Negligible clinical impact of subsequent non-tuberculous mycobacteria isolation during MDR/RR-TB treatment: a 9-year retrospective cohort study from Wenzhou, China.

Background: The frequency of clinical isolation of non-tuberculous mycobacteria (NTM) in patients with multidrug-resistant or rifampin-resistant tuberculosis (MDR/RR-TB) is increasing, but its relevance remains unclear. This study aimed to assess the frequency of NTM isolation and its clinical relevance in respiratory specimens from MDR/RR-TB patients in Wenzhou, China.

Methods: Medical records of MDR/RR-TB patients with NTM isolated from 2014 to 2022 were reviewed retrospectively. To establish the clinical relevance, the diagnostic criteria for nontuberculous mycobacterial pulmonary disease (NTM-PD) published by the American Thoracic Society (ATS) and Infectious Diseases Society of America (IDSA) were applied.

Results: Between 2014 and 2022, a total of 922 patients were enrolled, among whom 45 (4.9%) cases yielded NTM isolates, resulting in the isolation of 68 distinct NTM strains. The most prevalent NTM species was M. abscessus, accounting for 36.8% (25/68) of the isolates, followed by M. intracellulare at 22.1% (15/68) and M. avium at 8.8% (6/68). Notably, only five cases (0.54%) met the microbiologic criteria specified in the ATS/IDSA guidelines. Four of these cases received no specific NTM treatment and achieved a favorable prognosis with anti-TB therapy. Remarkably, a single case out of 922 (0.11%) was identified as having concomitant MDR/RR-TB and NTM-PD.

Conclusions: The clinical relevance of respiratory NTM isolates in patients with MDR/RR-TB is generally low, with the overwhelming majority of these NTM isolates being either colonizers or contaminants. Consequently, in most cases, those with concomitant NTM isolates do not require specific therapy.