Nontuberculous Mycobacteria under Scrutiny in the Geneva Area (2015-2020)

Nontuberculous mycobacteria (NTM) are increasingly identified in industrialized countries, and their role as pathogens is more frequently recognized. The relative prevalence of NTM strains shows an important geographical variability. Thus, establishing the local relative prevalence of NTM strains is relevant and useful for clinicians.

Retrospective analysis (2015-2020) of a comprehensive database was conducted including all results of cultures for mycobacteria in a University Hospital (Geneva, Switzerland), covering a population of approximately 500,000 inhabitants. All NTM culture-positive patients were included in the analyses. Patients' characteristics, NTM strains, and time to culture positivity were reported.

Among 38,065 samples analyzed during the study period, 411 were culture-positive for NTM, representing 236 strains, and 231 episodes of care which occurred in 222 patients. Patients in whom NTM were identified were predominantly female (55%), with a median age of 62 years, and a low BMI (median: 22.6 kg/m2). The Mycobacterium avium complex (MAC) was the most frequently identified group (37% of strains) followed by Mycobacterium gordonae (25%) and Mycobacterium xenopi (12%) among the slowly growing mycobacteria (SGM), while the Mycobacterium chelonae/abscessus group (11%) were the most frequently identified rapidly growing mycobacteria (RGM). Only 19% of all patients were treated, mostly for pulmonary infections: the MAC was the most frequently treated NTM (n = 19, 43% of cases in patients treated) followed by RGM (n = 15, 34%) and M. xenopi (n = 6, 14%). Among those treated, 23% were immunosuppressed, 12% had pulmonary comorbidities, and 5% systemic comorbidities. Cultures became positive after a median of 41 days (IQR: 23; 68) for SGM and 28 days (14; 35) for RGM.

In Western Switzerland, M. avium and M. gordonae were the most prevalent NTM identified. Positive cultures for NTM led to a specific treatment in 19% of subjects. Patients with a positive culture for NTM were mostly female, with a median age of 62 years, a low BMI, and a low prevalence of immunosuppression or associated severe comorbidities.