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

<b>Background:</b> 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. <b>Objectives:</b> ­ We aimed to outline the epidemiology of respiratory NTM isolates in Belgium and to assess their clinical relevance since Belgian data are scarce. <b>Methods:</b> 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). <b>Results:</b> Of the 384 unique patients 60% were male, 56% had a smoking history and 61% had pre-existing lung disease. <i>Mycobacterium avium</i> complex (MAC), <i>M. gordonae</i> and <i>M. xenopi</i> 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 <i>M. abscessus</i> (11/12), <i>M. malmoense</i> (6/7) and <i>M. intracellulare</i> (41/64). <b>Conclusion:</b> In our study MAC was the most commonly isolated NTM species but <i>M. abscessus</i> 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.