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

Abstract

Summary 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.

Understudied Anophelines Contribute to Malaria Transmission in a Low-Transmission Setting in the Choma District, Southern Province, Zambia

“…Importantly, the association with households that had P. falciparum PCR-positive individuals indicates that targeting households with people who are parasitemic with vector control tools such as IRS and ITNs has the potential to affect the indoor vector populations. 35 It is unclear in our analysis whether there is a causal relationship with the number of mosquitoes and households with at least one person positive for P. falciparum . It is likely that households with greater mosquito counts may cause more cases, rather than households with positive individuals attracting more mosquitoes.…”

Prevention of re-establishment of malaria

“…Vector control services supported by entomological monitoring and investigation need to be maintained, to allow rapid intervention if there is an outbreak ( active focus ) or an imported case occurs in a receptive area [ 9 ]. While the strategic guidance is unchanged, it is regrettable that the term ‘ potential focus ’ used in earlier texts for the latter situation [ 2 ], is no longer promoted [ 3 ], although it is practical for planning (how many potential foci of what size are expected in an area per year?…”

Evaluating recurrent episodes of malaria incidence in Timika, Indonesia, through a Markovian multiple-state model

“…The reduction in malaria incidence in areas that use IRS on an ongoing basis can be 70–85% greater than in areas that do not use IRS ( Namuganga et al., 2021 ; Wagman et al., 2018 ). The use of IRS is also cheap, safe, and cost-effective, thereby freeing up other funds allocated for malaria treatment for use in control activities and other malaria elimination programs ( Bath et al., 2021 ; Wagman et al., 2018 ). In addition to providing wider and more effective protection, IRS and ITNs must also be accompanied by monitoring for their impacts on the environment and on malaria vectors themselves ( Hii, Hustedt, & Bangs, 2021 ).…”