A population of 100000 is under surveillance during a year. 100 cases were positive for malarial thick smear. 20 developed complications and 10 died among cases. What is the Annual parasite incidence?

**Core Concept**
The Annual Parasite Incidence (API) is a measure of the number of new malaria cases occurring in a population per 1000 population per year. It is an indicator of the malaria transmission intensity in a given area.

**Why the Correct Answer is Right**
API is calculated as the number of new malaria cases occurring in a year divided by the mid-year population of the area, multiplied by 1000. The formula for API is: (Number of new cases in a year / Mid-year population) * 1000. In this scenario, the number of new cases is 100, and the mid-year population is 100,000. Therefore, the API would be (100 / 100,000) * 1000 = 1.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, so we'll move on to the others.
**Option B:** Assuming it's a different value, it would be incorrect if it doesn't match the correct calculation.
**Option C:** This option would be incorrect if it's a different value or if it's not the correct formula for API.
**Option D:** This option would be incorrect if it's a different value or if it's not the correct formula for API.

**Clinical Pearl / High-Yield Fact**
Remember that API is a useful tool for monitoring malaria transmission intensity and evaluating the effectiveness of control measures in a given area.

**Correct Answer:** A. 1.

✓ Correct Answer: A. 1 per 1000