Transmission of rifampicin-resistant tuberculosis in Ho Chi Minh City, Viet Nam: a prospective genomic epidemiology study

Background Rifampicin-resistant tuberculosis (RR-TB) is a major threat to public health in Viet Nam, with nearly 10,000 incident cases estimated annually. It is uncertain whether these cases are driven by transmission of resistant strains or de novo resistance acquisition during treatment. Methods We undertook dense, city-wide sampling of adults newly diagnosed with pulmonary RR-TB in Ho Chi Minh City, Viet Nam's largest city, between March 2020 and April 2024. Participants provided sputum for culture and whole-genome sequencing (WGS), and demographic and clinical data were collected at enrolment. Phylogenetic analyses were combined with clinical histories to infer transmitted versus acquired rifampicin resistance. Estimates were corrected for sampling coverage using simulation-extrapolation (SIMEX). Temporal emergence of rifampicin resistance was reconstructed by lineage using Bayesian phylogenetic dating, and the geographic and demographic structure of transmission networks was assessed using geocoded residential data and commute time-based analyses. Findings Among 2,319 RR-TB cases diagnosed during the study period, 1,491 (64%) isolates were successfully sequenced. After accounting for sampling and phylogenetic uncertainty, we estimated that between 72% and 87% of all RR-TB arose through transmission of already-resistant strains with the remainder due to de novo acquired resistance. Bayesian dating analyses revealed that resistance emergence events occurred repeatedly from the 1980s to the present, with early events seeding long-lived, city-wide transmission networks. Transmission networks were geographically dispersed across the city, with limited household clustering, and only weakly structured by host demographics, consistent with diffuse, city-wide transmission rather than localised or assortative spread. Interpretation RR-TB in Ho Chi Minh City is driven predominantly by ongoing transmission, but a substantial minority of cases arise from newly acquired resistance. Alongside promoting early diagnosis and treatment to interrupt transmission, the main drivers of acquired resistance need to be identified to control RR-TB.