Endemic
Etymology
From Greek endemos, "native, dwelling in a place," from en, "in," and demos, "the people." The idea is something at home in a population. A disease is endemic where it is always present at a steady, expected level. Ecologists borrow the word too: a species endemic to an island is found there and nowhere else.
adjective · /en-DEM-ik/
Regularly found in, and characteristic of, a particular place or population.
What it names
The difference between a disease that flares up and one that is simply a constant feature of a region — a distinction that changes how you plan.
Example
Malaria remains endemic in parts of the region, a steady background rather than a sudden surge.
Related idea
An epidemic is a sharp rise above the usual level; endemic is the usual level itself.