endemic / epidemic / pandemic
Always present in a place, a sharp outbreak, and an outbreak over a wide area.
Endemic means regularly found in a place or a population. Epidemic means a sharp outbreak in a community. Pandemic means an outbreak over a wide area, often many countries. Do not use epidemic for a disease that is simply always there.
Examples
Use endemic in the valley
Use an epidemic in the county
Use a pandemic across three continents
Avoid an epidemic in the valley (If the illness is always there.)