All 72 patients in a chronic hemodialysis center were tested for hepatitis C. Eight of the patients were identified as HCV positive. What is the prevalence of HCV among the patients at the center?

• A. 8%
• B. 11%
• C. 72%
• D. 22%

Answer: (B)

Prevalence describes the proportion of people in a defined population who have a condition at a specific point in time. Here, eight patients are hepatitis C positive out of a total of seventy-two tested. So, 8 divided by 72 equals about 0.111, which is 11%. This is a snapshot of how widespread the infection is in that group at that moment, not the rate of new cases over time (incidence). The other percentages don’t fit: 8% would correspond to roughly 6 people, 72% would be far more than eight, and 22% would be about 16, so the exact interpretation is about 11%.