P064

1:Latvian Biomedical Research and Study Centre; 2:Riga Stradins University; 3:Riga East Clinical University Hospital, Centre of Tuberculosis and Lung Diseases

Tuberculosis (TB) remains a public health challenge in Latvia, a low-to-moderate TB incidence country. However, data on local transmission dynamics, particularly in regions outside the capital Riga, are limited. Herein, we analysed all Mycobacterium tuberculosis (Mtb) isolates obtained from patients with TB diagnosed in 2016-2017 and who resided in Eastern Latvia region, to gain insights into TB transmission patterns. Using Illumina technology, Mtb isolates from 144 patients with active TB residing in three cities and 27 counties were subjected to whole-genome sequencing (WGS). WGS-based genotyping via TB-Profiler software revealed three Mtb lineages and 10 sub-lineages, with sub-lineages 4.3.3 (LAM) and 4.8 (mainly T) being equally most prevalent (27%, 39/144). Based on phenotypic drug susceptibility testing (DST) and WGS-based DST interpreted using the latest WHO Mtb genetic variant catalogue, 31 isolates (22%) were resistant to at least one anti-TB drug; most were classified as isoniazid-resistant (11%, 16/144). A 5-SNV threshold was applied to identify recent transmission events and clusters. In total, 12 recent transmission events and six clusters (3-11 patients) were detected, involving 55 patients (38%) residing in the same or nearby cities or counties. As anticipated, most closely genetically linked isolates belonged to sub-lineages 4.3.3 (13%, 18/144) and 4.8 (10%, 15/144); however, the largest cluster (11 patients) consisted of isolates from sub-lineage 4.1.2 (Euro-American). Notably, only one cluster and one recent transmission event involved drug-resistant isolates. To conclude, local TB transmission in Eastern Latvia appears limited, suggesting many patients may have acquired the infection outside the studied region.