In a survey of 100 dogs, 10 had heartworm. What is the prevalence?

• A. 5%
• B. 10%
• C. 1%
• D. 15%

Answer: (B)

Prevalence is the proportion of individuals in a defined population who have the disease at a specific point in time. In this survey, 10 dogs are heartworm-positive out of 100 dogs examined. So prevalence = 10/100 = 0.10, which equals 10%. The other percentages would correspond to different counts (5 of 100 would be 5%, 1 of 100 would be 1%, 15 of 100 would be 15%), which do not match the observed data. If the question were about new cases over a period, that would reflect incidence, not prevalence.