Abstract
In industrialized countries the majority of tuberculosis (TB) cases are linked to immigration. In Finland, most cases are still Finnish born but the number of foreign born cases is steadily increasing. In this 4-year population based study, the TB situation in Finland was characterized by a genotypic analysis of Mycobacterium tuberculosis isolates. A total of 1048 M. tuberculosis isolates (representing 99.4% of all culture positive cases) were analyzed by spoligotyping and MIRU. Spoligotype lineages belonging to the Euro-American family were predominant among the Finnish isolates, particularly T (n=346, 33.0%) and Haarlem (n=237, 22.6%) strains. The lineage signature was unknown for 130 (12.4%) isolates. Out of the 17 multi-drug resistant TB strains, 10 (58.8%) belonged to the Beijing lineage. In total, 23 new SIT designations were given and 51 orphan strains were found, of which 58 patterns were unique to Finland. Phylogeographical TB mapping as compared to neighboring countries showed that the population structure in Finland most closely resembled that observed in Sweden. By combining spoligotyping and MIRU results, 98 clusters comprising 355 isolates (33.9%) were found. Only 10 clusters contained both Finnish and foreign born cases. In conclusion, a large proportion of the M. tuberculosis isolates were from Finnish born elderly patients. Moreover, many previously unidentified spoligotype profiles and isolates belonging to unknown lineages were encountered.
Highlights
Mycobacterium tuberculosis isolates belonging to the Beijing genotype family [5]
This study provides an update of the molecular epidemiology of TB in Finland
The 4-year nationwide data showed that the majority of the TB cases were Finnish born and a large proportion was aged 65 or older
Summary
Mycobacterium tuberculosis isolates belonging to the Beijing genotype family [5]. M. tuberculosis isolates belonging to the Beijing lineage were infrequently encountered in Finland [9]. MDR-TB cases will most likely increase in Finland as well, because of the rapid spread of the Beijing lineage across Europe and increasing immigration to Finland. To better understand the current epidemiology of TB in a country with a history of high TB incidence, the aim of the study was to evaluate the current TB situation in Finland by genotypic characterization of M. tuberculosis complex isolates. Our first objective was to use the typing data to provide a general overview of the genotypes retrieved from TB cases in Finland, and compare the situation in Finland to our neighboring countries
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