Relationship between age, sex, geography and incidence of nontuberculous mycobacteria in Denmark from 1991 to 2022.

Objectives: We investigated age, sex and geographical differences in nontuberculous mycobacteria (NTM) incidence in Denmark. Methods: A nationwide register-based study of all patients with NTM isolates in Denmark from 1991 to 2022 based on centralised microbiological data from the International Reference Laboratory of Mycobacteriology, Statens Serum Institut, Copenhagen, Denmark. A Poisson regression model was used to calculate incidence rates (IRs) and rate ratios (IRRs). Results: 4123 patients had NTM isolated for the first time. Their median age was 59 years (interquartile range 33-72), which increased over time. Males were younger than females. The proportion of females increased significantly over time. The type of NTM and patient age were closely associated. Pulmonary NTM isolation was increasingly common with higher age, while extrapulmonary NTM isolation was mainly seen in small children. Pulmonary NTM IRs were almost twice as high for females in 2008-2022 compared to 1991-2007 (IRR 1.9, 95% CI 1.7-2.1, p<0.001), with increases mainly seen in older age groups. The increase was less pronounced for males (IRR 1.3, 95% CI 1.1-1.4, p<0.001). There were considerable geographical differences, with age- and sex-adjusted NTM IRs being 10-40% higher in countryside, provincial and catchment municipalities than in the capital. Conclusion: Age, sex and geography are essential determinants in NTM epidemiology. We found that rates of pulmonary NTM have been increasing, particularly in older females, while changes for males were less pronounced. Finally, we observed considerable geographical differences in NTM IRs in Denmark, with higher rates in less populated municipalities.