Effect of Indoor Residual Spraying on the Incidence of Malaria in Kaoma District of Western Zambia

Abstract

Background: Indoor residual spraying (IRS), the application of a chemical to the internal walls of the structure in order to kill an insect that sits on the wall treated with such a chemical, is one of the methods adopted by World Health Organisation in combating malaria by controlling the vector mosquito. In line with the Zambian policy on malaria control Kaoma district in Western province of Zambia in 2008, started implementing IRS as the method of combating malaria. The main purpose of the study was to ascertain the effect of indoor residual spraying on incidence of malaria in Kaoma district of Western Province of Zambia.
Materials and Methods: The study was a retrospective cohort analysis of incidence data across a single spray season, mixed with cross sectional survey to assess levels of intervention, community understanding and perceptions, and quality of IRS efforts, which were compared with households sprayed. Interviewees included household heads or the representative. The other party interviewed included the supervisors for the IRS program. Multistage sampling was used to select respondents from households and probability proportional to size (PPS) was used to select clusters in which respondents were picked. To validate the findings of the study, statistical significance was set at p < 0.05.
Results: The study demonstrated that areas with a larger percentage of the population (greater than 60%) protected by Indoor residual spraying had lower incidence of malaria (82/1000 and 400/1000) compared to unsprayed area (398/1000 and 773/1000) both at the beginning and pick of malaria transmission season. A chi-square test shows that there was an association between spraying and reduced malaria incidence, p <0.05. Factors such as length of Insecticide Treated Nets ownership and building material for the house (p-value<0.04 and 0.03) respectively, had an association with the level of IRS acceptance. Acceptance of indoor residual spraying program was good at 64% of the 100% response rate interviewed. Reasons given for those who did not have the houses sprayed among others was absence from home (79%). There was an association between Knowledge of the use for IRS and school attendance p-value < 0.001. Management of the program was poor, negatively affecting results of indoor residual spraying, starting from ill timing (wrong season) to management of commodities such as personal protective equipment, Insecticide, inadequate transport and short notice given to the households. 
Conclusion: Indoor residual spraying was associated with reduced malaria incidence in Kaoma district in areas where it was implemented. Poor management of the programme, however, negatively affected the results. The district needs to focus on management of logistics, intensify sensitisation and improve on the starting time of IRS if it has to have the desired impact in preventing malaria.