The impact of indoor residual spraying on malaria incidence in East Shoa Zone, Ethiopia

BACKGROUND In Ethiopia, nearly 70% of the population resides in areas prone to malaria infection. The objective of this study is to evaluate the impact of indoor residual spraying (IRS) on the incidence of malaria in East Shoa Zone of Ethiopia. METHODS Data from the registers of malaria cases at Debrezeit Malaria Control Center in East Shoa Zone of Ethiopia were collected and analyzed. Records of 22 villages with no previous rounds of spraying that were entirely covered with IRS using DDT during the peak malaria transmission season of 2001 and 2002 and other 22 adjacent villages with similar malaria incidence but remained unsprayed were used for the analyses. RESULTS The incidence of malaria in 2011 and 2002 among the sprayed villages was lower than the respective preceding years for both Plasmodium species (incidence rate ratio 0.60; CI 0.35 to 0.95; p < 0.0001). After the focal spray, there was significant reduction in malaria incidence in the villages sprayed. Spraying was associated with a 62% reduction in malaria incidence. CONCLUSIONS This study demonstrated that IRS with DDT was effective in reducing malaria incidence in highland epidemic-prone areas in the East Shoa Zone of Ethiopia. A larger scale study should evaluate the effectiveness of DDT in reducing malaria incidence against its environmental impact and alternative strategies for malaria prevention.