Temporal trends and changing epidemiology of non-tuberculous mycobacteria over four decades: a retrospective laboratory-based study

Objectives The incidence of non-tuberculous mycobacteria (NTM) isolations has increased worldwide, although the relative contribution of demographic changes, increasing patient complexity, environmental factors, and advances in diagnostic techniques remains unclear. We aimed to describe long-term trends in NTM isolations and epidemiological changes. Methods We performed a retrospective study of NTM-positive clinical samples processed at a tertiary referral hospital in Barcelona between 1986 and 2021. Individual demographic and microbiological data were available until 2021, whereas only aggregate data on total samples processed and NTM-positive cultures were available for 2022–2023 and were used exclusively for temporal trend analyses. Trends were analysed using logistic regression, generalized additive models, and a one-breakpoint segmented logistic regression; evidence for a change in slope was formally assessed using the Davies test. Demographic characteristics, specimen type, and species distribution were compared between two periods (1998–2005 and 2014–2021). Results A total of 5,848 NTM-positive samples were identified. Among samples with available demographic data, 3,918 (66.9%) corresponded to male patients. Respiratory specimens accounted for 4,147 (70.9%) samples, whereas 426 (7.3%) were non-respiratory. Temporal trends showed a non-linear pattern. The segmented model estimated a change-point at 2017.5 (95% CI 2016.9–2018.2), with a marked increase thereafter (annual percent change 21.7%, 95% CI 18.6–24.8); the Davies test provided strong evidence of a change in slope (p<0.001). Species distribution changed significantly over time, partly reflecting improvements in microbiological identification. The Mycobacterium avium complex remained the most frequently isolated group, whereas M. kansasii and M. xenopi declined substantially. Compared with 1998–2005, patients in 2014–2021 were older (mean age 60 vs. 56 years, p<0.001) and more frequently female (41.9% vs. 28.3%, p<0.001). Conclusions Two distinct periods of increased NTM isolation were observed over the study period, with the most recent acceleration occurring around 2017–2018. This increase occurred alongside important changes in species distribution and patient demographics. These findings highlight the evolving epidemiology of NTM and support the need for enhanced surveillance systems and improved differentiation between colonization and active disease.