Night-time location and sleeping behaviour of households in northern Benin: implications for residual malaria transmission and vector control

Abstract Background It is generally accepted that the declining effectiveness of core vector control tools — long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) — is partly explained by their misuse. Some household members remain outside, or move between indoor and outdoor spaces overnight, while sprayed walls and treated nets are designed to protect people who sleep indoors and under a net. Methods To determine whether communities that under-use these tools are more exposed to malaria vectors, direct participatory observation of household members' sleeping and activity patterns was carried out every 30 minutes from 19:00 to 07:00 in three departments of northern Benin. Binomial mixed-effects logistic regression (R 3.6, package lme4) was used to model the probability of household members being indoors versus outdoors as a function of season, time of night, collection area and IRS status, with household as a random effect. Results During the harmattan season, 95% of household members remained indoors from 19:00 to 07:00, compared with only 5% outdoors; this outdoor proportion declined steadily until 22:00. During the hot season, by contrast, 37% of households had members outdoors, with the majority remaining outside from 19:00 to 22:00. Household members were 4636 times more likely to stay indoors during the harmattan than during the hot season (adjusted odds ratio derived from β = 8.44). Populations in peripheral, non-IRS areas remained outdoors more than those in central, IRS-covered areas. Among household members exposed to bites outdoors, 65% cited irritation from indoor heat or insecticide as their main reason for staying outside, and 15% cited heat and lack of space. Overall, human exposure to Anopheles gambiae was higher outdoors than indoors, irrespective of the vector's host-feeding preferences. Conclusion Reducing residual malaria transmission will require raising community awareness of the correct use of LLINs and IRS, alongside complementary vector control tools designed for outdoor exposure.