title: Recent overnight travel and the risk of malaria: case-control and prospective cohort studies in Uganda
Creators: name: Arinaitwe, E
Publisher: name: London School of Hygiene & Tropical Medicine
Year: 2021

description: Introduction: Travel is an underappreciated risk factor for malaria in residents of malaria-endemic countries. In Uganda, malaria transmission is heterogeneous, in part due to expansion of malaria control interventions and increased urbanization. As a result, individuals who travel may be at higher risk of malaria infection. However, our understanding of the association between travel and malaria infection in Uganda is limited. Methods: This thesis aimed to address this evidence gap through: 1) case-control study in urban Kampala, 2) cohort study in three sites of varied malaria transmission, and 3) cohort study in rural Tororo, which is under intense malaria control with indoor residual spraying (IRS). For the case control study, 5 controls were selected for every 2 cases, matching on age. Data were collected in July and August 2019 on recent overnight travel out of Kampala (past 60 days), destination and duration of travel, and behavioural factors, including sleeping under a long-lasting insecticidal net (LLIN) during travel. For the cohort study at three sites in Uganda (PRISM 1), information on overnight travel was collected between 2015 and 2016 from children aged 0.5-10 years and one adult living in 266 randomly selected households. Malaria, defined as fever with parasites detected by microscopy, was measured using passive surveillance. For the cohort in rural Tororo (PRISM 2), data on overnight travel and behaviour during travel were collected from residents of 80 households between 2017 and 2019. Behaviour while at home was assessed using a similar questionnaire during two-weekly home visits. Results: In the case-control study, 162 cases and 405 controls were enrolled. Overall, 158 (27.9%) participants reported recent overnight travel. Travellers were far more likely to be diagnosed with malaria than those who did not travel (80.4% vs 8.6%, odds ratio 58.9, 95% 4 confidence interval [CI] 23.1-150.1, p&lt;0.001); travelling to a non-IRS district, not using LLINs during travel, and engaging in outdoor activities were associated with increased odds of malaria. In the PRISM 1 cohort study, at least one overnight trip was reported by 120 of 906 (13.3%) participants. Among individuals who travelled, the incidence of malaria was higher in the first 60 days after travelling, compared to periods without recent travel at all sites (overall 1.15 vs 0.33 episodes per person-year, incidence rate ratio 3.53, 95% CI 1.85-6.73, p&lt;0.001). In the PRISM 2 cohort study, 527 participants were enrolled and 123 (23.2%) reported taking at least one overnight trip. Overall, participants were less likely to use LLINs when travelling than at home (41.0% vs. 56.2%, relative risk [RR] 0.73, 95% CI: 0.60-0.89, p=0.002). In the analysis adjusted for gender and age, significantly lower LLIN use during travel was found for female participants (38.8% when travelling vs 59.2% at home, risk ratio [RR] 0.66, 95% CI 0.52-0.83, p=0.001) but not for males (48.3% vs 46.6%, RR 0.96, 95% CI 0.67-1.40, p=0.85), and those &gt; 15 years (33.9% travel vs 61.3% home, RR 0.55, 95% CI 0.41-0.74, p&lt;0.001). Conclusions: Residents of malaria endemic countries who travel are a high-risk group that should be targeted for malaria prevention. For these travellers, personal protection measures, including sleeping under LLINs when traveling, application of creams or sprays to prevent outdoor mosquito bites, and administration of chemoprophylaxis, should be advocated.