To better understand behavioural factors that might modify the risk of malaria during travel, a cohort of individuals living in Tororo under highly effective malaria control were assessed. Overall, LLIN use in travellers was low, and participants were less likely to use LLINs when they travelled than when at home. However, this finding was true only for women, and adults. Factors associated with higher LLIN use while travelling included travel to non-IRS districts, and travelling for more than one week, suggesting that perceived risk of malaria may influence the decision to sleep under an LLIN while away from home.
Travel has been identified as a risk factor for malaria across Africa [11, 15, 19, 30, 31]. In Uganda, a study conducted at three sites of varied malaria transmission demonstrated that the incidence of malaria in travellers was over three times higher in the 60 days after overnight travel compared to the 60 days before travelling . Another study in western Uganda found that travelling within the previous 4 weeks from highland areas with low malaria transmission to higher transmission areas was strongly associated with increased malaria risk . Two studies conducted on Bioko Island, Equatorial Guinea, demonstrated that island residents who travelled to the mainland were at increased risk of malaria infection [19, 30]. A survey of Bioko island travellers found that malaria prevalence was significantly higher in passengers returning to the island from the mainland compared to those departing the island . The odds of malaria among Bioko Island residents who travelled was significantly higher than in non-travellers, suggesting that imported malaria cases contributed to the sustained transmission of malaria on the island . Similarly, a study in northern Ethiopia found that travel from high-altitude (low transmission) villages to other areas within the previous month was associated with increased odds of malaria . This evidence suggests that travel within Africa is a risk factor for malaria infection. However, behavioural factors associated with travel that might increase exposure to mosquito vectors, and thus malaria infection, have been less well-explored.
There are several potential reasons why people may be at increased risk of malaria during travel. In this study, gender differences in LLIN use while travelling were observed. Women were less likely to use LLINs when travelling than at home, but this was not true for men. Interestingly, women reported using LLINs more often than men when at home; however, when travelling, the opposite was true. This suggests that at home, women may be more aware of the importance of sleeping under LLINs to protect against malaria, perhaps reflecting routine distribution of LLINs at antenatal clinics and targeted campaigns to increase LLIN use among pregnant women [32–34]. When travelling, women may either lack LLINs or the agency to use them, particularly when visiting the home of a friend or relative.
Individuals who travelled to non-IRS districts and those who travelled for more than 7 days were more likely to use LLINs. These findings suggest that the decision to use LLINs may be influenced by destination or duration of travel and the individuals’ perceptions of malaria risk. Indeed, perceptions of malaria risk have been shown to influence the use of LLINs when people travel . In south-eastern Tanzania, in-depth interviews were used to assess perceptions of malaria risk during outdoor and indoor activities. In this study, participants believed that outdoor activities such as fishing in the river late at night, travelling to farms overnight, and attending parties and funerals held at night, all increased their risk of malaria infection. For situations where use of LLINs was not feasible, participants believed that alternative malaria prevention approaches, including use of mosquito repellents and chemoprophylaxis, were needed.
LLINs are known to reduce malaria morbidity and mortality and are widely used for vector control in Africa , but achieving high adherence to LLINs, even at home, is challenging. In this study, just over half of cohort participants who travelled slept under LLINs when at home, despite universal access. Many barriers to LLIN use have been described, including many household members [36, 37], lack of space to hang LLINs , lower socioeconomic status, and time since the last LLINs distribution . In this study setting, where malaria transmission dropped substantially, individuals may have felt that it was no longer necessary to use their LLINs [5, 28]. During travel, a possible barrier to LLIN adherence is limited availability of LLINs to use away from home. Mass distribution of LLINs in Uganda follows WHO guidelines, which recommend distributing one LLIN for every two household residents . This may leave no spare LLINs for visitors, or for carrying during travel. In this study, other factors that may have contributed to limited use of LLINs during travel include social barriers, such as attending a funeral or wedding where individuals are expected to stay outdoors all night, or fear of appearing rude or disrespectful during communal gatherings . These factors should be considered when designing strategies to increase LLIN adherence in travellers.
A strength of this study is that behaviours at home and during travel within the same individuals were prospectively compared, minimizing the potential for confounding. Similar studies have only assessed malaria-relevant behaviours while travelling, or at home, but not both [23, 41, 42]. A study conducted in south-eastern Tanzania evaluated human behaviour of participants at home . The study found that a high proportion of participants (75%) stayed outdoors in the evenings (between 6 pm and 9 pm), resulting in exposure to malaria vectors before going to bed. Another study carried out in the Kilombero Valley of Tanzania from November 2015 to March 2016, assessed patterns of behaviour only when travelling, and demonstrated that when individuals travelled for religious, cultural and social gatherings, they stayed outdoors at night till dawn . Previous studies in Uganda that have assessed travel and malaria risk also examined behavioural factors during travel, such as use of LLINs [16, 17]. However, differences in behaviour while travelling versus at home were not explored. The findings from this study suggest that a better understanding of circumstances leading to lower use of LLINs when travelling may be important in guiding malaria prevention measures.
This study had several limitations. First, data on behavioural factors during travel could have been subject to recall bias. However, questionnaires were administered within 4 weeks following travel, and adherence to LLINs at home was assessed every two weeks by home visits, to closely evaluate the relationship between behaviours at home and when travelling. Second, the study was conducted in rural Tororo, and few individuals travelled outside of the district. Thus, results may not be generalisable to other settings. Lastly, intensive malaria control with IRS and LLINs resulted in few malaria cases in Tororo. Thus, it was not possible to directly measure the association between behaviours and malaria risk.