Endemic (epidemiology)
In epidemiology, an infection is said to be endemic in a specific population or 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, chickenpox is endemic (steady state) in the United Kingdom, but malaria is not. Every year, there are a few cases of malaria reported in the UK, but these do not lead to sustained transmission in the population due to the lack of a suitable 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.
Misuse[edit]
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.
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]
