Recent overnight travel and the risk of malaria: case-control and prospective cohort studies in Uganda

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 15 years (33.9% travel vs 61.3% home, RR 0.55, 95% CI 0.41-0.74, p