Question

The incidence of a disease is 4 per 1000 of population with a duration of 2 years. Calculate the prevalence.

• A. 8/1000
• B. 4/1000
• C. 2/1000
• D. 6/1000

Hint:

Prevalence equals incidence multiplied by duration.

Answer 1

The Correct Option is A

Step 1: When a disease is in equilibrium, the number of existing cases (prevalence) builds up from the rate of new cases multiplied by how long each case lasts.

Step 2: This is captured by $P = I \times D$, so we simply combine the new-case rate with the mean duration.

Step 3: Plugging in an incidence of $4/1000$ and an average duration of $2$ years gives \[P = \frac{4}{1000} \times 2 = \frac{8}{1000}.\]
Step 4: So twice the annual incidence accumulates because each case persists for two years, giving a prevalence of 8 per 1000. \[\boxed{8/1000}\]