Towards a risk map of malaria for Sri Lanka: the importance of house location relative to vector breeding sites.

BACKGROUND In Sri Lanka, the major malaria vector Anopheles culicifacies breeds in pools formed in streams and river beds and it is likely that people living close to such breeding sites are at higher risk of malaria than people living further away. This study was done to quantify the importance of house location relative to vector breeding sites for the occurrence of malaria in order to assess the usefulness of this parameter in future malaria risk maps. Such risk maps could be important tools for planning efficient malaria control measures. METHODS In a group of seven villages in north central Sri Lanka, malaria cases were compared with community controls for distance from house to breeding sites and a number of other variables, including type of housing construction and use of anti-mosquito measures. The presence of An. culicifacies in bedrooms was determined by indoor insecticide spray collections. RESULTS People living within 750 m of the local stream, which was the established vector-breeding site, were at much higher risk for malaria than people living further away (odds ratio adjusted for confounding by other variables 5.93, 95% CI: 3.50-8.91). Houses close to the stream also had more adult An. culicifacies in the bedrooms. Poor housing construction was an independent risk factor for malaria. CONCLUSIONS Risk maps of malaria in Sri Lanka can be based on the location of houses relative to streams and rivers that are potential breeding sites for the malaria vector An. culicifacies. A distance of 750 m is suggested as the cut-off point in defining low- and high-risk villages.