A cluster of six respiratory cultures positive for Mycobacterium xenopi –Clinical characteristics and genomic characterization

Mycobacterium xenopi is a slow growing non-tuberculous mycobacterium (NTM) isolated from water systems and has been associated with pseudo-outbreaks and pulmonary infections in humans. We observed a cluster of six respiratory cultures positive for M. xenopi within a six-month period at our institution, approximately double our normal isolation rate of this organism. Only three of the six cases met clinical, radiographic, and microbiologic criteria for NTM infection. An investigation led by our hospital's Healthcare Epidemiology and Infection Program found no epidemiologic link between the six patients. Three isolates underwent whole-genome sequencing (WGS) and phylogenetic analysis confirmed they were non-clonal. In vitro susceptibility data found the isolates were sensitive to macrolides, moxifloxacin, and rifabutin. Our findings suggest that isolation of M. xenopi from pulmonary specimens may be increasing, further defines the genomic population structure of this potentially emerging infection, and establishes WGS as a useful tool for outbreak investigation strain typing.