What Does “Endemic” Mean?

Endemic is a word often used to describe a disease, but what does it mean? A disease is said to be endemic when a large or significant number of cases are constantly encountered in a given area or population group. This is not to be confused with an “epidemic,” which is a widespread outbreak of a disease that can occur at any time and affects a large number of people who live in close proximity, or in close succession.

For example, endemic can be used to describe the occurrence of various forms of dysentery and botulism in developing and third-world countries. In these areas where sanitary levels may be poor and water is not well treated, these conditions are typical and rampant.

Endemic is a term that has become a little more fluid with the modern age, however, since people are globally more mobile and can carry and transmit disease that were previously endemic to specific areas all over the world.

Various factors can contribute to maintaining a disease at the endemic level. One way this is accomplished is that the disease has not been eradicated. While polio rarely happens in the United States, the disease has not been completely irradiated. The same can be said for a disease like Rickets, that used to be very common (endemic) in the United States, but now occurs elsewhere in the world and rarely among individuals who are native to the U.S. Secondly, there has to be a susceptible grouping within a population of the sufficient magnitude to keep the disease process active. Diseases are more likely to remain endemic and “alive” in urban areas where the population concentration is more dense.

Here is where the terms “endemic” and “epidemic” can become confusing. An increased attack or outbreak of a disease that has been considered endemic in a particular area can become an epidemic in these areas where the disease has been dormant or a minor concern for a period of time. This may be due to a change in conditions that make things more favorable for the disease, such a new or modified strain, a change in climate, or a combination of factors that make an outbreak of a disease spread quickly to epidemic status.

Unusual instances of crowding seem to increase the chances for epidemics, such as during war, natural disasters or other traumatic and catastrophic events. An endemic disease or condition can become an epidemic in institutions, refugee encampments, evacuation sites and other occurrences of intensifying population and exposing people to a variety of bacteria and organisms that may cause disease.