Efficacy of ceiling-mounted mosquito nets for malaria vector control in a Peruvian Amazon riverine community: A stepped-wedge cluster randomized trial.

Malaria remains a major global health concern, especially in tropical regions such as the Peruvian Amazon. Installing ceiling-mounted mosquito nets in houses has been proposed as a strategy to reduce mosquito-human contact and, in turn, lower malaria transmission. We aimed to assess the effectiveness of ceiling-mounted mosquito nets in reducing Anopheles mosquito density in a high-transmission Amazonian setting. We conducted a stepped-wedge cluster-randomized trial from March to December 2024 in the Llanchama community of the San Juan Bautista district, Loreto, Peru. A total of 69 households were randomized into three clusters, receiving the intervention at staggered three-month intervals. We measured entomological indices using human landing catches (HLC) and other standardized methods, focusing on Anopheles mosquito counts, bites per person per night (BPN), and bites per person per hour (BPH), both indoors and peridomestic, derived from the same HLC sessions, using cumulative mosquito captures over 12-hour periods to compute biting indices. Houses were retrofitted with mosquito nets across ceilings and other open structural areas, creating a barrier to prevent mosquito entry and lower exposure. Analysis followed a stepped-wedge mixed-effects negative binomial model adjusting for clustering and time trends. Our per-protocol analysis shows that, compared to non-renovated households, the renovated households experienced a 55% reduction in indoor Anopheles counts (95% CI: 33%-74%; p = 0.004), a 60% decrease in indoor BPN (95% CI: 27%-78%; p = 0.003), and a 61% reduction in indoor BPH (95% CI: 15%-83%; p = 0.018). Peridomestic mosquito counts, BPN, and BPH did not differ significantly between renovated and non-renovated households. Our study provides evidence that installing mosquito nets across household ceilings markedly reduces indoor Anopheles presence and biting rates, suggesting that this structural modification could be a promising strategy for lowering malaria risk in riverine communities.