Indoor Residual Spraying for Malaria Control in Sub-Saharan Africa 1997 to 2017: An Adjusted Retrospective Analysis

Abstract

Background: Indoor residual spraying (IRS) is a key tool for controlling and eliminating malaria by targeting vectors. To support the development of effective intervention strategies it is important to understand the impact of vector control tools on malaria incidence and on the spread of insecticide resistance. In 2006, the World Health Organization (WHO) stated that countries should report on coverage and impact of IRS, yet IRS coverage data are still sparse and unspecific. Methods: Data on IRS deployment were collated from a variety of sources, including the President's Malaria Initiative spray reports and National Malaria Control program reports, for all 46 malaria-endemic countries in Sub-Saharan Africa from 1997 to 2017. The data were mapped to the applicable administrative divisions and the proportion of households sprayed for each of the four main insecticide classes; carbamates, organochlorines, organophosphates and pyrethroids was calculated. Findings: The number of countries implementing IRS has increased considerably although coverage in-country is often low, particularly in West Africa. From 1997 to 2010 there was an expansion of IRS using organochlorines (DDT) and pyrethroids. From 2011, carbamates partly replaced these insecticides and organophosphate use increased from 2013 onwards, however, policy recommendations to rotate between insecticide classes were rarely followed. Interpretation: Our results highlight trends in IRS coverage and insecticide choice in sub Saharan Africa. The data presented here can improve studies on the impact of IRS on malaria incidence and on insecticide resistance development and help to guide future malaria control efforts. Funding Statement: Wellcome Trust grant 108440/Z/15/Z. Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: Not Required.