Impact of a spatial repellent on malaria incidence in two villages in Sumba, Indonesia

Abstract

A randomized, double-blinded, placebo-controlled study was conducted to examine the effect of spatial repellent (SR) in households at risk of malaria in Indonesia. Following presumptive radical cure for malaria in 180 adult men representing sentinels of new infection in four clusters within two villages, all households were given either metofluthrin or placebo mosquito coils. Weekly blood smear screening and human-landing mosquito catches were done throughout the 6 months intervention. Malaria infections occurred in 61 subjects living in placebo households and 31 subjects living in SR coil households, suggesting a 52% protective effect of SR. Likewise, anopheles indoor human landing rates were 32% lower in homes receiving SR coils. Differences in the malaria attack rate between SR- and placebo-treated homes was significant when not accounting for the effects of clustering. When the analysis was adjusted for intra-cluster correlation, the differences between SR- and placebo-treated homes were not statistically significant. The findings provide evidence of SR public health benefit and support a larger trial statistically powered to detect those effects.

Figure 1.

Map of the study site (box) in the Southwest Sumba District and its location in the Indonesian archipelago (map not to scale). The District is located in the western part of Sumba Island (insert).

Figure 2.

Map of the household clusters in the Umbungedo and Wainyapu villages. Four clusters: U1, U2, W1, and W2 (grayed) were selected, each consisted of ca. 100 households and 500 people each.

Figure 3.

Flowchart of the screening and enrollment of study volunteers. Two hundred and thirty-one subjects were screened for G6PD deficiency and 180 consented to be enrolled and provided radical cure for malaria of which 170 completed the treatment and subsequently followed up for 6 months during the intervention.

Figure 4.

Cumulative weekly indoor attack rates of Anopheles sundaicus, pooled by village cluster in Wainyapu and Umbungedo, respectively. Both villages showed significantly different indoor Anopheles biting densities between active and placebo houses during 26 weeks of observation.