Nosocomial Mycobacterium lentiflavum colonization and infection cluster at a Japanese tertiary care center: report of an outbreak/pseudo-outbreak investigation

Objective: Mycobacterium lentiflavum is a rare, non-tuberculous mycobacterium (NTM) which is implicated in some cases of active, pulmonary non-tuberculous mycobacterial disease. The outbreak of NTM in nosocomial settings occasionally occurs and outbreak investigation with implementation of concurrent countermeasure is essential. Design: Outbreak investigation. Setting: A tertiary care medical center. Patients and participants: Hospitalized patients during the outbreak period. Results: In April 2024, a cluster of patients with Mycobacterium lentiflavum–positive sputum cultures, presumed to be due to nosocomial transmission, was identified at the study center. A retrospective review of cases dating back to February 2023 revealed 27 patients with M. lentiflavum infection whose isolates had initially not been speciated. According to the American Thoracic Society (ATS) criteria for diagnosing pulmonary non-tuberculous mycobacterial (NTM) disease, two of these patients met the criteria for active disease. Multi-locus sequence typing of 12 isolates demonstrated 100% clonality, indicating a common source. A concurrent outbreak investigation identified contaminated faucet aerators in hospital wards as the likely source of transmission. All faucet aerators and caps were manually cleaned and disinfected using liquid sodium hypochlorite, after which no further cases were detected. Conclusion: The present study described a nosocomial cluster of M. lentiflavum colonization and infections at a tertiary care center, with contaminated faucet aerators identified as the likely source. Prompt identification of such NTM clusters in healthcare settings is essential to initiate timely treatment and prevent further transmission.