Define prevalence.

• A. Fraction of a population having a specific disease at a given time
• B. Number of new cases per unit time
• C. Number of people who have ever had the disease
• D. Number of deaths due to disease per population

Answer: (A)

Prevalence is the proportion of people in a population who have a disease at a specific moment (point prevalence) or during a defined period (period prevalence). It represents the current burden of the disease in the population and is calculated as the number of existing cases divided by the total population. This measure reflects both how many people have the disease and how long they live with it, since longer duration increases the number of existing cases. It’s different from incidence, which counts new cases arising over time. The described option matches prevalence, while lifetime prevalence refers to anyone who has ever had the disease, and mortality rate refers to deaths due to the disease per population.