epidemic

(-ĭ-kəl)
adj.

1. Spreading rapidly and extensively by infection and affecting many individuals in an area or a population at the same time: an epidemic outbreak of influenza.
2. Widely prevalent: epidemic discontent.

n.

1. An outbreak of a contagious disease that spreads rapidly and widely.
2. A rapid spread, growth, or development: an unemployment epidemic.

[French épidémique, from épidémie, an epidemic, from Old French espydymie, from Medieval Latin epidēmia, from Greek epidēmiā, prevalence of an epidemic disease, from epidēmos, prevalent : epi-, epi- + dēmos, people.]

epidemically ep'i·dem'i·cal·ly adv.

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 also Epidemiology; Infectious disease; Public health.

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Epidemics come with wings and slowly limp away (from a French proverb).

The word ‘epidemic’ has an emotional ring to it. This is probably the reason why it is often used wrongly when, strictly speaking, other epidemiological terms such as pandemics or outbreaks should be employed to enumerate disease. An epidemic (from the Greek: epi upon; demos, people) is usually defined as a large-scale, temporary increase in the occurrence of a disease in a community or region which is clearly in excess of normal expectancy, whereas a pandemic (pan, all) is the occurrence of a disease which is clearly in excess of normal expectancy and is spread over a whole geographical area, usually crossing national boundaries.

At the other end of the scale are outbreaks and sporadic cases. An outbreak may be a household or a general outbreak. A household outbreak involves two or more persons resident in the same household whose illness is associated in time but not apparently connected with any other case or outbreak. A general outbreak involves two or more persons who are not confined to one household but are associated in time and location. A sporadic case refers to a person whose illness is not apparently connected with similar illnesses in any other persons.

A disease or infectious agent is said to be endemic when it is constantly present within a given location or population group.

Although the term ‘epidemic’ is used widely to describe clusters of disease in general, and even in a non-medical sense (e.g. an epidemic of road rage), it has traditionally been used when infection strikes a population. This often occurs when there is crowding together of humans (or, for that matter, animals, fish, or birds), as this provides the necessary conditions to allow microorganisms to multiply and spread. When humans led nomadic lives there was often less chance for epidemics to occur; the main opportunities came when large numbers gathered for such things as pilgrimages or wars — and when subsequently the group dispersed the chances of carrying the infection elsewhere were multiplied.

The threat of epidemics in overcrowded and difficult conditions is particularly well illustrated in military history; on many occasions the germ has been as important as the sword or gun in determining the outcome of a campaign. The Spanish conquest of Mexico owes much of its success to an epidemic of smallpox that destroyed about half of the Aztec population. The typhoid bacillus caused severe effects during both the American Civil War (1861-5) and the Boer War (1899-1902). The use of typhoid vaccine in the latter years of World War I meant that the main impact of typhoid in this war subsided after 1916. Similarly, typhus was rife in the Civil War in Britain (1642-9), when both the Parliamentary and Royalist armies were affected.

There are three main patterns of epidemic, determined by the mode of transmission of the microorganism.

Firstly, the explosive epidemic. This is characterized by the occurrence of many cases in a relatively short period; there is a sharp rise and fall in the number of infected persons, since the usual cause of such an event is a common source of infection. This type of epidemic is thus also frequently termed a common source epidemic or a point source epidemic. This pattern of infection often occurs when water or food becomes contaminated, although other vehicles of infection can also be responsible.

Secondly, person-to-person spread. These epidemics usually have a more protracted course, taking longer than explosive epidemics to build up and subside. An infective agent may be passed from person to person by a variety of routes (e.g. respiratory or gastrointestinal). Diseases such as influenza or chickenpox often follow this pattern.

Thirdly — a combination of the two — an explosive epidemic with subsequent person-to-person spread. This pattern is apparent when there is contamination of a common water or food source and the initial cases then infect their contacts. Although this type of epidemic starts in the same way as an explosive incident, there is a slower decline.

The importance of keen observation and recording of epidemics in order to deduce the likely cause has been demonstrated on many occasions, and may be considerably in advance of microbiological proof. In 1849, 34 years before the identification of Vibrio cholerae by Robert Koch (1843-1910), John Snow (1813-58), a London physician, proved by epidemiological observation that cholera is mainly spread by drinking infected water, rather than through the air in the form of a miasma as was commonly thought at the time. Similarly, William Budd (1811-80), a general practitioner in Devon, showed in 1873 how typhoid was caused, even though it was not until 1885 that Salmonella typhi was first isolated in the laboratory. More recently, William Pickles (1885-1969), a general practitioner in Wensleydale, Yorkshire, was able to elucidate many of the epidemiological characteristics of viral hepatitis well before microbiological advances were to confirm his observations.

— Daniel Reid

Bibliography

• Pickles W. N. (1939). Epidemiology in country practice. Wright, Bristol. (Re-issued in 1972 by the Devonshire Press, Torquay.)
• Tyrrel, D. A. J. (1982). The abolition of infection. Hope or illusion? Rock Carling Fellowship Lecture. Nuffield Provincial Hospitals Trust, London

See also infectious diseases; pandemics.

noun

A sudden increase in something, as the occurrence of a disease: outbreak, plague, rash². See increase/decrease.

adj

Definition: widespread
Antonyms: limited

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adj

Spreading rapidly and widely among many individuals in a single location or region; illnesses labeled epidemic are those that occur beyond normal expectations and are usually traceable to a single source.

An epidemic is an occurrence of cases of a disease in excess of usual expectations for a particular population. An outbreak of influenza that affects thousands of people in a month in a nation and a half dozen cases of a rare form of liver cancer affecting industrial workers in a chemical plant over a period of several years are both examples of epidemics. Another kind of epidemic can be seen in the sharp rise in the prevalence of cigarette smoking throughout the twentieth century—first among males and then females—and of smoking-related respiratory system cancers. The surging death rate from coronary heart disease among men in many industrial nations in the middle third of the twentieth century may also be described as an epidemic.

A pandemic is a worldwide epidemic that kills or incapacitates huge numbers in many countries. Outbreaks of influenza in 1919 and HIV/AIDS (human immunodeficiency virus/acquired immunodeficiency syndrome) since the 1980s are both examples of pandemics. Conditions that are constantly present in a community are called "endemic;" examples include malaria in some tropical regions, and goiter due to deficiency of iodine in the soil of certain areas.

A single case of a rare and dangerous contagious disease that has never occurred before or has long been absent from a community represents a potential epidemic, as does a small cluster of cases of a disease such as typhoid in an urban community with good sanitation. Infectious pathogens (bacteria and viruses) cause most epidemics, while some are caused by a toxic industrial process or a toxic substance in food or water. A toxin in cooking oil in Spain in 1981 poisoned several thousand people, damaging their kidneys, liver, lungs, and nervous system and causing many deaths and widespread chronic disability. The precise nature of this contaminant was never established. In 1976, members of the American Legion who had attended a convention in Philadelphia began to fall ill and die of an unusual form of pneumonia, mostly after they returned to their homes elsewhere in the United States. Investigations by the Centers for Disease Control revealed this to be an epidemic of what is now called Legionnaire's disease, which is caused by a previously unknown microorganism that can be disseminated via the moist air in poorly maintained air-conditioning systems.

Charles Mackay, in his classic work Extraordinary Popular Delusions and the Madness of Crowds, described what is known as a behavioral epidemic. This phenomenon can be seen in the reactions of impressionable teenagers at a rock concert—and in a more sinister form in movements such as Nazism, when an entire nation is gripped by destructive fanaticism. The huge increase in traffic-related death and injury rates during the twentieth century, which has continued into the twenty-first century, is a behavioral epidemic associated with addiction to high-speed automobiles (the phenomenon called "road rage" is a psychopathic variation of this epidemic).

Human history has been punctuated frequently by epidemics, and occasionally by pandemics, that have shaped the rise and fall of civilizations and the victories and defeats of warring armies. The outcome of the Peloponnesian War (431–404 B.C.E.) between Athens and Sparta—and the future course of Western civilization—might have been very different had it not been for the epidemic that decimated the Athenians at the beginning of the war. Although the historian Thucydides, who had the disease himself, described its symptoms and signs in detail, modern epidemiologists cannot identify it.

Epidemic sweating sickness recurred several times in medieval Europe, but it has vanished since. The Black Death, or plague, that struck Europe in 1347 killed between one-third and one-half of the people in many cities and towns, arresting the advance of civilization for several generations. Some epidemic diseases, such as the plague, smallpox, typhus, and influenza, have persisted throughout recorded history. Smallpox was eradicated worldwide by 1980. Cholera appeared along the world's major trade routes in several devastating epidemics beginning in the eighteenth century, and it still causes massive epidemics, most recently in South America in early 1990s.

In the final quarter of the twentieth century over thirty new infectious pathogens were identified. Many of these have caused deadly localized epidemics (e.g. Ebola virus, hantavirus, and other viral hemorrhagic fevers), and some have spread worldwide—HIV/AIDS being the foremost among these. Since its first recognition in 1981, HIV has affected almost 40 million people and killed over 10 million, making it the most lethal and dangerous pandemic since the Black Death. Other new and emerging infections that have caused epidemics include Legionnaire's disease, Lyme disease, newly identified hepatitis viruses spread in epidemic form through contaminated blood and blood products used in transfusion services, and several bacterial and viral diseases affecting the gastrointestinal tract.

An epidemic is a public health emergency requiring immediate investigation. The steps in investigating an epidemic are as follows:

1. Confirm the diagnosis.
2. Verify that the number of cases is outside normal expectations.
3. Define features in common among the cases (including inapparent cases).
4. Distinguish cases from members of the community who are not affected.
5. Compare the exposure history of the cases with a sample of noncases.
6. Conduct appropriate laboratory tests for pathogenic organisms.
7. Review environment and social conditions.
8. Arrange, classify, and analyze the data.
9. Plot graphs of time trends and the number of cases; create maps of the distribution of cases.
10. Report findings to the public health authorities for action to control the epidemic.

In the investigation it is important to consider the host (the affected individuals), the agent (the cause of the condition), and the environment. Physical, biological, social, behavioral, and cultural factors must also be considered. Investigating an epidemic can be as exciting as detective fiction, and such investigations (both real and fictional) have yielded many best-selling books and movies. The Epidemic Intelligence Service (EIS) of the U.S. Centers for Disease Control and Prevention has an illustrious record of successfully investigating and controlling epidemics, including some great public health importance. The first investigations of HIV/AIDS were done mainly by EIS staff and close collaborators in New York and Los Angeles.

Several kinds of epidemics can be distinguished. A point-source epidemic is one in which a group of people all fall ill as a result of a single exposure, typically to an agent in food they have all consumed. An example would be an outbreak of acute food poisoning due to staphylococcal enterotoxin. A common-vehicle epidemic is due to an agent that is spread on an ongoing basis in a "vehicle" such as food, water, or air. Food-borne common-vehicle epidemics usually cause gastrointestinal disease, and are sometimes perpetuated by a carrier who is a foodhandler. Waterborne epidemics include typhoid, giardia, viral hepatitis A, and many others. The best known airborne common vehicle epidemic is Legionnaire's disease. Notorious blood-borne common-vehicle epidemics have occurred since the 1980s in many countries after the blood supply became infected with HIV or Hepatitis C virus. Vector-borne epidemics are spread by insect vectors and include viruses such as dengue and viral encephalitis, which are transmitted by mosquitoes.

Control and prevention of an epidemic requires elimination of the source, or, if this is not feasible, precautions to prevent transmissions from the source to susceptible human hosts. The same approach applies when the agent causing the epidemic is not an infectious pathogen but a chemical poison or an allergen; and it can even be applied, with suitable adjustments, to control of behavioral epidemics like mass hysteria and schoolyard vandalism.

Viewed from the perspective of evolutionary biology, epidemics will forever be a part of human-kind's experience. The interaction of human hosts with infectious pathogenic organisms is everchanging, in complex ecosystems that are also ever-changing, often as a result of human activity.

(SEE ALSO: Adherence or Compliance Behavior; Black Death; Blood-Borne Diseases; Centers for Disease Control and Prevention; Classification of Disease; Common Vehicle Spread; Communicable Disease Control; Contagion; Emerging Infectious Diseases; Epidemic Intelligence Service; Epidemiologic Surveillance; Epidemic Theory: Herd Immunity; Epidemiology; Food-Borne Diseases; HIV/AIDS; Notifiable Diseases; Vector-Borne Diseases; Waterborne Diseases; and articles on specified diseases mentioned herein)

Bibliography

Gregg, M. B. (1996). Field Epidemiology. New York: Oxford University Press.

Mackay, C. (1841). Extraordinary Popular Delusions and the Madness of Crowds. Reprint. Boston: L. C. Page & Company, 1932.

Roueché, B. (1954). Eleven Blue Men and Other Annals of Medical Detection. Boston: Little, Brown, & Co.

— JOHN M. LAST

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A contagious disease that spreads rapidly and widely among the population in an area. Immunization and quarantine are two of the methods used to control an epidemic.

A level of disease occurrence in an animal population which is significantly greater than usual; only occasionally present in the population, widely diffused and rapidly spreading. The disease is clustered in space and time. The word has common usage in veterinary science in preference to the more accurate, epizootic.

• common source e. — see point epidemic (below).
• e. curve — see epidemic curve.
• e. diarrhea of infant mice — see murine epizootic diarrhea.
• e. hyperthermia — poisoning by Neotyphodium (Acremonium) coenophialum; called also fescue summer toxicosis.
• multiple event e. — when the epidemic begins at about the same time in a number of places, e.g. when a poisoned batch of feed is supplied to a number of farms.
• point e. — when the epidemic begins at one central point, with a large number of animals coming in contact with the source over a short time; a very rapid form of spread with a number of cases presenting with the same stage of the disease at the one time, indicating the single source of the pathogen.
• propagated e., propagative e., propagating e. — outbreaks in which the disease propagates in one or more initial cases and then spreads to others, a relatively slow method of spread.
• e. tremor — see avian encephalomyelitis.
• e. typhus — see rickettsia prowazeki.

IN BRIEF: The rapid spreading of a disease to many people at the same time.

Every fall, the medical community worries about the possibility of a flu epidemic.

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - epidemi, epidemisk sygdom
adj. - epidemisk

Nederlands (Dutch)
epidemie, epidemisch

Français (French)
n. - épidémie
adj. - épidémique

Deutsch (German)
n. - Epidemie
adj. - epidemisch

Ελληνική (Greek)
n. - (ιατρ., μτφ.) επιδημία
adj. - επιδημικός

Italiano (Italian)
epidemia, epidemico

Português (Portuguese)
n. - epidemia (f) (Med.)
adj. - epidêmico (Med.)

Русский (Russian)
эпидемия, вспышка, эпидемический, повальный

Español (Spanish)
n. - epidemia, peste, plaga
adj. - epidémico, epidemial

Svenska (Swedish)
n. - epidemi
adj. - epidemisk

中文（简体）(Chinese (Simplified))
传染病, 流行病, 流行的, 传染性的

中文（繁體）(Chinese (Traditional))
n. - 傳染病, 流行病
adj. - 流行的, 傳染性的

한국어 (Korean)
n. - 전염병
adj. - 유행성의

日本語 (Japanese)
adj. - 流行性の, 流行している
n. - 伝染病, 流行

العربيه (Arabic)
‏(الاسم) وباء (صفه) وبائي‏

עברית (Hebrew)
n. - ‮מגפה, אפידמיה‬
adj. - ‮מידבקת (מגפה), מתפשט מהר, מגיפתי‬

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