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An epidemic (from Greek ἐπί epi "upon or above" and δῆμος demos "people") is the rapid spread of disease to lớn a large number of hosts in a given population within a short period of time. 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.
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 mật độ trùng lặp từ khóa of a vector species), a genetic change in the pathogen reservoir or the introduction of an emerging pathogen to lớn a host population (by movement of pathogen or host). Generally, an epidemic occurs when host immunity to lớn 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.
An epidemic may be restricted to lớn one location; however, if it spreads to lớn other countries or continents and affects a substantial number of people, it may be termed a pandemic. 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. An epidemic can cause enormous damage through financial and economic losses in addition to lớn impaired health and loss of life.
The term epidemic derives from a word size attributed to lớn Homer's Odyssey, which later took its medical meaning from the Epidemics, a treatise by Hippocrates. Before Hippocrates, epidemios, epidemeo, epidamos, and other variants had meanings similar to lớn the current definitions of "indigenous" or "endemic". Thucydides' mô tả tìm kiếm of the Plague of Athens is considered one of the earliest accounts of a disease epidemic. By the early 17th century, the terms endemic and epidemic referred to lớn contrasting conditions of population-level disease, with the endemic condition at low rates of occurrence and the epidemic condition widespread. The term "epidemic" has become emotionally charged.
The Centers for Disease Control and Prevention defines epidemic broadly: "the occurrence of more cases of disease, injury, or other health condition kêu ca expected in a given area or among a specific group of persons during a particular period. Usually, the cases are presumed to lớn have a common cause or to lớn be related to lớn one another in some way (see also outbreak)." The terms "epidemic" and "outbreak" have often been used interchangeably. Researchers Manfred S. Green and colleagues propose that the latter term be restricted to lớn smaller events, pointing out that Chambers Concise Dictionary and Stedman's Medical Dictionary acknowledge this distinction.
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 lớn distinguish them from minor fluctuations or reporting errors. The use of a consistent scientific definition is to lớn provide a consistent language that can be used to lớn communicate about and understand the progression of the COVID-19 pandemic, which would aid healthcare organizations and policymakers in resource planning and allocation.
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 lớn the infectious agent
An epidemic disease is not required to lớn be contagious, and the term has been applied to lớn West Nile fever and the obesity epidemic (e.g., by the World Health Organization), among others.
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.
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Epidemics can be related to lớn 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. 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.
Common source outbreak
In a common source outbreak epidemic, the affected individuals had an exposure to lớn 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
In a propagated outbreak, the disease spreads person-to-person. Affected individuals may become independent reservoirs leading to lớn further exposures.: 56 Many epidemics will have characteristics of both common source and propagated outbreaks (sometimes referred to lớn as mixed outbreak).
For example, secondary person-to-person spread may occur after a common source exposure or an environmental vector may spread a zoonotic diseases agent.: 56–58
- 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 lớn đôi mươi feet.
- 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.
- Biological transmission: Involving a normal biological process, e.g., passing a stage of development of the infecting agent in an intermediate host. Opposite to lớn mechanical transmission.
- 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.
- Developmental transmission: The agent undergoes some development in the transmission vehicle.
- 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 lớn others in the same group and at the same time; spread to lớn contemporaries.
- Propagative transmission: The agent multiplies in the transmission vehicle.
- Vertical transmission: From one generation to lớn 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.
Preparations for an epidemic include having a disease surveillance system; the ability to lớn quickly dispatch emergency workers, especially local-based emergency workers; and a legitimate way to lớn guarantee the safety and health of health workers.
Effective preparations for a response to lớn 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 lớn an emergency. According to lớn U.S.-based columnist Michael Gerson in năm ngoái, only the U.S. military and NATO have the global capability to lớn respond to lớn such an emergency. Still, despite the most extensive preparatory measures, a fast-spreading pandemic may easily exceed and overwhelm existing health-care resources. Consequently, early and aggressive mitigation efforts, aimed at the so-called "epidemic curve flattening" need to lớn be taken. Such measures usually consist on non-pharmacological interventions such as social/physical distancing, aggressive tương tác tracing, "stay-at-home" orders, as well as appropriate personal protective equipment (i.e., masks, gloves, and other physical barriers to lớn spread).
- ^ a b c d e f g Principles of Epidemiology (PDF) (Third ed.). Atlanta, Georgia: Centers for Disease Control and Prevention. 2012.
- ^ a b c d e f Green MS, Swartz T, Mayshar E, Lev B, Leventhal A, Slater PE, Shemer J (January 2002). "When is an epidemic an epidemic?" (PDF). The Israel Medical Association Journal. 4 (1): 3–6. PMID 11802306.
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- ^ a b c d e Martin PM, Martin-Granel E (June 2006). "2,500-year evolution of the term epidemic". Emerging Infectious Diseases. 12 (6): 976–80. doi:10.3201/eid1206.051263. PMC 3373038. PMID 16707055.
- ^ Lodge T (1603). 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. London: Edward White.
- ^ Zhang Stephen X; Marioli Francisco Arroyo; Gao Renfei; Wang Senhu (2021). "When is an epidemic an epidemic?". Risk Management and Healthcare Policy. 14: 3775–3782. doi:10.2147/RMHP.S326051. PMC 8448159. PMID 34548826.
- ^ Controlling the global obesity epidemic, the World Health Organization
- ^ Martinez ME (November 2018). "The calendar of epidemics: Seasonal cycles of infectious diseases". PLOS Pathogens. 14 (11): e1007327. doi:10.1371/journal.ppat.1007327. PMC 6224126. PMID 30408114.
- ^ Marcovitch H, ed. (2009). "Epidemic". Black's Medical Dictionary (42nd ed.). London: A&C Black. ISBN 978-1-4081-4564-7.
- ^ a b c d Stawicki SP, Jeanmonod R, Miller AC, Paladino L, Gaieski DF, Yaffee AQ, et al. (2020). "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 of Global Infectious Diseases. 12 (2): 47–93. doi:10.4103/jgid.jgid_86_20. PMC 7384689. PMID 32773996. S2CID 218754925.
- ^ Studdert VP, Gay CC, Charles Blood DC, eds. (2012). "Transmission". Saunders Comprehensive Veterinary Dictionary (4th ed.). Philadelphia: Elsevier Health Sciences. ISBN 978-0-7020-3231-8.
- ^ a b Gerson M (26 March 2015). "The next epidemic". The Washington Post.
- ^ Gates B (April 2015). "The next epidemic--lessons from Ebola". The New England Journal of Medicine. 372 (15): 1381–4. doi:10.1056/NEJMp1502918. PMID 25853741.
|Presentation by Brown on Influenza, March 5, 2019, C-SPAN|
- American Lung Association (April 2007). "Multidrug Resistant Tuberculosis Fact Sheet". Archived from the original on 30 November 2006. Retrieved 29 November 2007.
- Bancroft, EA (October 2007). "Antimicrobial resistance: it's not just for hospitals". JAMA. 298 (15): 1803–04. doi:10.1001/jama.298.15.1803. PMC 2536104. PMID 17940239.
- 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 lớn England
- Brown J (2018). Influenza: The Hundred Year Hunt to lớn Cure the Deadliest Disease in History. New York: Atria. 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.
- Honigsbaum, Mark (18 October 2020). "How vì thế pandemics end? In different ways, but it's never quick and never neat". The Guardian. ISSN 0261-3077. Retrieved 28 October 2020.
- Larson, E (2007). "Community factors in the development of antibiotic resistance". Annual Review of Public Health. 28: 435–47. doi:10.1146/annurev.publhealth.28.021406.144020. PMID 17094768.
- Lietaert Peerbolte, Bert Jan (September 2021). "The Book of Revelation: Plagues as Part of the Eschatological Human Condition". Journal for the Study of the New Testament. SAGE Publications. 44 (1): 75–92. doi:10.1177/0142064X211025496. ISSN 1745-5294. S2CID 237332665.
- McKenna, Maryn, "Return of the Germs: For more kêu ca 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 lớn supplement their incomes and that, low-wage workers in the U.S. need not go to lớn work while ill because they have no sick leave." (p. 56.)
- Quammen, David, "The Sobbing Pangolin: How a threatened animal may be linked to lớn 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 lớn understand this one [ COVID-19 ]. (p. 31.)
- "Escaping the 'Era of Pandemics': Experts Warn Worse Crises to lớn Come Options Offered to lớn Reduce Risk". Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. 2020.
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