way to prepare for an epidemic is to have a disease surveillance system, be able to quickly dispatch emergency workers, especially local-based emergency workers, and have a legitimate way to guarantee the safety and health of health workers.^[7]

Effective preparations for a response to a pandemic are multi-layered. The first layer is a disease surveillance system. Tanzania, for example, runs a national lab that runs testing for 200 health sites and tracks the spread of infectious diseases. The next layer is the actual response to an emergency. According to U.S.-based columnist Michael Gerson, only the U.S. military and NATO have the global capability to respond to such an emergency.^[7]

Gates proposed that the world responded slowly to the Ebola virus outbreak because of a lack of preparation. Two weeks after the 2013 typhoon hit the Philippines, over 150 foreign medical teams were on the ground helping with injured victims. After the 2005 earthquake in Pakistan, a team of aid workers who had been helping Afghan refugees for several decades were able to get to the victims in less than 24 hours. Dr. Bruce Aylward, assistant director general for emergencies at the World Health Organization, says that in the case of the Ebola outbreak, "there was no way anyone could guarantee the right of medical evacuation for people affected by Ebola.”

The CDC will scale back global disease prevention efforts by 80 percent by October 2019 due to a lack of funding (as funding had been temporarily increased in 2014 to address the Ebola epidemic).^[8]

Etymology

The term epidemic derives from a word form attributed to Homer's Odyssey, which later took its medical meaning from the Epidemics, a treatise by Hippocrates.^[9] Before Hippocrates, epidemios, epidemeo, epidamos, and other variants had meanings similar to the current definitions of "indigenous" or "endemic."^[9] Thucydides' description of the Plague of Athens is considered one of the earliest accounts of a disease epidemic.^[9] By the early 17th century, the terms endemic and epidemic referred to contrasting conditions of population-level disease, with the endemic condition at low rates of occurrence and the epidemic condition widespread.^[10]

See also

References

1. ^¹²³{{cite journal |author1=Green MS |author2=Swartz T |author3=Mayshar E |author4=Lev B |author5=Leventhal A |author6=Slater PE |author7=Shemer Js |title=When is an epidemic an epidemic? |journal=Isr. Med. Assoc. J. |volume=4 |issue=1 |pages=3–6 |date=January 2002 |doi= |pmid=11802306}}
2. ^"epidemic". The Encyclopedia of Ecology and Environmental Management, Blackwell Science. Oxford: Blackwell Publishers, 1998. Credo Reference. Web. 17 September 2012.
3. ^¹²³⁴⁵{{cite book |title=Principles of Epidemiology, Third Edition |publisher=Centers for Disease Control and Prevention |location=Atlanta, Georgia |year=2012|pages= |isbn= |oclc= |doi= |url=https://www.cdc.gov/ophss/csels/dsepd/ss1978/ss1978.pdf}}
4. ^Controlling the global obesity epidemic, the World Health Organisation
5. ^"Epidemic." Black's Medical Dictionary, 42nd Edition. London: A&C Black, 201e. Web. 17 September 2012.
6. ^"transmission." Saunders Comprehensive Veterinary Dictionary. Philadelphia: Elsevier Health Sciences, 2007. Credo Reference. Web. 17 September 2012.
7. ^¹{{cite news|last1=Gerson|first1=Michael|title=The next epidemic|work=The Greenville News|date=30 March 2015|location=South Carolina, US}}
8. ^{{cite web|url=http://thehill.com/homenews/administration/371961-cdc-to-cut-global-disease-prevention-efforts-by-80-percent|title=CDC to cut global disease prevention efforts by 80 percent|first=Jacqueline|last=Thomsen|date=2 February 2018}}
9. ^¹²³⁴{{cite journal |vauthors=Martin PM, Martin-Granel E |title=2,500-year evolution of the term epidemic |journal=Emerging Infect. Dis. |volume=12 |issue=6 |pages=976–80 |date=June 2006 |pmid=16707055 |doi= 10.3201/eid1206.051263|url=http://wwwnc.cdc.gov/eid/content/12/6/pdfs/v12-n6.pdf |pmc=3373038}}
10. ^{{cite book|last=Lodge|first=T.|title=A treatise of the plague: containing the nature, signes, and accidents of the same, with the certaine and absolute cure of the fevers, botches and carbuncles that raigne in these times|year=1603|publisher=Edward White|location=London}}