Seasonal climate patterns and their impact on mosquito net use in Nigeria: evidence from repeated surveys.

Consistent use of insecticide-treated nets (ITNs) for malaria prevention has been a challenge undermining the intervention's effectiveness. Perceptions of heat and absence of mosquitoes are among the reasons cited for non-use of ITN in populations with access. We conducted repeated household surveys across seasons in Ondo State of Nigeria to investigate seasonal changes in ITN use rates and potential determinant factors. Five household surveys were conducted in different months before an ITN distribution campaign in December 2021 followed by post-campaign surveys in April 2022, and in June, August and October 2023. Temperature and precipitation estimates up to 60 days before each of the surveys were used to investigate the potential effects of seasonal factors on proportions of people using ITNs among those with access (use behaviour). The study found significant associations between climatic factors and ITN use, with increases in the rainy season and reductions in the hot, dry season. Temperature and precipitation were negatively and positively associated with ITN use among populations with access respectively, suggesting the effects of heat and potentially mosquito abundance and perceived risk of malaria. A mixed-effects regression showed that each 1 °C increase in mean temperature during the 30 days preceding surveys was associated with a 9 percentage point decrease in ITN use rate (p = 0.006). Rainfall showed a smaller but significant positive association with ITN use. Each additional 10 mm of rainfall 31-60 days before surveys increased use rate by 0.7 percentage points (p = 0.013). Higher proportions of low-SES households within study clusters and a greater number of nets per person were significantly associated with increased ITN use, independent of climatic influences. Although overall ITN use is largely determined by access, this study provides evidence that, among populations with access, usage is further influenced by a complex interplay of multiple factors and climatic fluctuations. While previous research has explored associations between climate and ITN use, this study strengthens the evidence through state-level, repeated, within-population serial cross-sectional observations. The findings indicate that seasonal variations in rainfall and temperature are key determinants of ITN use behaviour. These patterns should inform the design of behaviour change communication strategies, as well as the timing of distribution campaigns and evaluation surveys. Interpretations of ITN use survey data should account for seasonal effects.