OR08

1:International Reference Laboratory of Mycobacteriology, Statens Serum Institut, 2300 Copenhagen S, Denmark..; 2:Mycobacteriology/Institute of Tropical Medicine (ITM), Antwerp, Belgium.; 3:Department of Biosciences, Nottingham Trent University, Nottingham, UK.; 4:Department of Biotechnology and Biomedicine, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.; 5:Global Health Section, Department of Public Health, University of Copenhagen, 1353 Copenhagen K, Denmark.

The prevalence of nontuberculous mycobacteria (NTM) disease continue to rise and remain a challenge worldwide. Taking advantage of the International Reference Laboratory of Mycobacteriology (IRLM)´s collection of freeze-dried mycobacterial isolates, we investigated changes in NTM epidemiology and species distribution in humans over the past seven decades. This study compares historical NTM-designated isolates (n=666) from human samples (1948–1978) to contemporary (2013-2022) NTM isolates (n=1820) identified in routine diagnostics. Survey of patient metadata showed median ages of 54.9 and 57.4 year for the historical and contemporary isolates, respectively. Species identification was performed using GenoType CM assay, which differentiates among the most common mycobacteria in clinical settings today. For historical isolates, 16 distinct species categories were identified, with the majority remaining unclassified, designated as M. species (32.13%). In contrast, recent isolates were dominated by M. avium (39.62%), while M. species accounted only for 7.8%. Among the most abundant characterizations, M. avium and M. abscessus showed largest changes and increase in prevalence over time. Further species determination by whole-genome sequencing was performed for most historical isolates characterised as M. species, revealing a number of species not usually encountered in diagnostic settings today.  

These findings suggest significant changes in the mycobacterial species involved in NTM infections in Denmark over the past seven decades, likely influenced by broader societal and environmental factors. However, definitive conclusions regarding changes in NTM epidemiology cannot be made due to limited information about the criteria for storing the historical isolates.