Seasonal variation in the perceived risk of malaria: implications for the promotion of insecticide-impregnated bed nets.

Bed nets (mosquito nets), impregnated every 6 months with pyrethroid insecticides, are a simple, low-cost malaria control method well suited to conditions in sub-Saharan Africa. As large seasonal variations in levels of net usage may seriously limit the potential impact of the nets on malaria transmission, a study was conducted on local definitions of seasons, perceptions of seasonal variation in mosquito populations and incidence of febrile illnesses in Bagamoyo District, Tanzania, to aid in the design of a communication strategy for promoting sustained use of the nets. Both the diagnosis and treatment of febrile illnesses are affected by what season people think it is, by what illnesses they think are common in each season, and also by their perceptions of how abundant mosquitoes are. During dry seasons when mosquitoes are scarce and malaria is thought to be unlikely, it will be difficult to attain high rates of net usage. It will be necessary to develop locally-appropriate messages and communication materials that explain how it is possible that malaria can be a threat even when mosquitoes are few. Cultural consensus analysis was found to be a particularly valuable tool for understanding the reasons behind large variations in local perceptions of seasonality.