Do adult health outcomes in urban population reflect local health risk? A matched cohort analysis of migration effects in Ouagadougou, Burkina Faso

BACKGROUND: Selective migration may affect health indicators in both urban and rural areas. Sub-Saharan African urban areas show evidence of both negative and positive selection on health status at outmigration. Health outcomes as measured in urban populations may not reflect local health risks and access to health services. METHODS: Using the Ouagadougou Health and Demographic Surveillance System and a migrant follow-up survey, we measured differences in health between matched non-migrants and outmigrants. We applied Cox and competing risks models on migration and death. RESULTS: Controlling for premigration health status, migrants who moved out of Ouagadougou have higher mortality (HR 3.24, 95% CI 1.23 to 8.58) than non-migrants and migrants moving to other Ouagadougou areas. However, these effects vanish in the matched sample controlling for all interactions between death determinants. These and other results show little evidence that migration led to higher mortality or worse health. CONCLUSIONS: Health outcomes as measured in Ouagadougou population do reflect local health risks and access to health services despite high migration intensity. However, neither the hypothesis of effect of health on migration nor the hypothesis of negative effect of migration on health or survival was confirmed.