Setting: Shanghai is a mega city where 39% of the population comprises internal migrants.
Objective: To examine the different roles played by migrants and permanent residents in the transmission of multidrug-resistant tuberculosis (MDR-TB).
Design: We conducted a population-based cohort study to assess MDR-TB transmission in Shanghai between 1 January 2009 and 31 December 2012 using genotyping and geospatial analyses.
Results: A total of 367 MDR-TB cases formed the study cohort. Significant differences between MDR-TB cases who were internal migrants and those who were permanent residents were found with regard to age, sex, region, genetic characteristics and treatment outcomes. Permanent residents had a higher transmission rate than internal migrants (OR 3.36, 95%CI 1.86-6.09). Permanent residents and genotypic clustering cases had similar clusters in central downtown and some parts of suburban areas. Most of the clusters of internal migrants were found in rural areas bordering suburban areas. Clusters of genotypic non-clustering cases showed patterns that closely matched those of internal migrants, suggesting acquired drug resistance in migrants.
Conclusion: In Shanghai, permanent residents were significantly associated with recent transmission of MDR-TB in central downtown areas. Clustered cases of internal migrants in rural areas were most likely to have contracted MDR-TB through acquired resistance.