Introduction Non-Tuberculous Mycobacteria (NTM) are often isolated from patient samples, though their clinical relevance can be unclear. Treatment is not always effective and management decisions are usually based on repeat isolates with compatible clinical features. The presence of other micro-organisms, as well as the specific NTM itself, may be important. Here we report NTM and other microbe isolation frequency and their relationship to management decisions.

Methods All NTM samples isolated from liquid culture systems between 09/05/11 and 03/04/13 at our centre were identified using hospital pathology databases. Subject’s negative mycobacterial cultures plus all positive relevant bacteria and virological isolates, as well as clinical history and progress were reviewed.

Results NTM were isolated on 257 occasions from 102 patients, who provided a total of 693 samples for mycobacterial culture. Adjusting for positive samples obtained within a month of each other, there were 170 isolates - 150 of which came from 90 patients’ pulmonary samples. Common associated clinical conditions were non cystic fibrosis bronchiectasis (28, 31.1%), COPD (11, 12.2%), and HIV infection (6, 6.7%). The most frequent lung isolate was Mycobacterium avium intracellulare Complex, MAC, (47.8%), followed by M. fortuitum(14.4%), M. gordonae (10%), and M. kansasii (8.9%). Seven (7.8%) patients had multiple NTM species identified. 40 (44.4%) of the pulmonary patients also had bacteria or fungi isolated from lung samples. Pseudomonas sp. were present in 12 (13.3%), Haemophilus influenzae in 10 (11.1%), and Staphylococcus aureus in 6 (6.7%) patients. To date, 68.9% have not received regular anti-microbial therapy. 19 (21.1%) are on long term anti-bacterials, and 7 (7.8%) are being treated with specific anti-NTM therapy (5 of these MAC). Over the two year period 483 pulmonary samples have been tested for mycobacteria; at a mean frequency of 5.4 samples per patient, with approximately one in three being NTM positive.

Conclusion Different microbes are frequently isolated on serial lung sampling from patients with NTM. Clinicians often utilise a treatment strategy that focuses on organisms other than NTM to control symptoms. The value of this approach requires longer term assessment, but highlights the importance of systematic, microbial surveillance cultures in pulmonary NTM management.