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 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-July 2021) and implemented an initial intervention.In Phase 2 (November 2021-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-December 2022).However, MAM was isolated from the environment during follow-up surveys.A total of 52 MAM isolates were analyzed, including 11 clinical isolates (one from M1-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, J o u r n a l P r e -p r o o f formed the hub of the inter-cluster 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.
Yoshida et al. (Sun,) studied this question.