Abstract
BackgroundSégou Region in central Mali is an area of high malaria burden with seasonal transmission. The region reports high access to and use of long-lasting insecticidal nets (LLINs), though the principal vector, Anopheles gambiae, is resistant to pyrethroids. From 2011 until 2016, several high-burden districts of Ségou also received indoor residual spraying (IRS), though in 2014 concerns about pyrethroid resistance prompted a shift in IRS products to a micro-encapsulated formulation of the organophosphate insecticide pirimiphos-methyl. Also in 2014, the region expanded a pilot programme to provide seasonal malaria chemoprevention (SMC) to children aged 3–59 months in two districts. The timing of these decisions presented an opportunity to estimate the impact of both interventions, deployed individually and in combination, using quality-assured passive surveillance data.MethodsA non-randomized, quasi-experimental time series approach was used to analyse monthly trends in malaria case incidence at the district level. Districts were stratified by intervention status: an SMC district, an IRS district, an IRS + SMC district, and control districts that received neither IRS nor SMC in 2014. The numbers of positive rapid diagnostic test (RDT +) results reported at community health facilities were aggregated and epidemiological curves showing the incidence of RDT-confirmed malaria cases per 10,000 person-months were plotted for the total all-ages and for the under 5 year old (u5) population. The cumulative incidence of RDT + malaria cases observed from September 2014 to February 2015 was calculated in each intervention district and compared to the cumulative incidence reported from the same period in the control districts.ResultsCumulative peak-transmission all-ages incidence was lower in each of the intervention districts compared to the control districts: 16% lower in the SMC district; 28% lower in the IRS district; and 39% lower in the IRS + SMC district. The same trends were observed in the u5 population: incidence was 15% lower with SMC, 48% lower with IRS, and 53% lower with IRS + SMC. The SMC-only intervention had a more moderate effect on incidence reduction initially, which increased over time. The IRS-only intervention had a rapid, comparatively large impact initially that waned over time. The impact of the combined interventions was both rapid and longer lasting.ConclusionEvaluating the impact of IRS with an organophosphate and SMC on reducing incidence rates of passive RDT-confirmed malaria cases in Ségou Region in 2014 suggests that combining the interventions had a greater effect than either intervention used individually in this high-burden region of central Mali with pyrethroid-resistant vectors and high rates of household access to LLINs.
Highlights
Ségou Region in central Mali is an area of high malaria burden with seasonal transmission
Effective supplementary interventions are becoming more widely available and—in the face of stalled progress and growing concerns about insecticide resistance—more important [1, 3, 4]. This situation naturally leads to questions about how to best layer new tools on top of existing ones to maximize programme impact across various transmission settings [5]. Both with World Health Organization (WHO) policy recommendations, are (1) indoor residual spraying (IRS) [6], including the use of third-generation IRS products (3GIRS; products defined as insecticide formulations that are effective at controlling pyrethroid-resistant mosquitoes for at least 6 months) and (2) seasonal malaria chemoprevention (SMC) with sulfadoxine-pyrimethamine plus amodiaquine (SP + Sulfadoxine-pyrimethamine plus amodiaquine (AQ)) in children under 5 years of age [7]
The impact of IRS and IRS + SMC were both highly statistically significant, though overlapping inci- Results dence rate ratios (IRR) confidence intervals indicate that the overall cumulative trends towards greater reduction in the combined intervention district compared to the IRS only intervention district were not statistically significant
Summary
Ségou Region in central Mali is an area of high malaria burden with seasonal transmission. Effective supplementary interventions are becoming more widely available and—in the face of stalled progress and growing concerns about insecticide resistance—more important [1, 3, 4] This situation naturally leads to questions about how to best layer new tools on top of existing ones to maximize programme impact across various transmission settings [5]. Two additional strategies, both with WHO policy recommendations, are (1) indoor residual spraying (IRS) [6], including the use of third-generation IRS products (3GIRS; products defined as insecticide formulations that are effective at controlling pyrethroid-resistant mosquitoes for at least 6 months) and (2) seasonal malaria chemoprevention (SMC) with sulfadoxine-pyrimethamine plus amodiaquine (SP + AQ) in children under 5 years of age [7]. These monthly treatments maintain therapeutic drug concentrations in the blood during the peak transmission period, thereby preventing malaria illness in the target population [9]
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