Incidence and clinical significance of non-tuberculous mycobacteria isolated from clinical specimens during a 2-y nationwide survey

A 2-y nationwide survey of patients in Denmark with non-tuberculous mycobacteria (NTM) cultures was undertaken. Patients were identified by means of records held at the International Reference Laboratory of Mycobacteriology, Statens Serum Institut, Denmark. The objectives were to identify isolated NTM to species level, to describe the incidence of the various species and to evaluate the clinical significance of pulmonary NTM isolates other than M. avium complex (MAC) and M. gordonae. Identification was performed by means of hybridization or sequencing of 16S rDNA. The clinical significance of pulmonary NTM isolates was evaluated by means of questionnaires concerning patients (was sent to the clinicians!) patients who had NTM isolated for the first time using bacteriologic, radiographic and clinical criteria. A total of 1110 specimens (2.1%) from 525 patients grew NTM. After MAC (n = 198) and M. gordonae (n = 168), most patients had M. abscessus (n = 21), M. malmoense (n = 20) and M. xenopi (n = 17) isolated. Of the pulmonary patients, 50.6% met bacteriologic criteria, 75.3% radiographic criteria and 53.4% clinical criteria for significant infection. Almost half of the pulmonary patients met all the criteria for significant NTM infection that could be evaluated. Clinically significant infection was associated with underlying disease in most patients.