In the medical sciences, the term endemic refers to an infectious disease that survives in a population without input from some external source.
Endemic diseases are always present in an affected population, usually at relatively low, but constant, levels. For example, malaria is endemic to sub-Saharan Africa, where it is so common that humans have evolved a genetic factor (the sickle-cell trait) that protects against the disease. Endemic diseases are transmitted from person to person, either directly or by means of a vector, such as a mosquito. As long as there are enough humans with a disease to continue passing it on in a region, or as long as a vector is present in adequate numbers, the disease will persist—it will be endemic—in the population. The likelihood of a disease becoming endemic in a region is obviously a function of the density of human population in the area. The denser the population, the greater the number of interpersonal contacts, and the greater the likelihood the disease will be spread from person to person. Living conditions are also a factor, since unsanitary conditions promote the survival and breeding of vectors and the maintenance of an infectious disease.
The term endemic is also used to describe noninfective diseases and health conditions. For example, some people have described obesity as endemic in certain parts of the developed world, such as the United States. That term is appropriate because the factors that lead to obesity, such as an abundance of food and a relative lack of physical exercise, are now fundamental parts of American life; obesity is likely to continue as an endemic health problem unless significant efforts are made to either reduce or eliminate the contributing factors or to make individuals aware of their role in producing an unhealthy lifestyle.
Some examples of endemic diseases and their incidence (number of new cases annually) or prevalence (total number of present cases) are as follows:
An example of the success that public health programs have had with endemic diseases is tuberculosis. At one time, the disease was endemic in many developed countries, especially among the urban poor. During the nineteenth and early twentieth centuries, the disease was responsible for one out of four deaths in England and one in six deaths in France. When the cause of the disease was finally determined in 1882 by Robert Koch, public health workers gained the knowledge they needed to begin making inroads against the disease. As a consequence, the rate of tuberculosis in developed nations dropped dramatically in the twentieth and twenty-first centuries, although the disease is still endemic and widespread in most parts of the developing world.
See also Communicable diseases .
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World Health Organization, Avenue Appia 20, 1211 Geneva 27, Switzerland, 2241 791 21 11, Fax: 2241 791 31 11, firstname.lastname@example.org, http://www.who.int .
David E. Newton, EdD