Effectiveness of a tailored forest package of interventions, including topical repellents, in reducing malaria incidence in Myanmar.

Background: In Myanmar, progress towards malaria elimination has stagnated in some areas requiring deployment of new tools and approaches to accelerate malaria elimination. While there is evidence that networks of community-based malaria workers and insecticide-treated nets (ITNs) can reduce malaria transmission in a variety of settings, evidence for the effectiveness of other interventions, such as topical repellents, is limited. Since malaria transmission in Myanmar occurs outdoors, mainly among forest-goers, this study tested the effectiveness of topical repellents in combination with supplemental ITN distribution and strengthened networks of malaria workers.

Methods: Thirty-eight villages in the Tanintharyi Region and Rakhine State were initially selected for the study based on malaria incidence in previous years. An additional 31 villages were included as comparison areas. The implementation of interventions began in March 2020 and continued through June 2021. Malaria cases were detected in all villages through surveillance at health facilities and a network of malaria workers. Data were analysed by interrupted time series. A nested case-control study was also conducted where forest-goers who tested positive for malaria by RDT were matched to up to three forest-goers who tested negative.

Results: A decrease in mean monthly incidence was observed in the intervention villages from 6.0 (95% CI 4.9-7.1) to 3.7 (95% CI 2.4-4.9) cases per 1000 people at risk before and after the interventions. For the comparison villages, the mean monthly incidence increased from 1.1 (95% CI 0.8-1.5) to 5.7 (95% CI 2.1-9.3) cases per 1000 people at risk. Malaria incidence was significantly lower following the implementation of the interventions (RR = 0.117; 95% CI 0.061-0.223; p < 0.001) in the intervention villages, whereas that of comparison villages was higher after the implementation of the interventions (RR = 3.558; 95% CI 0.311-40.750; p = 0.308). However, a significant trend for increasing malaria incidence after implementation was observed in the intervention villages (RR = 1.113; 95% CI 1.021-1.214, p = 0.015), suggesting a waning effect. The nested case-control analysis showed that the odds of topical repellent use were significantly lower among cases than controls (aOR: 0.063, 95% CI 0.013-0.313, p < 0.001).

Conclusion: The tailored intervention package for forest-goers helped reduce malaria incidence in Myanmar. Topical repellents may help to further reduce malaria transmission in elimination settings where high-risk populations such as forest-goers do not have easy access to routine health services or are less likely to use ITNs for malaria prevention.