P063

1:McGill University; 2:Research Institute of the McGill University Health Centre; 3:Vietnam National University; 4:University of Sydney; 5:University of Melbourne; 6:Woolcock Institute of Medical Research

Vietnam is a high-burden country of Rifampicin-Resistant/multidrug resistant TB (RR/MDR-TB). Three dominating lineages are endemic to Vietnam, providing a unique Mycobacterium tuberculosis (Mtb) ecological setting to study drug resistance evolution and the efficacy of chemotherapy.

Using isolates collected from the VQUIN trial, we conducted a descriptive analysis of RR-TB isolates across Vietnam. We genotyped 255 Mtb genomes from 9 cities/districts representing north, central, and south Vietnam. Clinical isolates were sequenced on the Illumina Novaseq6000 system and aligned to the reference H37Rv genome for variant calling using Snippy. A maximum-likelihood tree was constructed with IQTREE, annotated by lineage and drug-resistance using TB-Profiler, and visualized using iTOL.

RR-Mtb strains were lineage 1 (20, 8%), lineage 2 (226, 88%), and lineage 4 (9, 4%). We found that the positive-predictive value of Xpert for WGS-confirmed RR and MDR was 96.5% and 92.5% respectively. Overall, 97% of all RR-Mtb strains in Vietnam were resistant to at least one other anti-mycobacterial drug. One case of BDQ resistance was detected, while no cases of resistance to pretomanid and linezolid was detected. Relevant to the intervention, 20% of RR-TB strains were fluoroquinolone resistant, with no XDR-TB strains detected (RR + resistance to fluroquinolones and bedaquiline and/or linezolid)

In summary, Lineage 2 was the dominant lineage in RR-TB isolates across Vietnam, consistent with the literature, but there were also lineage 1 and lineage 4 isolates.  A high rate of secondary resistance risks complicating the prevention and treatment of drug-resistant TB.