Incidence and clinical significance of non-tuberculous mycobacteria among migrants in Denmark: a nationwide register-based cohort study from 1991 through 2021

BACKGROUND: There is limited knowledge about non-tuberculous mycobacteria (NTM) infections in migrants. We aimed to assess the incidence and clinical significance of NTM among migrants in Denmark.

METHOD: Nationwide register-based cohort study of migrants with a positive NTM culture in Denmark from 1991 through 2021, stratified by patient demographics, disease localisation, species, and clinical significance.

RESULTS: 433 migrants had a positive NTM culture, resulting in an overall incidence rate (IR) of 3.7 (95%CI 3.3-4.0) per 100,000 migrants. Overall NTM IRs for definite disease were 1.0 (95%CI 0.9-1.2), possible disease 1.0 (95%CI 0.8-1.2), and isolation 1.7 (95%CI 1.4-1.9) per 100,000 migrants. Migrants had considerably higher age- and sex-adjusted NTM IRs of positive cultures (incidence rate ratio [IRR] = 2.1, 95%CI 1.9-2.3, p < 0.001), possible disease (IRR = 2.4, 95%CI 2.0-3.0, p < 0.001), and isolation (IRR = 4.6, 95%CI 3.9-5.4, p < 0.001) compared to Danish-born, but not of definite disease (IRR = 1.1, 95%CI 0.9-1.3, p = 0.562). IRs of migrants with positive NTM cultures did not increase over time (-0.8 %/year, p = 0.133).

CONCLUSIONS: Migrants have a higher, but stable, burden of NTM compared with Danish-born. The higher rates likely reflect that more specimens are examined for Mycobacterium tuberculosis. Microbiologically classified definite NTM disease is not substantially more common among migrants.