The IRS refers to the application of insecticide to the interior walls of homes.
The study, carried out by the Wits Research Institute for Malaria (WRIM) and the London School of Hygiene and Tropical Medicine (LSHTM), was published in The Lancet February 25, 2021.
Targeted indoor or blanket residual spraying
Malaria still represents one of the biggest health crises in the world, especially on the African continent where 94% of cases and deaths occur (World Health Organization, 2020).
Most countries in southern Africa have set the elimination of malaria within their borders as a political goal.
In South Africa IRS has been used effectively since 1945. As a result, malaria transmission is low, but persistent. Malaria transmission is confined to the border districts in the northeast of the provinces of Mpumalanga, Limpopo and KwaZulu-Natal.
IRS has been a very effective malaria control strategy in many countries. However, IRS is a logistical challenge when deployed on a large scale, and its costs are increasing, in part due to challenges in tackling the resistance of malaria-vector mosquitoes to cheap insecticides.
In addition, it can be unwarranted and unsustainable to spray all homes in areas where malaria is rare (but not eliminated), especially when resources are limited.
Globally, spending on malaria prevention and treatment has stagnated for nearly a decade, despite rising unit costs and population growth. More effective strategies are therefore urgently needed to support malaria elimination efforts in low transmission settings.
The increase in rural populations makes it very difficult to perform IRS at the recommended coverage of 85% of all households before the malaria transmission season is in full swing. Reactive spraying and substantial savings make [targeted IRS] an effective strategy to be adopted by national and provincial malaria control programs – based on good science. “
Maureen Coetzee, study co-author and professor emeritus, Wits Malaria Research Institute
About the study
The study, titled Efficacy and Cost-Effectiveness of Reactive and Targeted Indoor Residual Spray for Malaria Control in Low Transmission Settings: A Randomized Cluster Non-inferiority Trial in South Africa, was the first to determine if reactive and targeted IRS is not lower and more cost effective compared to the standard practice of an annual mass spray campaign before the malaria season.
The trial was carried out in residential areas (clusters) in Bushbuckridge, Mpumalanga and Phalaborwa, Limpopo province.
The clusters were randomly assigned to the targeted approach or the standardized approach. In the intervention arm of the trial, teams sprayed houses only in response to a reported malaria case and limited spraying to that one house. [the index case house] and up to eight neighboring houses within 200m.
The targeted intervention therefore involved a substantial reduction in spraying, intended only for areas where there had been recent evidence of malaria transmission as indicated by the occurrence of a recent case of malaria.
Safe and profitable strategies
The results proved that, within the predefined range of 1 case per 1000 people per year, the targeted approach was no worse than the standard approach. In addition, the targeted approach has proven to be very cost effective.
The average annual economic cost was $ 88,258 (± 2 million rand, 2017 exchange rate) per 100,000 population for the targeted intervention, which is 52% less expensive than the standard practice, which costs $ 184,319 (± 2.5 million of R2, 2017 exchange rate).
“The targeted intervention is less expensive because it involved spraying significantly fewer structures, did not use contract sprayers, and used significantly less insecticide, transport and equipment,” says David Bath, researcher in health economics at LSHTM and co-author of the study with Dr Jackie Cook, associate professor in malaria epidemiology at LSHTM.
Targeted transmission solutions
The authors recognize that replacing an existing intervention, which has been common practice for many years, would be politically and socially sensitive and would require vigilance to avoid a resurgence of cases. It is therefore important that strategies that reduce costs through better IRS targeting are based on solid evidence, as this study demonstrates.
Mr. Aaron Mabuza, co-chair of the South African Committee for the Elimination of Malaria (SAMEC), co-author of the study and former director of the provincial malaria program in Mpumalanga, said: “I was wondering if there was an alternative to PID coverage and this IRS targeted study answered my question. The recommendations are realistic and applicable, and also address the problem of population growth, which now makes it nearly impossible to complete general IRS before the onset of heavy transmission. “
The targeted IRS ensures the reallocation of saved resources to other vital malaria control and elimination activities, such as improved awareness campaigns, case management, surveillance and epidemic preparedness.
“The study results represent an exciting development to divest funds into other areas contributing to malaria elimination in very low transmission settings across southern Africa,” says Coetzee.
Bath, D., et al. (2021) Efficacy and cost-effectiveness of reactive and targeted indoor residual spray for malaria control in low transmission settings: a cluster randomized non-inferiority trial in South Africa. Lancet. doi.org/10.1016/S0140-6736(21)00251-8.