<prompt> A population of 100000 is under surveillance during an year. 100 cases were positive for malarial thick smear. What is the annual parasite index ?1 per 10002 per 100010 per 100020 per 1000  <response>: Ans. is a i.e.,1 per 1000 Annual Parasite Incidence confirmed cases during one yearpopulation under surveillancee x 1000Population under surveillance 100000Confirmed cases 100 100API - x 1000 1 100,000So, API is 1 per 1000 population. 