Internal migrants as drivers of long-distance cross-regional transmission of tuberculosis in China

Objectives Internal migrants in China frequently travel between their hometowns and the cities where they work, creating ample opportunities for cross-regional transmission of tuberculosis (TB). The aim of this study was to explore the role of internal migrants in transmitting TB across different regions and the contribution of cross-region transmission to China's TB burden. Methods The study included a total of 8664 patients with TB and their Mycobacterium tuberculosis isolates, collected from two large cities and three rural regions. Genomic clusters were defined as having a genomic distance of <= 12-single nucleotide polymorphisms. Cross-regional clusters were defined as clusters containing patients from at least two regions, indicative of cross-regional transmission. Results A total of 2403 clustered cases (27.7%) were grouped into 845 clusters, of which 142 (16.8%) were cross-regional. An increased risk for cross-regional transmission was found for internal migrants (adjusted OR (aOR), 1.45; 95% CI, 1.13-1.87), individuals aged <55 years (aOR, 2.73; 95% CI, 1.81-4.13), and housekeepers/factory workers (aOR, 1.16; 95% CI, 0.90-1.50). Among 200 cross-regional transmission events identified by transmission inference, 96 occurred between urban patients, 98 between urban and rural patients, and only six between rural patients. Notably, 93.5% (187/200) of cross-regional transmission events involved internal migrants. Epidemiological data showed that just 5.5% of cross-regional transmission events involved patients from the same township or neighbouring counties, where the transmission likely occurred. Discussion The mobility of the internal migrant population appears to be responsible for most cross-regional transmission of TB in China. The magnitude and dynamics of cross-regional transmission should be addressed in future strategies to reduce the incidence of TB in China. Meng Li, Clin Microbiol Infect 2025;31:71 (c) 2024 European Society of Clinical Microbiology and Infectious Diseases. Published by Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.