DEET mosquito repellent sold through social marketing provides personal protection against malaria in an area of all-night mosquito biting and partial coverage of insecticide-treated nets: a case-control study of effectiveness.

DEET (diethyl-3-methylbenzamide), the widely used mosquito repellent, has the potential to prevent malarial infection but hitherto there has been no study demonstrating this possibility during normal everyday use. Mosbar, a repellent soap containing DEET, was promoted through social marketing in villages in eastern Afghanistan. This was followed up with a case-control study of effectiveness against malarial infection conducted through local clinics. Mosbar was purchased by 43% of households. Reported use of insecticide-treated nets (ITNs) was 65% among the control group. There was a strong association between Mosbar use and ITN use, as 81% of Mosbar users also possessed ITN. The use of Mosbar was associated with a 45% reduction in the odds of malaria (95% CI: -11% to 72%, P=0.08) after adjusting for ITN and other unmatched factors. Ownership of ITNs was associated with a 46% reduction in the odds of malaria (95% CI: 12% to 67%, P=0.013) after adjusting for Mosbar and other unmatched factors. The greatest reduction in the odds of malaria was associated with combined use of Mosbar and ITN (69% reduction, 95% CI: 28% to 87%, P=0.007). The association between recalled use of Mosbar 10 days ago (nearer the time of infection) and reduction in malarial infections (adjusted odds ratio 0.08, 95% CI: 0.01-0.61, P=0.001) was significantly stronger than that shown by current use of Mosbar. Most purchasers of Mosbar were satisfied with the product (74%), although a minority said they preferred to use only ITN (8%). The local mosquito vectors, Anopheles stephensi and A. nigerrimus, started biting shortly after dusk and continued biting until early morning. It was shown that Mosbar prevented biting throughout this period. In regions where mosquito vectors bite during evening and night, repellents could have a useful supplementary role to ITN and their use should be more widely encouraged.