A cluster-randomized controlled trial to assess the effectiveness of using 15% DEET topical repellent with long-lasting insecticidal nets (LLINs) compared to a placebo lotion on malaria transmission

Abstract

Background: Long-lasting insecticidal nets (LLINs) have limited effect on malaria transmitted outside of sleepin hours. Topical repellents have demonstrated reduction in the incidence of malaria transmitted in the early evening This study assessed whether 15% DEET topical repellent used in combination with LLINs can prevent greate malaria transmission than placebo and LLINs, in rural Tanzania Methods: A cluster-randomized, placebo-controlled trial was conducted between July 2009 and August 201 in a rural Tanzanian village. Sample size calculation determined that 10 clusters of 47 households with fiv people/household were needed to observe a 24% treatment effect at the two-Tailed 5% significance level, wit 90% power, assuming a baseline malaria incidence of one case/person/year. Ten clusters each were randoml assigned to repellent and control groups by lottery. A total of 4,426 individuals older than six months were enrolled. Al households in the village were provided with an LLIN per sleeping space. Repellent and placebo lotion wa replaced monthly. The main outcome was rapid diagnostic test (RDT)-confirmed malaria measured by passiv case detection (PCD). Incidence rate ratios were estimated from a Poisson model, with adjustment for potentia confounders, determined a priori. According-To-protocol approach was used for all primary analyses Results: The placebo group comprised 1972.3 person-years with 68.29 (95% C.I 37.05-99.53) malaria cases/1,00 person-years. The repellent group comprised 1,952.8 person-years with 60.45 (95% C.I 48.30-72.60) cases/1,00 person-years, demonstrating a non-significant 11.44% reduction in malaria incidence rate in this group, (Wilcoxo rank sum z = 0.529, p = 0.596). Principal components analysis (PCA) of the socio-economic status (SES) of the tw groups demonstrated that the control group had a higher SES (Pearson's chi square = 13.38, p = 0.004) Conclusions: Lack of an intervention effect was likely a result of lack of statistical power, poor capture of malari events or bias caused by imbalance in the SES of the two groups. Low malaria transmission during the stud period could have masked the intervention effect and a larger study size was needed to increase discriminator power. Alternatively, topical repellents may have no impact on malaria transmission in this scenario. Design an implementation of repellent intervention studies is discussed Trial registration: The trial was registered ISRCTN92202008-http://www.controlled-Trials.com/ISRCTN9220200.