Enhanced protection against malaria by indoor residual spraying in addition to insecticide treated nets: is it dependent on transmission intensity or net usage?

Philippa A West, Natacha Protopopoff, Alexandra Wright, Zuhura Kivaju, Robinson Tigererwa, Franklin W Mosha, William Kisinza, Mark Rowland, Immo Kleinschmidt, Philippa A West, Natacha Protopopoff, Alexandra Wright, Zuhura Kivaju, Robinson Tigererwa, Franklin W Mosha, William Kisinza, Mark Rowland, Immo Kleinschmidt

Abstract

Background: Insecticide treated nets (ITNs) and indoor residual spraying (IRS) are effective vector control tools that protect against malaria. There is conflicting evidence regarding whether using ITNs and IRS in combination provides additional benefit over using either of these methods alone. This study investigated factors that may modify the effect of the combined use of IRS and ITNs compared to using ITNs alone on malaria infection prevalence.

Methods: Secondary analysis was carried out on data from a cluster randomised trial in north-west Tanzania. 50 clusters received ITNs from a universal coverage campaign; of these 25 were randomly allocated to additionally receive two rounds of IRS in 2012. In cross-sectional household surveys children 0.5-14 years old were tested for Plasmodium falciparum infections (PfPR) two, six and ten months after the first IRS round.

Results: IRS protected those sleeping under nets (OR = 0.38, 95%CI 0.26-0.57) and those who did not (OR = 0.43, 95%CI 0.29-0.63). The protective effect of IRS was not modified by community level ITN use (ITN use<50%, OR = 0.39, 95%CI 0.26-0.59; ITN use> = 50%, OR = 0.46, 95%CI 0.28-0.74). The additional protection from IRS was similar in low (<10% PfPR, OR = 0.38, 95%CI 0.19-0.75) and high transmission areas (≥10% PfPR, OR = 0.34, 95%CI 0.18-0.67). ITN use was protective at the individual-level regardless of whether the village had been sprayed (OR = 0.83, 95%CI 0.70-0.98). Living in a sprayed village was protective regardless of whether the individual slept under an ITN last night (OR = 0.41, 95%CI 0.29-0.58).

Interpretation: Implementing IRS in addition to ITNs was beneficial for individuals from villages with a wide range of transmission intensities and net utilisation levels. Net users received additional protection from IRS. ITNs were providing some individual protection, even in this area with high levels of pyrethroid insecticide resistance. These results demonstrate that there is a supplementary benefit of IRS even when ITNs are effective.

Trial registration: ClinicalTrials.gov NCT01697852.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1. Study timetable.
Fig 1. Study timetable.
Note: Surveys 1 and 2 are baseline surveys. Surveys A, B and C are post intervention.
Fig 2. Trial profile for study households…
Fig 2. Trial profile for study households and children in the ITN only and ITN+IRS study arms.
Note: Survey A = 2 months after first intervention spray. Survey B = 6 months after first intervention spray and 2 months after second intervention spray. Survey C = 10 months after first intervention spray and 6 months after second intervention spray. *No children 0.5–14 y old. 1Dwelling vacant for survey duration. 2Includes not found (91.0%), not visited (2.4%), and missing data (6.6%). 3Households (HH) that were included and where children attended for testing.

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Source: PubMed

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