What is the term for a sudden increase in the incidence of a disease?

The term for a sudden increase in the incidence of a disease is known as an outbreak. An outbreak refers to the occurrence of cases of a disease in a population, community, or region that is greater than what is normally expected. This term is often used in epidemiology to indicate that there is a higher-than-expected incidence of an illness, which can arise from various factors such as environmental changes, increased transmission among individuals, or the introduction of a new pathogen.

While terms like emergence, surge, and spike may seem relevant in different contexts, they don't precisely capture the established formal definition provided by public health authorities. Emergence typically refers to the first appearance of a disease or pathogen in an area, often linking to diseases that were previously unrecognized. Surge and spike suggest rapid increases but may not denote a specific threshold in incidence that classifies an outbreak. Thus, "outbreak" is the most accurate term to describe a significant escalation in disease incidence within a given timeframe or area.