Cost and cost-effectiveness of indoor residual spraying with pirimiphos-methyl in a high malaria transmission district of Mozambique with high access to standard insecticide-treated nets

Sergi Alonso, Carlos J Chaccour, Joseph Wagman, Baltazar Candrinho, Rodaly Muthoni, Abuchahama Saifodine, Francisco Saute, Molly Robertson, Rose Zulliger, Sergi Alonso, Carlos J Chaccour, Joseph Wagman, Baltazar Candrinho, Rodaly Muthoni, Abuchahama Saifodine, Francisco Saute, Molly Robertson, Rose Zulliger

Abstract

Background: As malaria cases increase in some of the highest burden countries, more strategic deployment of new and proven interventions must be evaluated to meet global malaria reduction goals.

Methods: The cost and cost-effectiveness of indoor residual spraying (IRS) with pirimiphos-methyl (Actellic®300 CS) were assessed in a high transmission district (Mopeia) with high access to pyrethroid insecticide-treated nets (ITNs), compared to ITNs alone. The major mosquito vectors in the area were susceptible to primiphos-methyl, but resistant to pyrethoids. A decision analysis approach was followed to conduct deterministic and probabilistic sensitivity analyses in a theoretical cohort of 10,000 children under five years of age (U5) and 10,000 individuals of all ages, separately. Model parameters and distributions were based on prospectively collected cost and epidemiological data from a cluster-randomized control trial and a literature review. The primary analysis used health facility-malaria incidence, while community cohort incidence and cross-sectional prevalence rates were used in sensitivity analyses. Lifetime costs, malaria cases, deaths and disability-adjusted life-years (DALYs) were calculated to determine the incremental costs per DALY averted through IRS.

Results: The average IRS cost per person protected was US$8.26 and 51% of the cost was insecticide. IRS averted 46,609 (95% CI 46,570-46,646) uncomplicated and 242 (95% CI 241-243) severe lifetime cases in a theoretical children U5 cohort, yielding an incremental cost-effectiveness ratio (ICER) of US$400 (95% CI 399-402) per DALY averted. In the all-age cohort, the ICER was higher: US$1,860 (95% CI 1,852-1,868) per DALY averted. Deterministic and probabilistic results were consistent. When adding the community protective effect of IRS, the cost per person protected decreased (US$7.06) and IRS was highly cost-effective in children U5 (ICER = US$312) and cost-effective in individuals of all ages (ICER = US$1,431), compared to ITNs alone.

Conclusion: This study provides robust evidence that IRS with pirimiphos-methyl can be cost-effective in high transmission regions with high pyrethroid ITN coverage where the major vector is susceptible to pirimiphos-methyl but resistant to pyrethroids. The finding that insecticide cost is the main driver of IRS costs highlights the need to reduce the insecticide price without jeopardizing effectiveness.

Trial registration: ClinicalTrials.gov identifier NCT02910934 (Registered 22 September 2016). https://ichgcp.net/clinical-trials-registry/NCT02910934?term=NCT02910934&draw=2&rank=1.

Keywords: Economic evaluation; Indoor residual spraying; Insecticide-treated net; Mozambique; Vector control.

Conflict of interest statement

None declared.

Figures

Fig. 1
Fig. 1
Tornado diagrams showing results from univariate sensitivity analyses. Changes on the deterministic value of the incremental cost-effectiveness ratio (ICER) by changing the value of selected parameters when considering households’ direct and indirect costs (US$). Analyses consider: a children under five years of age (pre-adjustment ICER of US$403.92) and b individuals of all ages (pre-adjustment ICER of US$1,821.86). Changes on the selected parameters had no impact on ICERs in children under five years of age or individuals of all ages with the exception of changes on the efficacy of IRS with pirimiphos-methyl and the insecticide price, which made the intervention cost-effective in individuals of all ages. The vertical lines represent the maximum cost-effectiveness thresholds. DALY disability-adjusted life-year, IRS indoor residual spraying, OR odd ratio
Fig. 2
Fig. 2
Cost-effectiveness acceptability curves for the cohort of children under five years of age and individuals of all ages. The curves graphically represent the probability of adopting IRS with pirimiphos-methyl under high pyrethroid insecticide-treated nets (ITNs) being cost-effective at specific willingness-to-pay values, compared to not adopting IRS with pirimiphos-methyl under high pyrethroid ITN coverage. The vertical lines correspond to the standard cost-effectiveness thresholds by the World Health Organization. CE cost-effectiveness, Children U5 children under five years of age, DALY disability-adjusted life-year, IRS indoor-residual spraying

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