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outbreak of disease that affects a much greater number of people than is usual for the locality or that spreads to regions where it is ordinarily not present. A disease that tends to be restricted to a particular region (endemic disease) can become epidemic if nonimmune persons are present in large numbers (as in time of war or during pilgrimages), if the infectious agent is more virulent than usual, or if distribution of the disease is more easily effected. Choleracholera
or Asiatic cholera,
acute infectious disease caused by strains of the bacterium Vibrio cholerae that have been infected by bacteriophages. The bacteria, which are found in fecal-contaminated food and water and in raw or undercooked seafood, produce a
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 and plagueplague,
any contagious, malignant, epidemic disease, in particular the bubonic plague and the black plague (or Black Death), both forms of the same infection. These acute febrile diseases are caused by Yersinia pestis (Pasteurella pestis
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, endemic in parts of Asia, can become epidemic under the above conditions, as can dysenterydysentery
, inflammation of the intestine characterized by the frequent passage of feces, usually with blood and mucus. The two most common causes of dysentery are infection with a bacillus (see bacteria) of the Shigella group, and infestation by an ameba,
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 and many other infections. Epidemics, often now simply called "outbreaks" by epidemiologists, may also be caused by new disease agents in the human population, such as the Ebola virusEbola virus
, a virus of the genus Ebolavirus, which belongs to a family (Filoviridae) of RNA viruses that cause hemorrhagic fevers. The viruses, named for a river in Congo (Kinshasa) near where the first species was first identified in 1976, emerged from the rain
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. A worldwide epidemic is known as a pandemic, e.g., the influenzainfluenza
or flu,
acute, highly contagious disease caused by a RNA virus (family Orthomyxoviridae); formerly known as the grippe. There are three types of the virus, designated A, B, and C, but only types A and B cause more serious contagious infections.
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 pandemic of 1918 or the AIDSAIDS
or acquired immunodeficiency syndrome,
fatal disease caused by a rapidly mutating retrovirus that attacks the immune system and leaves the victim vulnerable to infections, malignancies, and neurological disorders. It was first recognized as a disease in 1981.
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 pandemic beginning in the 1980s. Officially, the World Health Organization considers any disease outbreak that is spreading unchecked in two different regions of the worlds to be a pandemic; classification as a pandemic is not an indicator of the severity of a disease. A disease is said to be sporadic when only a few cases occur here and there in a given region. Epidemic disease is controlled by various measures, depending on whether transmission is through respiratory droplets, food and water contaminated with intestinal wastes, insect vectors, or other means. The Centers for Disease Control and PreventionCenters for Disease Control and Prevention
(CDC), agency of the U.S. Public Health Service since 1973, with headquarters in Atlanta; it was established in 1946 as the Communicable Disease Center.
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 tracks epidemics in the United States.

See also epdemiologyepidemiology,
field of medicine concerned with the study of epidemics, outbreaks of disease that affect large numbers of people. Epidemiologists, using sophisticated statistical analyses, field investigations, and complex laboratory techniques, investigate the cause of a
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The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/


The occurrence of cases of disease in excess of what is usually expected for a given period of time. Epidemics are commonly thought to involve outbreaks of acute infectious disease, such as measles, polio, or streptococcal sore throat. More recently, other types of health-related events such as homicide, drownings, and even hysteria have been considered to occur as “epidemics.”

Confusion sometimes arises because of overlap between the terms epidemic, outbreak, and cluster. Although they are closely related, epidemic may be used to suggest problems that are geographically widespread, while outbreak and cluster are reserved for problems that involve smaller numbers of people or are more sharply defined in terms of the area of occurrence. For example, an epidemic of influenza could involve an entire state or region, whereas an outbreak of gastroenteritis might be restricted to a nursing home, school, or day-care center. The term cluster may be used to refer to noncommunicable disease states.

In contrast to epidemics, endemic problems are distinguished by their consistently high levels over a long period of time. Lung cancer in males has been endemic in the United States, whereas the surge of lung cancer cases in women in the United States represents an epidemic problem that has resulted from increase in cigarette smoking among women in general. A pandemic is closely related to an epidemic, but it is a problem that has spread over a considerably larger geographic area; influenza pandemics are often global.

Disease and epidemics occur as a result of the interaction of three factors, agent, host, and environment. Agents cause the disease, hosts are susceptible to it, and environmental conditions permit host exposure to the agent. An understanding of the interaction between agent, host, and environment is crucial for the selection of the best approach to prevent or control the continuing spread of an epidemic.

For infectious diseases, epidemics can occur when large numbers of susceptible persons are exposed to infectious agents in settings or under circumstances that permit the spread of the agent. Spread of an infectious disease depends primarily on the chain of transmission of an agent: a source of the agent, a route of exit from the host, a suitable mode of transmission between the susceptible host and the source, and a route of entry into another susceptible host. Modes of spread may involve direct physical contact between the infected host and the new host, or airborne spread, such as coughing or sneezing. Indirect transmission takes place through vehicles such as contaminated water, food, or intravenous fluids; inanimate objects such as bedding, clothes, or surgical instruments; or a biological vector such as a mosquito or flea. See Epidemiology, Infectious disease

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



the spread of an infectious human disease that substantially exceeds the ordinary (sporadic) sick rate in a particular area.

Epidemics are caused by social and biological factors. Their basis is the epidemic process, that is, the continuous transmission of the causative agent of the infection and an unbroken chain of successively developing and interdependent infectious conditions (disease, bacteria carrier state) in a group of people. The spread of a disease is sometimes pandemic in nature; in other words, under certain natural or sociohygienic conditions, a comparatively high incidence of a disease may be recorded in a particular area over a long period of time.

The origin and course of an epidemic are influenced both by processes occurring under natural conditions (natural focality, epizootic) and, especially, by social factors (public utilities, living conditions, quality of health care). Depending on the nature of the disease, the main routes by which an infection spreads during an epidemic may be water and food, as in dysentery and typhoid; airborne droplets, as in influenza; and person-to-person transmission, as in malaria and typhus. Often the causative agent is transmitted by several means.

The study of epidemics and methods of controlling them is called epidemiology.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A sudden increase in the incidence rate of a disease to a value above normal, affecting large numbers of people and spread over a wide area.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


1. (esp of a disease) attacking or affecting many persons simultaneously in a community or area
2. a widespread occurrence of a disease
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
This was a particular danger, indeed an 'Epidemical disease', when it came to 'the Authors of this age', for they were all 'engaged in parties' to such an extent 'that their writings will rather appear pleadings than reports'.
Researchers at Kent State University Ashtabula and the Infection Control Practitioners at ACMC have established a collaborative project to investigate and characterize the epidemical changes in MRSA incidence among the younger population in Ashtabula County.
This constancy remains, regardless of the physician, institution, time, place, or type of epidemical disease, including diseases carrying a very high mortality rate, such as cholera, smallpox, diphtheria, typhoid fever, yellow fever, and pneumonia.
This technique was used in a PhD thesis studying social and epidemical impact on patients treated by a Medicinal Plants Program at the University of Chapingo (Mexico).
This excellent book derives from Thomas Keymer and Peter Sabor's previous joint work--The 'Pamela' Controvery: Criticisms and Adaptations of Samuel Richardson's 'Pamela', 1740-1750, 6 vols (London: Pickering & Chatto, 2001), which provided headnotes to the facsimiles of the many pamphlets, parodies, plays, verses, illustrations, and other printed matter generated by the 'Epidemical Phrenzy' caused by Richardson's best-seller.
For example, the assertion that Burton theorizes the collective melancholy of bodies politic by drawing upon the occult concept of sympathy (as formulated by Fracastoro) is purely speculative and unsupported by the text of the Anatomy, which offers no such explanation but simply refers to Botero and states that the melancholy of such states can be "easily perceave[d] by their particular Symptomes." However, the general emphasis on the collective, epidemical status of melancholy for Burton is undoubtedly correct.
The success of the PNT demonstrates that it is possible, even in a developing country such as Costa Rica, to implement preventive actions and to address effectively the enormous challenges that the new epidemical profile imposes.
All the arguments I can use to induce you to take notice of this thing of nothing, is, that it had the luck to tumble last of all in the Epidemical ruine of the Scene; and now limps hither with a wooden Leg, to beg an Alms at your hands [...] since the Times conspire to make us all Beggars, let us make ourselves merry.
In the early part of the present century there was an epidemical rage in Europe for this species of compacts, from which the politicians of the times fondly hoped for benefits which were never realized.
The board was also given wide discretion to make such rules and regulations relative to the operation of quarantine as it deemed fit, in any situation where an "epidemical" disease had established itself in the city, or "upon a probable approach" of such a disease.