The impact of non-TB mycobacterial co-isolation in patients with pulmonary TB

Pulmonary TB is diagnosed by isolating Mycobacterium tuberculosis from sputum. Culture conversion, defined as two consecutive negative sputum cultures, guides treatment duration. Non-TB mycobacteria (NTM) species are common in the environment but only cause pulmonary disease in certain patients, and the significance of co-isolation of NTM during TB treatment is unclear. We aimed to assess if NTM co-isolation impacts sputum conversion, treatment duration, or outcomes.

We conducted a retrospective study of pulmonary TB patients treated at West Park Healthcare Centre between 2010 and 2020. Demographics, microbiologic data, and clinical outcomes were extracted. Patients with NTM co-isolation were compared to those with TB-alone.

Among 771 patients, 284 co-isolated NTM. These patients were older (median 58 vs. 49 years) and more often had diabetes (28.5% vs. 18.7%). They had longer time to sputum culture conversion (56 vs. 45.5 days) and were less likely to achieve sputum culture conversion (73.1% vs. 82.7%). NTM co-isolated patients had more persistent cough and sputum at treatment completion.

NTM co-isolation in TB occurs more commonly in older patients, and those with diabetes. Patients who co-isolate NTM during TB treatment are less likely to culture convert, have a longer time to culture conversion, and have more end-of-treatment symptoms.