Cohort Profile: Migrant Health Follow-Up Study (MHFUS) of internal migration in South Africa

Why was the cohort set up?Changes in population distribution through migration and urbanization are associated with transitions in health exposure regimens and health outcomes. 1However, our understanding of these links remains limited.South Africa's disease burden is among the highest of the world's middle-income countries, with high prevalence of infectious disease (ID) and non-communicable disease (NCD), 2,3 exacerbated by inadequate monitoring and availability of health information and services. 4 Internal mobility in South Africa is high as people move to urban areas in search of work, often on a temporary basis.These patterns of mobility are rooted in the apartheid legacy of circular and temporary migration between rural and urban areas. [5]][7] The Migrant Health Follow-Up Study (MHFUS) responds to the need to fill this knowledge gap.The MHFUS, funded by the National Institutes of Health, USA, began recruitment in 2017 in the Bushbuckridge district, Mpumalanga Province, in South Africa's northeast.We aim specifically to understand whether and how internal migration and urbanization affect NCD and ID risk, and whether migration compromises treatment continuity.By examining migration dynamics at high spatial and temporal resolutions, with attention to selection and heterogeneity, we aim to assess these Key Features� The Migrant Health Follow-Up Study (MHFUS) was established to address a knowledge gap about the consequences of migration and urbanization for individual health in a dynamic socioeconomic transition setting in South Africa.� The cohort is based on a simple random sample of 3800 18-40-year-olds selected from the Agincourt Health and socio-Demographic Surveillance System (HDSS) in 2017, and consists of both highly mobile internal migrants and Agincourt HDSS residents remaining in their rural origin.� The cohort has thus far been followed for four study waves between 2018 and 2022, with information on education, employment, migration, household composition, health (including general health, chronic conditions, HIV, sleep), health service use and diet collected in all waves; biometric and anthropometric measures collected during the face-to-face interview rounds in Waves 1 and 4 (interviews were administered via telephone in Waves 2 and 3).� The study has achieved exceptional rates of cohort retention, with 98% of Wave 1 participants re-interviewed in Wave 4 (n ¼ 3039).