Transmission of drug-resistant Mycobacterium tuberculosis isolates between Finnish- and foreign-born patients, 2014-2021: a molecular epidemiological study

Abstract Background Data on the molecular epidemiological characteristics and transmission of drug-resistant Mycobacterium tuberculosis (MTB) isolates in low-incidence settings with immigration from high-incidence settings are limited. Method We included 101 drug-resistant MTB isolates with whole-genome sequencing data isolated in Finland between 2014 and 2021. Mutations associated with resistance to first- and second-line drugs were identified. Potential transmission clusters were identified using a threshold of 12 single-nucleotide polymorphisms (SNPs). Highly related clusters were identified using a threshold of 5 SNPs. Result Of the 101 drug-resistant MTB isolates, 29 (28.7%) isolates were from Finnish-born persons and 72 (71.3%) were from foreign-born persons. The proportion of foreign-born persons with multidrug-resistant (MDR) MTB (25/72, 34.7%) was higher than that in Finnish-born persons (6/29, 20.7%). The most common mutation associated with resistance to INH and RIF was katG Ser315Thr (67/83, 80.7%) and rpoB Ser450Leu (29/35, 82.9%), respectively. Lineage 4 (36/101, 35.6%) and lineage 2 (35/101, 34.6%) were prevalent lineages. A total of 16 (15.8%) isolates were classified into 7 potential transmission clusters (≤ 12 SNPs). Furthermore, one highly related cluster (≤ 5 SNPs) was identified, including one MDR isolate from a Finnish-born person and another MDR isolate from a person born in eastern Europe. Conclusion Transmission of drug-resistant MTB isolates between native and foreign-born persons is limited in Finland. Monitoring transmission dynamics of drug-resistant TB is of importance to inform tuberculosis management and control in low-incidence settings with increasing immigration.