Targeted anti-malarial spraying as safe and more cost effective

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Targeted Indoor Residual Spraying (IRS) intervention against malaria is not inferior to the “blanket” approach, as well as being more cost effective, found a study by University of the Witwatersrand and the London School of Hygiene and Tropical Medicine, published in The Lancet.

Savings could potentially be reallocated to other malaria control and elimination activities,

The study was undertaken by the Wits Research Institute for Malaria (WRIM) and the London School of Hygiene and Tropical Medicine (LSHTM).

Malaria still represents one of the world’s largest health crises, particularly on the African continent where 94% of cases and deaths occur (World Health Organisation, 2020). Most countries in southern Africa have set the elimination of malaria within their borders as a policy target.

In South Africa, IRS  – the application of insecticide onto the interior walls of houses – has been effectively used since 1945. As a result, malaria transmission is low, but persistent. Malaria transmission is confined to the north-eastern border districts of Mpumalanga, Limpopo, and KwaZulu-Natal provinces.

IRS has been a highly effective strategy for controlling malaria in many countries. However, IRS is logistically challenging when deployed at scale and its costs are rising, due in part to the challenges posed in addressing resistance of malaria vector mosquitoes to low-cost insecticides. Furthermore, it may be unwarranted and unsustainable to spray all houses in areas where malaria is rare (but not eliminated), particularly when resources are limited.

At a global level, spending on malaria prevention and treatment has remained stagnant for almost a decade, despite rising unit costs and growing populations. More efficient strategies are therefore urgently required to sustain malaria elimination efforts in low transmission settings.

“The increase in rural populations makes it very difficult to carry out IRS at the recommended coverage of 85% of all households before the malaria transmission season is in full swing,” says Maureen Coetzee, distinguished professor in the WRIM and a co-author of the study. “Reactive spraying and the substantial cost-saving make (targeted IRS) an effective strategy for the national and provincial malaria control programmes to adopt – based on good scientific data.”

The study was the first to investigate whether reactive, targeted IRS is non-inferior and more cost-effective compared with the standard practice of an annual mass spray campaign ahead of malaria season. The trial was conducted in residential areas (clusters) in Bushbuckridge, Mpumalanga and in Phalaborwa, Limpopo province.

Clusters were randomly assigned to either the targeted or the standard approach. In the intervention arm of the trial, the teams only sprayed houses in response to a reported malaria case, and restricted spraying to just that house [the index case house] and up to eight neighbouring houses within 200m.

The targeted intervention therefore involved a substantial reduction in spraying, directed only at neighbourhoods where there had been recent evidence of malaria transmission as indicated by the occurrence of a recent malaria case.

The findings proved that, within the pre-specified margin of 1 case per 1000 people per year, the targeted approach was no worse than the standard approach. Furthermore, the targeted approach proved highly cost-effective.

The average annual economic cost was $88 258 (±R1.2m, 2017 exchange rate) per 100,000 population for the targeted intervention, which is 52% less costly than the standard practice, which costs $184 319 (±R2.5m, 2017 exchange rate).

“The targeted intervention cost less because it involved spraying far fewer structures, did not use contract sprayers, and used substantially less insecticide, transport, and equipment,” says David Bath, research fellow in health economics at LSHTM and joint first author of the study with Dr Jackie Cook, associate professor in malaria epidemiology at LSHTM.

The authors acknowledge that replacing an existing intervention, which has been standard practice for many years, would be politically and socially sensitive, and would require vigilance to avoid resurgence in cases. It is therefore important that strategies which reduce costs due to better targeting of IRS are based on robust evidence, as demonstrated by this study.

Aaron Mabuza, co-chair of the South African Malaria Elimination Committee (SAMEC), co-author of the study and former manager of the Mpumalanga Provincial Malaria Control Programme, says: “I used to wonder whether there was an alternative to blanket IRS and this study on targeted IRS has addressed my question. The recommendations are realistic and implementable, and also tackle the problem of population increase, which now makes it nearly impossible for blanket IRS to be completed before high transmission starts.”

Targeted IRS ensures the reallocation of saved resources to other life-saving malaria control and elimination activities, such as enhanced awareness campaigns, case management, surveillance, and epidemic preparedness

“The findings of the study represent an exciting development to divest funds into other areas contributing to malaria elimination in very low-transmission settings across southern Africa,” says Coetzee.

 

Study details
Effectiveness and cost-effectiveness of reactive, targeted indoor residual spraying for malaria control in low-transmission settings: a cluster-randomised, non-inferiority trial in South Africa

David Bath, Jackie Cook, John Govere, Phillemon Mathebula, Natashia Morris, Khumbulani Hlongwana, Jaishree Raman, Ishen Seocharan, Alpheus Zitha, Matimba Zitha, Aaron Mabuza, Frans Mbokazi, Elliot Machaba, Erik Mabunda, Eunice Jamesboy, Joseph Biggs, Chris Drakeley, Devanand Moonasar, Rajendra Maharaj, Maureen Coetzee, Catherine Pitt, Immo Kleinschmidt

Published in The Lancet on 27 February 2021

Abstract
Background
Increasing insecticide costs and constrained malaria budgets could make universal vector control strategies, such as indoor residual spraying (IRS), unsustainable in low-transmission settings. We investigated the effectiveness and cost-effectiveness of a reactive, targeted IRS strategy.
Methods
This cluster-randomised, open-label, non-inferiority trial compared reactive, targeted IRS with standard IRS practice in northeastern South Africa over two malaria seasons (2015–17). In standard IRS clusters, programme managers conducted annual mass spray campaigns prioritising areas using historical data, expert opinion, and other factors. In targeted IRS clusters, only houses of index cases (identified through passive surveillance) and their immediate neighbours were sprayed. The non-inferiority margin was 1 case per 1000 person-years. Health service costs of real-world implementation were modelled from primary and secondary data. Incremental costs per disability-adjusted life-year (DALY) were estimated and deterministic and probabilistic sensitivity analyses conducted. This study is registered with ClinicalTrials.gov, NCT02556242.
Findings
Malaria incidence was 0·95 per 1000 person-years (95% CI 0·58 to 1·32) in the standard IRS group and 1·05 per 1000 person-years (0·72 to 1·38) in the targeted IRS group, corresponding to a rate difference of 0·10 per 1000 person-years (–0·38 to 0·59), demonstrating non-inferiority for targeted IRS (p<0·0001). Per additional DALY incurred, targeted IRS saved US$7845 (2902 to 64 907), giving a 94–98% probability that switching to targeted IRS would be cost-effective relative to plausible cost-effectiveness thresholds for South Africa ($2637 to $3557 per DALY averted). Depending on the threshold used, targeted IRS would remain cost-effective at incidences of less than 2·0–2·7 per 1000 person-years. Findings were robust to plausible variation in other parameters.
Interpretation
Targeted IRS was non-inferior, safe, less costly, and cost-effective compared with standard IRS in this very-low-transmission setting. Saved resources could be reallocated to other malaria control and elimination activities.
Funding
Joint Global Health Trials.

 

University of the Witwatersrand material

 

The Lancet study (Open access)

 

Map of South African malaria transmission (2018)

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