Longlasting insecticidal nets for prevention of Leishmania donovani infection in India and Nepal: paired cluster randomised trial

Abstract

Objective: To test the effectiveness of large scale distribution of longlasting nets treated with insecticide in reducing the incidence of visceral leishmaniasis in India and Nepal. Design: Paired cluster randomised controlled trial designed to detect a 50% reduction in incidence of Leishmania donovani infection. Setting: Villages in Muzaffarpur district in India and Saptari, Sunsari, and Morang districts in Nepal. Participants: 13 intervention and 13 control clusters. 12 691 people were included in the analysis of the main outcome (infection), and 19 810 were enrolled for the secondary (disease) end point. Intervention: Longlasting insecticidal nets (treated with deltamethrin) were distributed in the intervention clusters in December 2006. Main outcome measures: Infection was determined by direct agglutination test at 12 and 24 months after the intervention in those who had negative results (titre <1:1600) at baseline. The effect estimate was computed as the geometric mean of the risk ratios for seroconversion for each cluster pair (net/no net), with its 95% confidence interval. Formal tests of effect of no intervention were obtained with a paired t test. Results: There was no significant difference in the risk of seroconversion over 24 months in intervention (5.4%; 347/6372) compared with control (5.5%; 345/6319 people) clusters (risk ratio 0.90, 95% confidence interval 0.49 to 1.65) nor in the risk of clinical visceral leishmaniasis (0.99, 0.46 to 1.40). Adjustment for covariates did not alter these conclusions. Conclusions: There is no evidence that large scale distribution of longlasting insecticidal nets provides additional protection against visceral leishmaniasis compared with existing control practice in the Indian subcontinent. The observed effect was small and not significant, though the confidence intervals did not exclude a 50% change in either direction.