Endemic (epidemiology)

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Endemicity
)

Human alphaherpesvirus 3 virion − a herpesvirus known to infect humans. It causes chickenpox (varicella), a disease most commonly affecting children, teens, and young adults, and shingles (herpes zoster) in adults.

In

populated place when that infection is constantly present, or maintained at a baseline level, without extra infections being brought into the group as a result of travel or similar means.[1] The term describes the distribution (spread) of an infectious disease among a group of people or within a populated area.[2] An endemic disease always has a steady, predictable number of people getting sick, but that number can be high (hyperendemic) or low (hypoendemic), and the disease can be severe or mild.[3][4] Also, a disease that is usually endemic can become epidemic.[3]

For example,

vector (mosquitoes of the genus Anopheles
). Consequently, the number of people infected by malaria in the UK is too variable to be called endemic. However, the number of people who get chickenpox in the UK varies little from year to year, so chickenpox is considered endemic in the UK.

Mathematical determination

For an infection that relies on person-to-person transmission, to be endemic, each person who becomes infected with the disease must pass it on to one other person on average. Assuming a completely susceptible population, that means that the

transmitted
being susceptible to it, effectively discounting the immune sector of the population. So, for a disease to be in an endemic steady state or endemic equilibrium, it holds that

In this way, the infection neither dies out nor does the number of infected people increase

If a disease is in an endemic steady state in a population, the relation above allows us to estimate the

mathematical model for the epidemic. Based on the reproduction number, we can define the epidemic waves, such as the first wave, second wave, etc. for COVID-19 in different regions and countries.[6]

Misuse

While it might be common to say that

AIDS is endemic in some countries, meaning that it is regularly found in an area, this is a use of the word in its etymological, rather than epidemiological or ecological, form.[citation needed
]

Some in the public wrongly assume that endemic COVID-19 means the disease severity would necessarily be mild.[3] Endemic COVID-19 could be mild if previously acquired immunity reduces the risk of death and disability during future infections,[7] but in itself endemicity only means that there will be a steady, predictable number of sick people.[3][4]

Related terms

Categories of endemic diseases

Holoendemic
An endemic disease with an extremely high rate of infection,
immunity.[9]
Hyperendemic
An endemic disease with a high rate of infection,[8] especially one affecting people of all ages equally.[9]
Mesoendemic
An endemic disease with a moderate rate of infection.[8] This term is often used to describe the prevalence of malaria in a local area, with 10 to 50% of children showing evidence of prior infection being considered a moderate level for that disease.[8][10]
Hypoendemic
An endemic disease with a low rate of infection.[8][9] Typhoid fever is a hypoendemic disease in the US.[11]

Categories for non-endemic diseases

Sporadic
A disease that appears occasionally, but, unlike endemic disease, is not always present at a steady and predictable level.[12]
Outbreak
An epidemic, especially one affecting a very small area, such as the people in one town or attending a single event.
unvaccinated people.[3]
Epidemic
A new disease that is spreading or a previously endemic disease whose infection rate is increasing significantly.
Seasonal flu frequently appears as an epidemic.[8]
Pandemic
An epidemic affecting a very large part of the world, generally multiple countries or multiple continents.[8] Seasonal flu is sometimes a global pandemic.[8]

Examples

This is a short, incomplete list of some infections that are usually considered endemic:

Smallpox was an endemic disease until it was eradicated through vaccination.[13]

Etymology

The word endemic comes from the Greek: ἐν, en, "in, within" and δῆμος, demos, "people".[citation needed]

See also

References

  1. ^ "Principles of Epidemiology in Public Health Practice, Third Edition An Introduction to Applied Epidemiology and Biostatistics". Centers for Disease Control and Prevention. Retrieved 19 April 2018.
  2. . Terms used to describe distribution include: Endemic: a condition that is generally present in a group or area, such as a cold
  3. ^ .
  4. ^ .
  5. , retrieved 28 February 2023
  6. .
  7. .
  8. ^ .
  9. ^ .
  10. .
  11. ^ .
  12. .
  13. ^ . Yes, common colds are endemic. So are Lassa fever, malaria and polio. So was smallpox, until vaccines stamped it out. [...] learning to live with endemic rotavirus, hepatitis C or measles.

External links

  • The dictionary definition of endemic at Wiktionary