Fomite transmission of Mycobacterium abscessus between severely disabled patients

OBJECTIVES: We aimed to investigate a nosocomial outbreak of Mycobacterium abscessus subspecies massiliense (MAM) and to track its transmission route via genomic analyses and environmental surveys at a hospital in Osaka, Japan. The outbreak was initially detected in two patients (M1 and M2) with severe disability in 2020 and then expanded to five other patients (M3‒M7). METHODS: The 34-month observation period was divided into three phases separated by two interventions. Mycobacterial culture screening was performed for 294 clinical and environmental samples. We confirmed that five patients (M1‒M5) had infections in phase 1 (March 2020 to July 2021) and implemented an initial intervention. In phase 2 (November 2021 to May 2022), new patients (M6 and M7) were identified, wherein an environmental survey identified MAM strains, prompting a second intervention. No patients were identified in phase 3 (September to December 2022). However, MAM was isolated from the environment during follow-up surveys. A total of 52 MAM isolates were analysed, including 11 clinical isolates (one from M1 and M2 in each phase and one each from M3-M7) and 41 environmental isolates obtained from care gloves, medical devices, and room equipment surrounding patients. We sequenced the isolate genomes and identified 15 subclone clusters with a threshold of 24.5 single-nucleotide variants (SNVs). RESULTS: The overall SNV distribution of the clinical and environmental strains was within 61 SNVs, showing near-identical genomes. Clinical strains from patient M2 with persistent positivity were classified as the same subclone, with 0-6 SNVs. The isolate from a wagon brought into patient rooms showed the lowest number of SNVs (3-8) compared with isolates from M2. This subclone cluster, involving M2 and wagon isolates, formed the hub of the intercluster connection of 11 clusters comprising other clinical and environmental strains. CONCLUSIONS: M. abscessus could persist in dry environments and might be indirectly transmitted via fomites.