Epidemiological trends and clinical relevance of nontuberculous mycobacterial pulmonary disease in a referral hospital in Japan, 2017-2021

Background: Epidemiological trends and clinical relevance of NTM species in Japan following the adoption of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry remain unclear. Methods: We analyzed the results of mycobacterial culture tests of respiratory specimens collected between January 2017 and December 2021. We assessed the clinical relevance of NTM species by analyzing the proportion of patients diagnosed with NTM pulmonary infection (NTM-PI). We illustrated the incidence and clinical relevance of each NTM species using a two-dimensional scatter plot. Medical chart review and radiological analysis were also performed for less common species. Results: Among 65,368 respiratory specimens tested for acid-fast bacilli, NTM were identified in 12,802 specimens from 3177 patients. The number of incident cases with NTM-PI has continued to increase. Notably, the number of incident cases with M. abscessus species (MABS) was continuously increasing and accounted for 10.6% of all incident cases with NTM-PI. The clinical relevance of the common NTM species, M. avium complex, MABS and M. kansasii, ranged from 57 to 72%. Seven other species exhibited a higher clinical relevance than these common NTM species, with M. shinjukuense (100%) having the highest clinical relevance. On the other hand, 11 species, including M. fortuitum (32.4%), M. xenopi (20.0%), and M. gordonae (22.9%), showed clinical relevance below 50%. Conclusions: The present study clarified the incidence and clinical relevance of NTM species using a two-dimensional scatter plot, which could serve as a useful tool for clinical decision-making and future epidemiological research.