A malarial survey is conducted in 50 villages having a population of one lakh. Out of 20000 slides examined, 500 turned out to be malaria positive. The annual parasite incidence is -

<> -Annual parasite incidence. = confirmed cases during one year *1000 ---------------------------------------------------------- Population under surveillance (0.5%) -It is based on intensive active and passive surveillance and cases are confirmed by blood examination. Reference : Park's textbook of preventive and social medicine, 23rd edition, pg no:261 <\>