Ajay Kumar: Created a new article

2023-08-29T17:39:03Z

Created a new article

New page

{{Other uses}}
{{Short description|Rapid spread of disease affecting a large number of people in a short time}}
[[File:2014 West Africa Ebola Epidemic - New Cases per Week.svg|thumb|upright=1.5|Example of an epidemic showing the number of new infections over time.]]
An '''epidemic''' (from [[Ancient Greek|Greek]] ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of [[disease]] to a large number of hosts in a given population within a short period of time. For example, in [[meningococcal infection]]s, an [[attack rate]] in excess of 15 cases per 100,000 people for two consecutive weeks is considered an epidemic.<ref name="Principles of Epidemiology"/><ref name=Green>{{cite journal | vauthors = Green MS, Swartz T, Mayshar E, Lev B, Leventhal A, Slater PE, Shemer J | title = When is an epidemic an epidemic? | journal = The Israel Medical Association Journal | volume = 4 | issue = 1 | pages = 3–6 | date = January 2002 | pmid = 11802306 | url = https://www.ima.org.il/FilesUploadPublic/IMAJ/0/55/27606.pdf }}</ref>

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.<ref>{{cite book | veditors = Callow PP | chapter = Epidemic | chapter-url = https://books.google.com/books?id=JKTeiqPBpM4C&pg=PA246 | title = The Encyclopedia of Ecology and Environmental Management | publisher = Blackwell Science Ltd. | location = Oxford | date = 1998 | pages = 246 | isbn = 0-86542-838-7 }}</ref>

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]].<ref name="Principles of Epidemiology">{{cite book |url= https://www.cdc.gov/csels/dsepd/ss1978/SS1978.pdf |title=Principles of Epidemiology | edition = Third |publisher= [[Centers for Disease Control and Prevention]] |year=2012 |location=Atlanta, Georgia }}</ref> The declaration of an epidemic usually requires a good understanding of a [[baseline (medicine)|baseline]] rate of [[incidence (epidemiology)|incidence]]; epidemics for certain diseases, such as [[influenza]], are defined as reaching some defined increase in incidence above this baseline.<ref name=Green/> 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. An epidemic can cause enormous damage through financial and economic losses in addition to impaired health and loss of life.{{cn|date=July 2023}}

==Definition==
The term epidemic derives from a word form attributed to [[Homer]]'s ''[[Odyssey]]'', which later took its medical meaning from the ''[[:s:Of the Epidemics|Epidemics]],'' a treatise by [[Hippocrates]].<ref name=Martin>{{cite journal | vauthors = Martin PM, Martin-Granel E | title = 2,500-year evolution of the term epidemic | journal = Emerging Infectious Diseases | volume = 12 | issue = 6 | pages = 976–80 | date = June 2006 | pmid = 16707055 | pmc = 3373038 | doi = 10.3201/eid1206.051263 }}</ref> Before Hippocrates, {{transl|grc|epidemios}}, {{transl|grc|epidemeo}}, {{transl|grc|epidamos}}, and other variants had meanings similar to the current definitions of "indigenous" or "[[Endemic (epidemiology)|endemic]]".<ref name=Martin/> [[Thucydides]]' description of the [[Plague of Athens]] is considered one of the earliest accounts of a disease epidemic.<ref name=Martin/> 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.<ref name=Lodge1603>{{cite book| vauthors = Lodge 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|url=https://archive.org/details/b3032810x|year=1603|publisher=Edward White|location=London}}</ref> The term "epidemic" has become emotionally charged.<ref name="Green"/>

The [[Centers for Disease Control and Prevention]] defines epidemic broadly: "the occurrence of more cases of disease, injury, or other health condition than expected in a given area or among a specific group of persons during a particular period. Usually, the cases are presumed to have a common cause or to be related to one another in some way (see also outbreak)."<ref name="Principles of Epidemiology"/> The terms "epidemic" and "outbreak" have often been used interchangeably. Researchers Manfred S. Green and colleagues propose that the latter term be restricted to smaller events, pointing out that ''[[Chambers Dictionary|Chambers Concise Dictionary]]'' and ''[[Stedman's Medical Dictionary]]'' acknowledge this distinction.<ref name=Green/>

===Epidemic wave===
The concept of waves in epidemics has gained huge popularity and profound implications especially in the COVID context and the 1918 influenza epidemic. For instance, the American top federal infectious disease expert, Anthony Fauci, warned that: “People keep talking about a second wave,” but “we’re still in a first wave”. A working scientific definition for the term "epidemic wave" is based on two key features: 1) an epidemic wave comprises periods of upward and/or downward trends, and 2) these increases or decreases must be substantial and sustained over a period of time, in order to distinguish them from minor fluctuations or reporting errors.<ref name=Zhang>{{cite journal | author1 = Zhang Stephen X | author2 = Marioli Francisco Arroyo | author3 = Gao Renfei | author4 = Wang Senhu| title = When is an epidemic an epidemic? | journal = Risk Management and Healthcare Policy | volume = 14 | pages = 3775–3782 | date = 2021 | doi = 10.2147/RMHP.S326051 | pmid = 34548826 | pmc = 8448159 | doi-access = free }}</ref> The use of a consistent scientific definition is to provide a consistent language that can be used to communicate about and understand the progression of the COVID-19 pandemic, which would aid healthcare organizations and policymakers in resource planning and allocation.

==Causes==
[[File:Plague in an Ancient City LACMA AC1997.10.1 (1 of 2).jpg|thumb|upright=1.25|''The Plague of Athens'' ({{Circa|1652}}–1654) by [[Michiel Sweerts]], illustrating the [[Plague of Athens|devastating epidemic that struck Athens in 430 BC]], as described by the historian [[Thucydides]]]]

There are several changes that may occur in an [[infectious agent]] that may trigger an epidemic. These include:<ref name="Principles of Epidemiology"/>{{rp|55}}
* Increased [[virulence]]
* Introduction into a novel setting
* Changes in host susceptibility to the infectious agent

An epidemic disease is not required to be [[contagious disease|contagious]],<ref name=Green/><ref name=Martin/> and the term has been applied to [[West Nile fever]]<ref name=Green/> and the [[obesity epidemic]] (e.g., by the World Health Organization<ref>[https://www.who.int/nutrition/topics/obesity/en/ Controlling the global obesity epidemic], the World Health Organization</ref>), among others.<ref name=Martin/>

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.{{cn|date=March 2023}}

Epidemics can be related to seasonality of certain infectious agents. Seasonality may enter into any of the eight key elements of the system: (1) susceptible recruitment via reproduction, (2) transmission, (3) acquired immunity and recovery, (4) waning immunity, (5) natural mortality, (6) symptomatology and pathology (which may be acute or chronic, depending on the disease), (7) disease-induced mortality, and (8) cross-species transmission.<ref>{{cite journal | vauthors = Martinez ME | title = The calendar of epidemics: Seasonal cycles of infectious diseases | journal = PLOS Pathogens | volume = 14 | issue = 11 | pages = e1007327 | date = November 2018 | pmid = 30408114 | pmc = 6224126 | doi = 10.1371/journal.ppat.1007327 | doi-access = free }}</ref> 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.<ref>{{cite book | veditors = Marcovitch H | chapter = Epidemic | chapter-url = https://books.google.com/books?id=09JaXjVdulgC&pg=PT706 | title = Black's Medical Dictionary | edition = 42nd | location = London | publisher = A&C Black | date = 2009 | isbn = 978-1-4081-4564-7 }}</ref>

==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.<ref name="Principles of Epidemiology"/>{{rp|56}}

===Propagated outbreak===
In a propagated outbreak, the disease spreads person-to-person. Affected individuals may become independent reservoirs leading to further exposures.<ref name="Principles of Epidemiology"/>{{rp|56}}Many epidemics will have characteristics of both common source and propagated outbreaks (sometimes referred to as '''mixed outbreak''').{{cn|date=February 2023}}

For example, secondary person-to-person spread may occur after a common source exposure or an environmental vector may spread a [[zoonotic]] diseases agent.<ref name="Principles of Epidemiology"/>{{rp|56–58}}

==Transmission==
* Airborne transmission: Airborne transmission is the spread of infection by droplet nuclei or dust in the air. Without the intervention of winds or drafts the distance over which airborne infection takes place is short, say 10 to 20 feet.<ref name="ACAIM-WACEM COVID-19 Consensus Paper">{{cite journal | vauthors = Stawicki SP, Jeanmonod R, Miller AC, Paladino L, Gaieski DF, Yaffee AQ, De Wulf A, Grover J, Papadimos TJ, Bloem C, Galwankar SC, Chauhan V, Firstenberg MS, Di Somma S, Jeanmonod D, Garg SM, Tucci V, Anderson HL, Fatimah L, Worlton TJ, Dubhashi SP, Glaze KS, Sinha S, Opara IN, Yellapu V, Kelkar D, El-Menyar A, Krishnan V, Venkataramanaiah S, Leyfman Y, Saoud Al Thani HA, Wb Nanayakkara P, Nanda S, Cioè-Peña E, Sardesai I, Chandra S, Munasinghe A, Dutta V, Dal Ponte ST, Izurieta R, Asensio JA, Garg M | display-authors = 6 | title = The 2019-2020 Novel Coronavirus (Severe Acute Respiratory Syndrome Coronavirus 2) Pandemic: A Joint American College of Academic International Medicine-World Academic Council of Emergency Medicine Multidisciplinary COVID-19 Working Group Consensus Paper | journal = Journal of Global Infectious Diseases | volume = 12 | issue = 2 | pages = 47–93 | year = 2020 | pmid = 32773996 | pmc = 7384689 | doi = 10.4103/jgid.jgid_86_20 | url = https://www.researchgate.net/publication/340903626 | s2cid = 218754925 | doi-access = free }}</ref>
* Arthropod transmission: Arthropod transmission takes place by an insect, either mechanically through a contaminated proboscis or feet, or biologically when there is growth or replication of an organism in the arthropod.{{cn|date=March 2023}}
* Biological transmission: Involving a normal biological process, e.g., passing a stage of development of the infecting agent in an intermediate host. Opposite to mechanical transmission.{{cn|date=March 2023}}
* Contact transmission: The disease agent is transferred directly by biting, sucking, chewing or indirectly by inhalation of droplets, drinking of contaminated water, traveling in contaminated vehicles.
* Cyclopropagative transmission: The agent undergoes both development and multiplication in the transmitting vehicle.{{cn|date=March 2023}}
* Developmental transmission: The agent undergoes some development in the transmission vehicle.{{cn|date=March 2023}}
* Fecal-oral transmission: The infectious agent is shed by the infected host in feces and acquired by the susceptible host through the ingestion of contaminated material.
* Horizontal transmission: Lateral spread to others in the same group and at the same time; spread to contemporaries.
* Propagative transmission: The agent multiplies in the transmission vehicle.
* Vertical transmission: From one generation to the next, perhaps transovarially or by intrauterine infection of the fetus. Some retroviruses are transmitted in the germline, i.e. their genetic material is integrated into the DNA of either the ovum or sperm.<ref>{{cite book | veditors = Studdert VP, Gay CC, Charles Blood DC | chapter = Transmission | title = Saunders Comprehensive Veterinary Dictionary | location = Philadelphia | publisher = Elsevier Health Sciences | date = 2012 | edition = 4th | isbn = 978-0-7020-3231-8 }}</ref>

==Preparation==

Preparations for an epidemic include having a disease surveillance system; the ability to quickly dispatch emergency workers, especially local-based emergency workers; and a legitimate way to guarantee the safety and health of health workers.<ref name=gerson>{{cite news | vauthors = Gerson M | url = https://www.washingtonpost.com/opinions/the-next-epidemic/2015/03/26/aee9f344-d3e8-11e4-a62f-ee745911a4ff_story.html | title = The next epidemic | newspaper = [[The Washington Post]] | date = 26 March 2015 }}</ref><ref>{{cite journal | vauthors = Gates B | title = The next epidemic--lessons from Ebola | journal = The New England Journal of Medicine | volume = 372 | issue = 15 | pages = 1381–4 | date = April 2015 | pmid = 25853741 | doi = 10.1056/NEJMp1502918 | author-link = Bill Gates | doi-access = free }}</ref>

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 in 2015, only the U.S. military and [[NATO]] have the global capability to respond to such an emergency.<ref name=gerson /> Still, despite the most extensive preparatory measures, a fast-spreading pandemic may easily exceed and overwhelm existing health-care resources.<ref name="ACAIM-WACEM COVID-19 Consensus Paper"/> Consequently, early and aggressive mitigation efforts, aimed at the so-called "epidemic curve flattening" need to be taken.<ref name="ACAIM-WACEM COVID-19 Consensus Paper"/> Such measures usually consist on non-pharmacological interventions such as social/physical distancing, aggressive contact tracing, "stay-at-home" orders, as well as appropriate personal protective equipment (i.e., masks, gloves, and other physical barriers to spread).<ref name="ACAIM-WACEM COVID-19 Consensus Paper"/>

== See also ==
{{Portal|Pandemics|Medicine}}
{{div col |colwidth=25em |small=no}}
* [[List of epidemics]]
* [[Epidemiology]]
* [[Endemic (epidemiology)]]
* [[Pandemic]]
* [[Syndemic]]
* [[European Centre for Disease Prevention and Control]]
* [[Centers for Disease Control and Prevention|Center for Disease Control (USA)]]
* [[Mathematical modelling of infectious disease]]
* [[Compartmental models in epidemiology|Epidemic model]]
* [[Biosecurity]]
{{div col end}}

== References ==
{{reflist}}

== Further reading ==
{{external media| float = right| video1 = [https://www.c-span.org/video/?458488-1/influenza Presentation by Brown on ''Influenza'', March 5, 2019], [[C-SPAN]]}}
{{refbegin}}
* {{cite web|author=American Lung Association|author-link=American Lung Association|date=April 2007|title=Multidrug Resistant Tuberculosis Fact Sheet|url=http://www.lungusa.org/site/pp.aspx?c=dvLUK9O0E&b=35815|access-date=29 November 2007|url-status=dead|archive-url=https://web.archive.org/web/20061130122651/http://www.lungusa.org/site/pp.aspx?c=dvLUK9O0E&b=35815|archive-date=30 November 2006}}
* {{cite journal|author=Bancroft, EA|title=Antimicrobial resistance: it's not just for hospitals|journal=JAMA|volume=298|issue=15|pages=1803–04|date=October 2007|doi=10.1001/jama.298.15.1803|pmid=17940239|pmc=2536104}}
* Brook, Timothy; et al. "Comparative pandemics: the Tudor–Stuart and Wanli–Chongzhen years of pestilence, 1567–1666" ''Journal of Global History'' (2020) 14#3 pp 363–379 emphasis on Chinese history, compared to England
* {{cite book | vauthors=Brown J |title=Influenza: The Hundred Year Hunt to Cure the Deadliest Disease in History|publisher=Atria|location=New York |year=2018 |isbn=978-1501181245}}
* Eisenberg, Merle, and Lee Mordechai. "The Justinianic Plague and Global Pandemics: The Making of the Plague Concept." ''American Historical Review'' 125.5 (2020): 1632–1667.
* {{Cite news |last=Honigsbaum |first=Mark |date=18 October 2020 |title=How do pandemics end? In different ways, but it's never quick and never neat |language=en-GB |work=The Guardian |url=https://www.theguardian.com/commentisfree/2020/oct/18/how-do-pandemics-end-in-different-ways-but-its-never-quick-and-never-neat |access-date=28 October 2020 |issn=0261-3077}}
* {{cite journal|author=Larson, E|title=Community factors in the development of antibiotic resistance|journal=Annual Review of Public Health|volume=28|pages=435–47|year=2007|pmid=17094768|doi=10.1146/annurev.publhealth.28.021406.144020|doi-access=free}}
* {{cite journal |last=Lietaert Peerbolte |first=Bert Jan |date=September 2021 |title=The Book of Revelation: Plagues as Part of the Eschatological Human Condition |journal=[[Journal for the Study of the New Testament]] |publisher=[[SAGE Publications]] |volume=44 |issue=1 |pages=75–92 |doi=10.1177/0142064X211025496
|doi-access=free |issn=1745-5294 |s2cid=237332665 }}
* [[Maryn McKenna|McKenna, Maryn]], "Return of the Germs: For more than a century drugs and vaccines made astounding progress against infectious diseases. Now our best defenses may be social changes", ''[[Scientific American]]'', vol. 323, no. 3 (September 2020), pp. 50–56. "What might prevent or lessen [the] possibility [of a virus emerging and finding a favorable human host] is more prosperity more equally distributed – enough that villagers in South Asia need not trap and sell bats to supplement their incomes and that, low-wage workers in the U.S. need not go to work while ill because they have no sick leave." (p. 56.)
* [[David Quammen|Quammen, David]], "The Sobbing Pangolin: How a threatened animal may be linked to the [Covid-19] pandemic's beginnings", ''[[The New Yorker]]'', 31 August 2020, pp. 26–31. "More field research is needed [...]. More sampling of wild animals. More scrutiny of genomes. More cognizance of the fact that animal infections can become human infections because humans are animals. We live in a world of viruses, and we have scarcely begun to understand this one [ [[COVID-19]] ]. (p. 31.)
* {{cite web |url=https://ipbes.net/pandemics |title=Escaping the 'Era of Pandemics': Experts Warn Worse Crises to Come Options Offered to Reduce Risk |author=|date=2020|publisher=[[Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services]]}}
{{refend}}

== External links ==
{{Wiktionary|epidemic}}
{{refbegin}}
* {{cite web | url = http://www.ecdc.europa.eu | title = European Centre for Disease Prevention and Control }}
* {{cite web | url = http://www.dundee.ac.uk/iea/ | title = International Epidemiological Association (IEA) | archive-url = https://web.archive.org/web/20101127143509/http://www.dundee.ac.uk/iea/ | archive-date = 2010-11-27 }}
* {{cite book | url = https://global.oup.com/academic/product/a-dictionary-of-epidemiology-9780199976720 | title = A Dictionary of Epidemiology (IEA) | date = 20 June 2014 | publisher = Oxford University Press | isbn = 978-0-19-997672-0 }}
* {{cite web | url = http://www.epidemiology.ch/history/betaversion.htm | title = People's Epidemiology Library | archive-url = https://web.archive.org/web/20120323082628/http://www.epidemiology.ch/history/betaversion.htm | archive-date = 2012-03-23 }}
* {{cite web | url = http://www.laprp.com/article.php?aid=348 | title = Video Discussion of the Prostate Cancer Epidemic }}
* {{cite web | url = http://vlab.infotech.monash.edu.au/simulations/cellular-automata/epidemic/ | work = Monash Virtual Laboratory | title = Simulations of epidemic spread across a landscape | archive-url = https://web.archive.org/web/20071104183725/http://vlab.infotech.monash.edu.au/simulations/cellular-automata/epidemic/ | archive-date = 2007-11-04 }}
{{refend}}

{{Concepts in infectious disease}}
{{Public health}}
{{Epidemics}}
{{Authority control}}

[[Category:Epidemics| ]]
[[Category:Biological hazards]]

Epidemic - Revision history

TabathaLea97053: adjust article per sources

Ajay Kumar: Created a new article