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

In the fight against malaria, the strategy has long relied on two main defenses: sleeping under insecticide-treated nets and having the walls of homes sprayed with insecticide. These tools are designed to protect people while they sleep inside their houses, counting on the fact that the mosquitoes carrying the disease mostly bite at night when humans are resting indoors. However, the effectiveness of these tools can be compromised if people are not where the tools are. If a person stays outside in the evening or moves between the inside and outside of a home, they may escape the protection of the net or the sprayed walls, leaving them vulnerable to mosquito bites. Understanding exactly when and where people choose to be during the night is therefore critical for stopping the spread of the disease.

Researchers in northern Benin set out to map this behavior, focusing on how local families spend their nights during two distinct seasons: the hot, humid season and the harmattan, a period characterized by dry, dusty winds from the Sahara. They selected 96 households across three regions, ensuring a mix of villages that had recently received indoor spraying and those that had not. Instead of just asking people what they did, the team employed a method of direct observation. Trained observers, who were often members of the households themselves, recorded the location and activity of every family member every thirty minutes from 7:00 PM until 7:00 AM. They noted whether people were cooking, socializing, sleeping, or simply resting, and whether they were inside the house or out in the open.

The results revealed a striking difference in behavior depending on the time of year. During the cool, dry harmattan season, the pattern was predictable and protective: 95% of household members stayed inside their homes from evening until morning. The few who ventured outside did so only briefly, and by 10:00 PM, almost everyone was indoors. In contrast, the hot season told a different story. As temperatures rose, 37% of households had members spending time outside, with the majority remaining outdoors between 7:00 PM and 10:00 PM. It was not until late at night that people gradually moved inside. The researchers found that the heat and lack of space inside the homes were the primary drivers for this behavior. Many residents cited the discomfort of sleeping in hot rooms or irritation from the indoor insecticide spray as the main reasons for staying outside.

This shift in location has serious consequences because the mosquitoes that transmit malaria are also active during these evening hours. The study found that during the hot season, the risk of being bitten was actually higher outside than inside, regardless of whether the mosquitoes preferred to feed on humans inside or out. Even in areas where the walls had been sprayed, the protection was incomplete because so many people were outside when the mosquitoes were most aggressive. The data showed that people living on the edges of villages, away from the central areas where spraying was most concentrated, were more likely to remain outdoors than those in the center. Furthermore, the study highlighted that even when people were inside, many were not using their mosquito nets, leaving them exposed to bites even within the safety of their homes.

The findings suggest that the current tools, while valuable, are not enough on their own to stop transmission in this region. Because so many people are outside during the peak biting hours, especially in the hot season, the protection offered by indoor spraying and nets is often missed. The researchers concluded that future efforts must include a better understanding of human behavior and the development of new tools that protect people when they are outdoors. They recommend that health campaigns focus on the specific hours when people are outside, encouraging the use of nets even when sleeping outdoors and improving ventilation to make staying inside more comfortable. Additionally, they suggest targeting the mosquito larvae in breeding sites, a method that does not depend on where people sleep at night. By aligning control strategies with the actual rhythms of daily life, rather than assuming everyone stays indoors, health officials can better close the gaps that allow malaria to persist.