Phylogeography and transmission of M. tuberculosis in Moldova

Background The incidence of multidrug-resistant tuberculosis (MDR-TB) remains critically high in countries of the former Soviet Union, where >20% of new cases and >50% of previously-treated cases have resistance to rifampin and isoniazid. Transmission of resistant strains, as opposed to resistance selected through inadequate treatment of drug-susceptible TB, is the main driver of incident MDR-TB in these countries. Methods We conducted a prospective, genomic analysis of all culture-positive TB cases diagnosed in 2018 and 2019 in the Republic of Moldova. We used phylogenetic methods to identify putative transmission clusters; spatial and demographic data were analyzed to further describe local transmission of M. tuberculosis . Results Of 2236 participants, 779 (36%) had MDR-TB, of whom 386 (50%) had never been treated previously for TB. 92% of MDR M. tuberculosis strains belonged to putative transmission clusters. Phylogenetic reconstruction identified three large clades that were comprised nearly uniformly of MDR-TB; two of these clades were of Beijing lineage and one of Ural lineage, and each had additional distinct clade-specific second-line drug resistance mutations and geographic distributions. Spatial and temporal proximity between pairs of cases within a cluster was associated with greater genomic similarity. Conclusions The MDR-TB epidemic in Moldova is the result of local transmission of multiple M. tuberculosis strains, including distinct clades of highly drug-resistant M. tuberculosis with varying geographic distributions and drug resistance profiles. This study demonstrates the role of comprehensive genomic surveillance for understanding the transmission of M. tuberculosis and highlights the urgency of interventions to interrupt transmission of highly drug-resistant M. tuberculosis .