Evaluation of a sampling methodology for the Rapid Assessment of Aedes aegypti infestation levels in Iquitos, Perú

ABSTRACT

An epidemic of dengue during 2001 in Northwestern Peru has re-emphasized the need for efficient, accurate, and economical vector surveillance methods. Between November 1998 and January 1999 we carried out extensive entomological surveys in two neighborhoods (Maynas and Tupac) of 600 contiguous houses (14-20 blocks) each located in the Amazonian city of Iquitos, which has provided a unique opportunity to evaluate the Aedes aegypti rapid assessment survey strategy. This strategy is based on PAHO recommendations employed by the Peruvian Ministry of Health (MOH). All household locations from 4 surveys (2/neighborhood), including closed and unoccupied houses were georeferenced and displayed in a Geographic Information System (GIS), facilitating simulations of 10 MOH surveys based on hypothetical systematic sampling transects for 3 work groups (15-25 houses per group starting from randomly selected blocks). Larval, pupal and adult mosquito indices were calculated for each simulation and compared to the indices calculated from the complete data set. Infestation rates were highest in Maynas where House Indices (HI proportion of houses positive for larvae) were 45% and 38% in surveys 1 and 2, respectively. In Tupac Amaru the HI was 30% in survey 1 and 27% survey 2. The observed range in simulated House indices in Maynas survey 1 and 2 were 38-56% and 36-42%; whereas in Tupac they were 21-34% and 13-33%. Index stability was evaluated by comparing the coefficient of variation to the mean of the simulation results. HI, Breteau index, pupae/ha, adult index, and adults/ha were more robust entomological indicators (CV/mean=0.1-2.9), than the container index, pupae/person, pupae/house, adults/person, and adults/house (CV/mean>20). Results demonstrate that the MOH's Aedes aegypti risk assessment program provides reasonable estimates of actual indices; however, the further understanding of the association of these indices with rates of virus transmission...