Identification of Mycobacterium porcinum in patients with cystic Fibrosis: Pathogen or contaminant?

BACKGROUND: Mycobacterium porcinum is a non-tuberculous mycobacterium (NTM) identified in potable water. The identification and clinical impact of M. porcinum in patients with cystic fibrosis (CF) has not been described. In our institution, M. porcinum was isolated exclusively during hospitalization in a cluster of patients with CF. METHODS: Patients with CF who were hospitalized between September 2016 and September 2018 and could expectorate sputum were included, and samples were processed per institutional guidelines. Post-hospitalization and one-year clinical outcomes on those who isolated M. porcinum in respiratory cultures were reviewed. Whole genome sequencing was performed on M. porcinum isolates obtained from patients and environmental sources to identify source of acquisition. RESULTS: Review of 14 CF patients with 16 M. porcinum isolates revealed rapid time to culture positivity within 0.8 (0.04-8.0) days after admission. M. porcinum was isolated in teenagers and adults irrespective of baseline pulmonary function, body mass index, or CF genotype. Whole genome sequencing suggested all isolates belong to the same M. porcinum strain and confirmed the source of acquisition to the ice machine. Review of patients' clinical course, including three patients who underwent lung transplantation, suggested a pseudo-outbreak with minimal clinical impact. CONCLUSIONS: NTM, including M. porcinum, are ubiquitous in potable water and institutional water reservoirs. Our findings suggest M. porcinum is a transient colonizer rather than a pathogen. Challenges exist in discerning the role of NTM as a contributor of pulmonary morbidity in patients with CF, and adherence to established guidelines regarding NTM related pulmonary disease remains important.