Continued Upward Trend in Non-Tuberculous Mycobacteria Isolation over 13 Years in a Tertiary Care Hospital in Korea

PURPOSE: Despite decreased prevalence of tuberculosis, the incidence of the diseases associated with nontuberculous mycobacteria (NTM) has been increasing in South Korea and around the world. The present retrospective study was conducted to determine longitudinal changes in the epidemiology and distribution of NTM over 13 years at a tertiary care hospital in Korea. MATERIALS AND METHODS: We retrospectively analyzed data on Mycobacterium species over 13 years (January 2007 to December 2019) by utilizing the laboratory information system. Mycobacterium species were identified using biochemical tests and PCR-restriction fragment length polymorphism and Mycobacteria GenoBlot assays. RESULTS: After excluding duplicates from the initial pool of 17996 mycobacterial isolates, 7674 strains were analyzed and 2984 (38.9%) NTM were isolated. The proportion of NTM continuously increased over the 13-year period, from 17.0% in 2007 to 57.5% in 2019. Among the NTM isolates, the most common species were Mycobacterium intracellulare (50.6%), M. avium (18.3%), M. fortuitumcomplex (4.9%), M. abscessus (4.5%), M. gordonae (3.3%), M. kansasii (1.1%), M. chelonae (1.0%), and M. massiliense (0.9%). In patients over the age of 70 years, the proportion of NTM among the isolates increased from 26.6% in 2007 to 62.0% in 2019, and that of M. intracellulare isolates among the NTM increased from 13.9% (11/79) in 2007 to 37.4% (175/468) in 2019. CONCLUSION: The number of NTM isolates continuously increased over the study period, and the increase in the proportion of M.intracellulare in patients aged over 70 years was notable.