Epidemic

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This example of an epidemic of 2014 is showing the number of new infections at this time. 2014 West Africa Ebola Epidemic - New Cases per Week.svg
This example of an epidemic of 2014 is showing the number of new infections at this time.

An epidemic (from Greek ἐπί epi "upon or above" and δῆμος demos "people") is the rapid spread of disease to a large number of patients among a given population within an area in a short period of time.

Contents

Epidemics of infectious diseases are generally caused by several factors including a significant change in the ecology of the areal population (e.g., increased stress maybe additional reason or increase in the density of a vector species), the introduction of an emerging pathogen to an areal population (by movement of pathogen or host) or an unexpected genetic change that is in the pathogen reservoir.

Generally, epidemics concerns with the patterns of infectious disease spread. [1] An epidemic may occur 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.

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. [2] [3]

An epidemic may be restricted to one location within one country or further develop more locations in a country, however, if it spreads to other regional countries or even among continents but only if affects or threatens a substantial number of population, it may be overseen as within the terms of pandemic. [2] The registering and announcing of 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. [3] 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.

Definition

In medicine epidemics were well known and studied in 19th century. [4] We can trace the study of epidemics to late 18th century when this medical population studies emerged. [5]

However even early philosopher in Ancient Greece and Rome studied diseases and it was Hippocrates who first noticed that some diseases have epidemic type (he wrote on pestilence). [5] Galen also studied the epidemic diseases and how they appear. [5]

It is possible to notice some medical knowledge also in Greek literature, including Homer (8th century), but it was first Thucydides who wrote during the time of Hippocrates on Peloponnesian wars using or referring to term epidemic for disease that with weather and wind and air spreads among wider regions.

The term epidemic is derived from a word form attributed to Homer's Odyssey , which work later was taken by epidemiologists and epidemology's medical meaning for the Epidemics, as treatise made by Hippocrates. [6]

Before Hippocrates, epidemios, epidemeo, epidamos, and other variants had meanings similar to the current definitions of "indigenous" or "endemic". [6]

Thucydides' description of the Plague of Athens is considered one of the earliest written accounts of a disease epidemic using the exact term. [6] 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. [7] The term "epidemic" has become emotionally charged. [3]

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)." [2] 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 Concise Dictionary and Stedman's Medical Dictionary acknowledge this distinction. [3]

Causes

The Plague of Athens (c. 1652-1654) by Michiel Sweerts, illustrating the devastating epidemic that struck Athens in 430 BC, as described by the historian Thucydides Plague in an Ancient City LACMA AC1997.10.1 (1 of 2).jpg
The Plague of Athens (c. 1652–1654) by Michiel Sweerts, illustrating the 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: [2] :55

An epidemic disease is not required to be contagious, [3] [6] and the term has been applied to West Nile fever [3] and the obesity epidemic (e.g., by the World Health Organization [8] ), among others. [6]

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.

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. [9]  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. [10]

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. [2] :56

Propagated outbreak

In a propagated outbreak, the disease spreads person-to-person. Affected individuals may become independent reservoirs leading to further exposures. [2] :56

Many epidemics will have characteristics of both common source and propagated outbreaks (sometimes referred to 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. [2] :56–58

Transmission

Prevention and prevention preparations

Disease prevention preparations for an epidemic include having a disease indicators or rates 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. [13] [14]

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. [13] Still, despite the most extensive preparatory measures, a fast-spreading pandemic may easily exceed and overwhelm existing health-care resources. [11] Consequently, early and aggressive mitigation efforts, aimed at the so-called "epidemic curve flattening" need to be taken. [11] 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). [11]

See also

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<span class="mw-page-title-main">Pandemic</span> Global epidemic of infectious disease

A pandemic is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. A widespread endemic disease with a stable number of infected individuals is not a pandemic. Widespread endemic diseases with a stable number of infected individuals such as recurrences of seasonal influenza are generally excluded as they occur simultaneously in large regions of the globe rather than being spread worldwide.

<span class="mw-page-title-main">Zoonosis</span> Disease that can be transmitted from other species to humans

A zoonosis or zoonotic disease is an infectious disease of humans caused by a pathogen that can jump from a non-human to a human and vice versa.

<span class="mw-page-title-main">Infection</span> Invasion of an organisms body by pathogenic agents

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<span class="mw-page-title-main">Tularemia</span> Infectious disease caused by the bacterium Francisella tularensis

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<span class="mw-page-title-main">Disease outbreak</span> Sudden increase in occurrences of a disease

In epidemiology, an outbreak is a sudden increase in occurrences of a disease when cases are in excess of normal expectancy for the location or season. It may affect a small and localized group or impact upon thousands of people across an entire continent. The number of cases varies according to the disease-causing agent, and the size and type of previous and existing exposure to the agent. Outbreaks include many epidemics, which term is normally only for infectious diseases, as well as diseases with an environmental origin, such as a water or foodborne disease. They may affect a region in a country or a group of countries. Pandemics are near-global disease outbreaks when multiple and various countries around the Earth are soon infected.

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<span class="mw-page-title-main">Flu season</span> Recurring periods of influenza

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<span class="mw-page-title-main">Waterborne diseases</span> Diseases caused by pathogenic microorganisms transmitted in waters

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Globalization, the flow of information, goods, capital, and people across political and geographic boundaries, allows infectious diseases to rapidly spread around the world, while also allowing the alleviation of factors such as hunger and poverty, which are key determinants of global health. The spread of diseases across wide geographic scales has increased through history. Early diseases that spread from Asia to Europe were bubonic plague, influenza of various types, and similar infectious diseases.

<span class="mw-page-title-main">Isolation (health care)</span> Measure taken to prevent contagious diseases from being spread

In health care facilities, isolation represents one of several measures that can be taken to implement in infection control: the prevention of communicable diseases from being transmitted from a patient to other patients, health care workers, and visitors, or from outsiders to a particular patient. Various forms of isolation exist, in some of which contact procedures are modified, and others in which the patient is kept away from all other people. In a system devised, and periodically revised, by the U.S. Centers for Disease Control and Prevention (CDC), various levels of patient isolation comprise application of one or more formally described "precaution".

<span class="mw-page-title-main">Influenza</span> Infectious disease, often just "the flu"

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<span class="mw-page-title-main">Social distancing</span> Infection control technique by keeping a distance from each other

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<span class="mw-page-title-main">Airborne transmission</span> Disease transmission by airborne particles

Airborne transmission or aerosol transmission is transmission of an infectious disease through small particles suspended in the air. Infectious diseases capable of airborne transmission include many of considerable importance both in human and veterinary medicine. The relevant infectious agent may be viruses, bacteria, or fungi, and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, flushing toilets, or any activities which generate aerosol particles or droplets. This is the transmission of diseases via transmission of an infectious agent, and does not include diseases caused by air pollution.

Influenza prevention involves taking steps that one can use to decrease their chances of contracting flu viruses, such as the Pandemic H1N1/09 virus, responsible for the 2009 flu pandemic.

<span class="mw-page-title-main">Ira Longini</span> American biostatistician

Ira M. Longini is an American biostatistician and infectious disease epidemiologist.

In epidemiology, sporadic is a term used to refer to a disease which occurs only infrequently, haphazardly, irregularly or occasionally from time to time in a few isolated places with no discernible temporal or spatial pattern, as opposed to a recognizable epidemic or endemic pattern. The cases are so few and separated so widely in time and place that there exists little or no connection within them. They also do not show a recognizable common source of infection.

References

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  2. 1 2 3 4 5 6 7 Principles of Epidemiology (PDF) (Third ed.). Atlanta, Georgia: Centers for Disease Control and Prevention. 2012. Archived (PDF) from the original on 23 April 2019.
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  4. Further Report and Papers on Epidemic Influenza, 1889-92: With an Introduction by the Medical Officer of the Local Government Board. Great Britain. Local Government Boardр H.M. Stationery Office, 1893
  5. 1 2 3 A Brief History of Epidemic and Pestilential Diseases, Noah Webster, Hudson & Goodwin, 1799, p. 1-11
  6. 1 2 3 4 5 Martin PM, Martin-Granel E (June 2006). "2,500-year evolution of the term epidemic". Emerging Infectious Diseases. 12 (6): 976–980. doi:10.3201/eid1206.051263. PMC   3373038 . PMID   16707055.
  7. 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.
  8. Controlling the global obesity epidemic, the World Health Organization
  9. 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.
  10. Marcovitch H, ed. (2009). "Epidemic". Black's Medical Dictionary (42nd ed.). London: A&C Black. ISBN   978-1-4081-4564-7.
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  12. 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.
  13. 1 2 Gerson M (26 March 2015). "The next epidemic". The Washington Post .
  14. Gates B (April 2015). "The next epidemic--lessons from Ebola". The New England Journal of Medicine. 372 (15): 1381–1384. doi:10.1056/NEJMp1502918. PMID   25853741.

Further reading

External video
Nuvola apps kaboodle.svg Presentation by Brown on Influenza, March 5, 2019, C-SPAN