Clinical characteristics and diagnostic challenges of pulmonary Mycobacterium lentiflavum infection in adults

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Background: Pulmonary infection caused by Mycobacterium lentiflavum (PMLF) is a rare form of NTM disease that remains underrecognized and requires further investigation. Additionally, M. lentiflavum may have been misidentified as M. intracellulare in the COBAS TaqMan MAI test. While the introduction of MALDI-TOF MS has likely reduced such misidentifications, earlier cases may have been overlooked. Methods: We reviewed medical records of non-HIV adult patients with PMLF at the National Center for Global Health and Medicine from July 2015 to June 2021. Among 1,191 samples initially identified as M. intracellulare by the COBAS TaqMan MAI test, 187 patients had ≥2 positive cultures. As part of an interim analysis, whole genome sequencing was performed for 156 samples from 99 patients. Cases meeting the ATS/IDSA diagnostic criteria were included. Results: Among 42 individuals with ≥2 positive cultures for M. lentiflavum, 37 were considered transiently colonized cases, leaving 5 clinically significant PMLF cases. The median age was 69 years (range: 35–88), and 80.0% were female. Sputum smear tests were positive in three cases (60%). One patient had a history of pulmonary tuberculosis. All patients had a nodular/bronchiectatic (NB) pattern on chest CT. One patient received antimycobacterial combination therapy. The clinical course was generally indolent, and no deaths occurred. Conclusions: PMLF predominantly affects older females, presents with an NB pattern on chest CT, and follows a generally non-aggressive course. Increased awareness is essential, particularly for cases diagnosed before the widespread adoption of MALDI-TOF MS.

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