Which feature best identifies an emerging disease?

• A. Identified for the first time in the last 10 years
• B. Expanding host range
• C. Increasing in incidence and severity
• D. Recently identified in a new location

Answer: (C)

An emerging disease is best identified when there is a sustained increase in the number of cases and in how severe the disease is. This combination shows that the pathogen is not only spreading within a population but also causing more serious outcomes, indicating a real shift in its impact and behavior.

Other signals can be important but are less definitive on their own. Being identified for the first time in a given period can reflect improved detection rather than true growth in transmission. Expanding host range signals new potential for spread across species, but doesn’t by itself prove an overall rise in incidence or severity in the human or animal population. Detection in a new location points to geographic spread, which is important, but may arise from surveillance changes rather than a true rise in burden.

So, the strongest indicator is increasing incidence with greater severity, signaling actual expansion of the disease in the population.