Epidemic
Rapid spread of disease above normally expected levels.
An epidemic is the rapid spread of disease to a large number of hosts in a given population within a short period of time. The term derives from Greek ἐπί epi 'upon or above' and δῆμος demos 'people'. The word form is attributed to Homer's *Odyssey*, but its medical meaning comes from the *Epidemics*, a treatise by Hippocrates. Before Hippocrates, related terms had meanings similar to "indigenous" or "endemic." Thucydides' description of the Plague of Athens is considered one of the earliest accounts of a disease epidemic. By the early 17th century, "endemic" referred to a common sickness, while "epidemic" described a disease happening in a region at a certain time, producing the same sickness in all sorts of people. The term is often applied to diseases in non-human animals, though "epizootic" is technically preferable.
The United States Centers for Disease Control and Prevention defines epidemic broadly as an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area. The term "outbreak" can also apply but is usually restricted to smaller events. Any sudden increase in disease prevalence may be termed an epidemic, including contagious diseases like influenza, vector-borne diseases like malaria, water-borne diseases like cholera, and sexually transmitted diseases like HIV/AIDS. The term can also be used for non-communicable health issues such as obesity. For example, in meningococcal infections, an attack rate exceeding 15 cases per 100,000 people for two consecutive weeks is considered an epidemic. An epidemic may be restricted to one location; if it spreads to other countries or continents and affects a substantial number of people, it may be termed a pandemic. 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 above this baseline. A few cases of a very rare disease may be classified as an epidemic, while many cases of a common disease like the common cold would not. Epidemics can cause enormous damage through financial and economic losses in addition to impaired health and loss of life.
- Etymology
- Greek ἐπί (epi) 'upon or above' and δῆμος (demos) 'people'
- First medical use
- Attributed to Hippocrates' treatise Epidemics
- Defining organization
- United States Centers for Disease Control and Prevention
- Related term
- Pandemic (when spread to other countries or continents affecting a substantial number of people)
Lore & Background
The term epidemic derives from a word form attributed to Homer's Odyssey, which later took its medical meaning from the Epidemics, a treatise by Hippocrates. Before Hippocrates, variants had meanings similar to 'indigenous' or 'endemic'. Thucydides' description 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 contrasting conditions of population-level disease, with the epidemic described as 'hapning in some region, or countrey, at a certaine time, ....... producing in all sorts of people, one and the same kind of sicknesse'.
Reader's Guide
Epidemics are generally caused by several factors including a change in the ecology of the host population, a genetic change in the pathogen reservoir, or the introduction of an emerging pathogen. An epidemic occurs when host immunity to an established or novel pathogen is suddenly reduced below that found in the endemic equilibrium and the transmission threshold is exceeded. 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. The term can also be used for non-communicable health issues such as obesity. The United States Centers for Disease Control and Prevention defines epidemic broadly as 'an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area.' The term 'outbreak' can also apply, but is usually restricted to smaller events.
Did You Know?
- The term epidemic derives from a word form attributed to Homer's Odyssey.
- Thucydides' description of the Plague of Athens is considered one of the earliest accounts of a disease epidemic.
- The United States Centers for Disease Control and Prevention defines epidemic as 'an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area.'
- The term can also be used for non-communicable health issues such as obesity.
More in Infectious Diseases 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record