Title : Transmission of drug-resistant mycobacterium tuberculosis isolates between Finnish- and foreign-born cases, 2014-2021: A molecular epidemiological study
Abstract:
Background: Data on the molecular epidemiological characteristics and transmission of drug-resistant Mycobacterium tuberculosis (MTB) in low-incidence settings with immigration from high-incidence settings is limited.
Method: We included 115 drug-resistant (DR) MTB isolates with whole-genome sequencing data isolated in Finland between 2014 and 2021. 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 115 DR MTB isolates, 31 (27.0%) isolates were from Finnish-born cases and 84 (73.0%) were from foreign-born cases. The proportion of multidrug-resistant (MDR) MTB isolates (30/84, 35.7%) from foreign-born cases was higher than that of MDR MTB isolates from Finnish-born cases (8/31, 25.8%). The 115 DR MTB isolates were classified into four lineages, including lineage 1/Indo-Oceanic, lineage 2/East-Asian, lineage 3/East-African-Indian, and lineage 4/Euro-American. The lineage 2 (40/115, 34.8%) and lineage 4 (40/115, 34.8%) were prevalent lineages. The lineage diversity of DR MTB isolates was significantly different by regions of birth. DR MTB isolates from Finnish-born cases were classified into four lineages, with a dominant lineage 4. Isolates from Asia-born cases were mainly lineage 1, while most isolates from eastern European-born and sub-Saharan African-born cases were lineage 2 and lineage 3/Delhi-CSA, respectively. A total of 25 (21.7%) isolates were classified into eight potential transmission clusters (≤12 SNPs). The largest potential transmission cluster included nine lineage 3 isolates from patients notified between 2017 and 2020 and all, except one with an unknown country of birth, originating from sub-Saharan Africa. Within this cluster, three isolates from Eritrean-born patients and one isolate from Ethiopian-born patient were highly related. Four clustered isolates were from Finnish born patients and three of them were closely related to foreign-born patient isolates and one was possibly related. Two MDR-TB clusters were found, both consisted of two isolates of lineage 2 and 4, respectively, from foreign-born patients.
Conclusion: Transmission of drug-resistant MTB isolates between Finnish- and foreign-born persons is uncommon. Monitoring transmission dynamics of drug-resistant TB is of importance to inform tuberculosis management and control in low-incidence settings with increasing immigration.
