Data from a meta-regression analysis of 13 studies suggest indoor residual spraying reduced malaria prevalence by 62% in the developing world.
“A number of field studies have reported the effectiveness of indoor residual spraying in reducing malaria prevalence, but it is difficult to generalize from any single study how effective indoor residual spraying is at reducing malaria prevalence because various studies have shown conflicting results,” the researchers wrote. “Aspects of geography, entomology, human behavior and community acceptance of the program could contribute to why indoor residual spraying is more successful in one community than in another.”
Data were pooled from five electronic databases for articles in peer-reviewed journals that were published from 2000 to 2010; 13 studies were included in the analysis. Plasmodium falciparum accounted for most malaria infections in the studies. Four different insecticide types were used: pyrethroids (six studies), organochlorines (four studies), carbamates (two studies) and organophosphates (one study).
There was significant heterogeneity in the effect of indoor residual spraying across the studies, ranging from a RR of 0.01 to a RR of 0.9. The researchers found that the higher the prevalence of malaria, the lower the relative risk. In addition, they found that indoor residual spraying appears to be more effective when sprayed multiple times over a longer period of time.
The organochlorine class of insecticides, which includes DDT, was more effective at reducing malaria than the most commonly used pyrethroids. Finally, although P. falciparum malaria is associated with the greatest malaria mortality, the researchers found that indoor residual spraying was less effective against P. falciparum.
“To translate the promise of indoor residual spraying technology into wider application, we need a better understanding of the situational contexts behind different success levels of indoor residual spraying,” the researchers wrote. “To better inform future malaria control policy and actions, more monitoring and evaluation of indoor residual spraying campaigns is necessary to provide a full picture of how much indoor residual spraying can impact malaria burdens and what factors are determining indoor residual spraying effectiveness.”
Disclosure: The researchers report no relevant financial disclosures.