Clinical relevance of pulmonary non-tuberculous mycobacterial isolates in three reference centres in Belgium: a multicentre retrospective analysis

Background: Assessing the clinical relevance of non-tuberculous mycobacteria (NTM) isolated from respiratory samples can be challenging. The epidemiology of NTM species and their pathogenicity vary geographically, which can be important to guide clinical decision making. Objectives: ­ We aimed to outline the epidemiology of respiratory NTM isolates in Belgium and to assess their clinical relevance since Belgian data are scarce. Methods: We performed a retrospective multicentre study of all patients identified from the laboratory database with ≥1 respiratory sample growing NTM from January 2010 through December 2017. We collected clinical, radiological and microbiological data by medical record review and assessed clinical significance according to ATS/IDSA criteria for NTM pulmonary disease (NTM-PD). Results: Of the 384 unique patients 60% were male, 56% had a smoking history and 61% had pre-existing lung disease. Mycobacterium avium complex (MAC), M. gordonae and M. xenopi were the most frequently isolated species: 53%, 15% and 8% respectively. 43% of patients met ATS/IDSA criteria of which 28% presented with fibrocavitary disease. NTM-PD was statistically correlated with weight loss (OR 3,59), fibrocavitary lesions (OR 4,45) and positive acid-fast staining (OR 9,28). The most pathogenic species were M. abscessus (11/12), M. malmoense (6/7) and M. intracellulare (41/64). Conclusion: In our study MAC was the most commonly isolated NTM species but M. abscessus was the most pathogenic. Clinicians should consider this local knowledge in treatment decision making. Prospective national data collection could further inform us on this topic.