Outcomes of non-tuberculous mycobacterial infection of the bone, joint and soft tissue: a seven-year multicentre retrospective study

PURPOSE: Extrapulmonary nontuberculous mycobacterial (EPNTM) infections of bone, joint, and soft tissue are difficult to treat and lack species-specific outcome data. We sought to describe antimicrobial regimens and surgical management by Mycobacterium spp. and to identify predictors of a clinical cure within 12 months in this adult cohort with EPNTM. METHODS: We conducted a multicentre retrospective cohort study across five tertiary hospitals in Australia and New Zealand 2014-2020. Adults with culture-confirmed EPNTM infection from sterile or intraoperative specimens were included. Primary outcome was clinical cure at 12 months. Secondary outcomes included relapse, drug toxicity and host factors. RESULTS: Among 107 patients, six species groups were identified, most commonly M. abscessus complex (n = 26, 25%), Mycobacterium marinum (n = 25, 24%), and M. fortuitum complex (n = 24, 23%). Clinical cure within 12 months differed significantly by species, with high cure proportions for M. abscessus complex (n = 22, 92%) in surgically accessible infections and lower cure rates for M. chelonae (n = 6, 60%) and amalgamated slow growing mycobacteria (n = 4, 36%). Younger age (median 47 vs. 60 years, p = 0.006) and Mycobacterium spp. was associated with cure whereas antimicrobial class and surgical intervention were not. Of antibiotic classes used, only macrolide duration was associated with cure. Relapse was uncommon (8%) and occurred predominantly in immunosuppressed patients. CONCLUSIONS: This first multicentre Australasian cohort demonstrates substantial species-specific variation in outcomes of EPNTM osteoarticular and soft-tissue infections. This study highlights the need for species-specific management pathways and prospective studies.