In epidemiology, what is the term for a persistent presence of a disease within a population?

The term for a persistent presence of a disease within a population is "endemic." When a disease is considered endemic, it means that its occurrence is stable and consistently observed in a specific geographic area or among a particular group of people. This can be thought of as the baseline level of disease expected in that population.

For example, certain diseases can be endemic to specific regions due to environmental factors, local behaviors, or other unique influences. One classic example is malaria in certain tropical regions where the conditions support the transmission cycle.

In contrast, an epidemic refers to a sudden increase in the number of cases of a disease above what is normally expected in that population, indicating a temporary surge rather than a stable presence. An outbreak is similar and often describes a more localized phenomenon. Surveillance, on the other hand, involves the systematic collection and analysis of data regarding disease occurrence to monitor health trends, rather than characterizing the presence of a disease itself.