Which statement correctly defines incidence and prevalence?

• A. Incidence is the total number of existing cases at a given time; Prevalence is the rate of new cases over a period in a population at risk.
• B. Incidence is the rate of new cases over a period in a population at risk; Prevalence is the total number of existing cases at a given time.
• C. Both incidence and prevalence measure new cases over time.
• D. Prevalence measures only severe cases while incidence measures all new cases.

Answer: (B)

Incidence vs prevalence describes two different ways of looking at disease in a population. Incidence is the rate at which new cases occur over a specified period in the population that is at risk, usually expressed as a rate (for example, new cases per 1,000 people per year). Prevalence is the total number of existing cases at a given time, reflecting how widespread the disease is at that moment, typically expressed as a proportion or percent. So the statement that incidence is the rate of new cases over a period in a population at risk, while prevalence is the total number of existing cases at a given time, is correct. This highlights the distinct roles: incidence measures risk of developing disease, prevalence measures overall disease burden. The other options mix up these definitions or add unsupported claims (for example, prevalence counting only severe cases).