Maintaining community-based cohorts in sub-Saharan Africa: An evaluation of participant attrition in SchistoTrack

BackgroundUnderstanding participant attrition in longitudinal studies is essential for maintaining cohorts, establishing targeted interventions, and assessing potential biases introduced in study analyses. Yet, limited metrics, models, and long-term assessments exist for the evaluation of community-based cohorts in sub-Saharan Africa. MethodsWe prospectively assessed participant attrition in the SchistoTrack cohort. A total of 2844 individuals aged 5-92 years were examined from 1445 randomly sampled households across three rural Ugandan districts. Baseline data on sociodemographics, medical history, spatial factors, and clinical examinations were collected in 2022, with annual and seasonal follow-ups analysed to 2024. Profiles of attriters and rejoiners were established with logistic regressions, while the timing of the first attrition event was analysed in multinomial models. Annual community engagement was conducted. FindingsOverall attrition rates were stable across the years ranging from 21-24.8%. Attriter profiles were established within the first year, with only borderline significant factors identified. Home ownership, compared to renting was negatively related to attrition (0.773; CI 0.599-0.998). And, each additional household member reduced the likelihood of attrition (0.923; CI 0.863-0.987). Higher education was positively associated with attrition (1.077; CI 1.047-1.108). Fishermen were not more likely than other individuals to have an attrition event, either overall or seasonally. 40.1% (240/598) of participants who dropped out from the first major follow-up rejoined the study at the following timepoint. Schistosome infection and the need for schistosomiasis-related medical referrals were not associated with later attrition when compared to uninfected individuals and individuals with referrals for ancillary causes or no needed referral. Communicating clinical findings and adjusting incentives across the years did not negatively impact study participation. InterpretationBy providing metrics and models for tracking attrition, our attrition analysis framework can guide the design and evaluation of community-based cohorts in rural sub-Saharan Africa. What is already known on this topicParticipant attrition in longitudinal studies is common and, if not measured and accounted for, can lead to analytical biases and reduced statistical power to produce substandard study designs as well as reduced access to continued care for participants needing further treatment. What this study addsWe comprehensively tracked attrition in a large-scale prospective cohort (SchistoTrack). Attrition at the levels of the individuals, households, villages, and districts was examined in rural Uganda. We investigated a wide range of biomedical, social, spatial, and cultural factors, and developed generalisable procedures and metrics for examining attrition both temporally and seasonally in community-based studies in sub-Saharan Africa. How this study might affect research, practice or policyMore cohort studies urgently are needed in sub-Saharan African countries to understand disease development within these diverse populations. We provide a comprehensive framework to monitor and evaluate the impact of attrition to promote the successful maintenance of rigorous cohort studies. The attrition rates established here can also be used more widely to design effective participant sampling and sample size calculations across different epidemiological study designs.