Which term describes the total number of existing cases at a given time?

• A. Incidence
• B. Prevalence
• C. Attack rate
• D. Mortality rate

Answer: (B)

Prevalence describes how many people in a population have a condition at a given time, capturing the overall burden. It includes those who already have the disease as well as new cases that still exist at that moment. This is different from incidence, which counts only new cases over a defined period. Attack rate is a type of incidence used during outbreaks to estimate risk among those exposed, and mortality rate refers to deaths in the population over time. So describing the total number of existing cases at a given time aligns with prevalence, which is often expressed as a proportion of the population (point or period prevalence). For example, in a city of 100,000, if 1,500 people have diabetes on a specific date, the point prevalence is 1,500/100,000 = 1.5%.