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

Abstract

Background/objectives: Assessing the clinical relevance of non-tuberculous mycobacteria (NTM) isolated from respiratory samples can be challenging. The epidemiology and pathogenicity of NTM species vary geographically. We aimed to outline the clinical relevance and associated radiological patterns of NTM species isolated in Belgium.

Methods: We performed a retrospective multicentre analysis 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 through medical record review and assessed clinical relevance 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 whom 28% presented with fibrocavitary disease. Weight loss, fever, nodular bronchiectatic and fibrocavitary lesions on chest CT, and a positive acid-fast bacilli (AFB) stain were significantly associated with NTM-PD. The species with the highest pathogenic potential 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 and M. malmoense showed the highest probability of being clinically relevant. Clinical relevance varied not only by species but also by radiological findings on chest CT and AFB staining. Clinicians should consider these elements in their treatment decision making. Prospective data including clinical outcome are needed to provide more robust evidence.

Keywords: Epidemiology; Non-tuberculous mycobacteria (NTM); Non-tuberculous mycobacterial pulmonary disease (NTM-PD); Radiology.

Fig. 1

Selection of our study cohort

Fig. 2

New isolates and diagnoses per year. Histogram with annual detection of new patients with an NTM-yielding respiratory sample (blue) and the annual incidence of new cases of NTM-PD (orange)

Fig. 3

Frequencies of individual species in NTM isolates and diagnoses of NTM-PD. The upper pie chart shows all patients. The lower pie chart shows only patients meeting ATS/IDSA criteria for NTM-PD. *“Other NTM” encompasses all other, rarer isolates < 1% of total. Upper pie chart: M. cellatum; M. florentinum; M. gilvum; M. holsaticum; M. lentiflavum; M. wolinsky/jacuzzi; M. noviomagense; M. novocastrense; M. peregrinum; M. terrae complex. Lower pie chart: M. cellatum; M. florentinum; M. noviomagense; M. peregrinum. **NOS: MAC not further identified and reported as ‘MAC’

Fig. 4

Ratio of clinical significance. Clinical significance per species; presented as a percentage based on the number of cases meeting ATS/IDSA criteria for NTM-PD and the total number of isolates per species. MAC and M. chelonae/abscessus complex, not further specified, were regarded separately. On the left, species of low virulence are found and on the right the most pathogenic species. Figure concept van Ingen et al., Thorax 2009, with permission

Fig. 5

Ratio of clinical significance sorted by radiological presentation. Clinical significance per species; presented as a percentage based on the number of cases meeting ATS/IDSA criteria for NTM-PD and the total number of isolates per species. MAC and M. chelonae/abscessus complex, not further specified, were regarded separately. On the left, species of low virulence are found and on the right the most pathogenic species. In the upper bar cases with fibrocavitary changes are depicted, in the middle bar cases with nodular bronchiectatic changes are presented and in the lower bar cases with neither fibrocavitary nor nodular bronchiectatic changes are shown. Figure concept van Ingen et al., Thorax 2009, with permission