Nontuberculous mycobacteria in respiratory samples: species distribution and repeat detection in real-world practice

The frequency of detecting nontuberculous mycobacteria (NTM) in respiratory samples has increased in recent years, which is associated both with improvements in laboratory diagnostics and with the growing prevalence of mycobacterial diseases. At the same time, there is no standardized approach in clinical practice to the interpretation of the initial NTM isolation and indications for repeat microbiological testing, which complicates diagnosis and patient management.

The aim of the study was to assess the detection rate and analyze the species composition of non­tuberculous mycobacteria (NTM) in respiratory samples from patients with suspected tuberculosis referred to a Regional State Autonomous Healthcare Institution “Tomsk Phthisiopulmonology Medical Center”.

Methods. A retrospective study of microbiological assays of 254 patients referred to the Regional State Autonomous Healthcare Institution “Tomsk Phthisiopulmonology Medical Center” in 2023 – 2025 for exclusion of pulmonary tuberculosis was conducted. Patients with at least one positive NTM result from respiratory samples were included. Species identification was performed using Matrix­Assisted Laser Desorption/Ionization Time­of­Flight Mass Spectrometry (MALDI­TOF MS). Depending on the frequency of detection, patients were stratified into three groups: single detection without follow­up, unconfirmed detection upon repeat testing, and confirmed repeated detection. Statistical analysis was performed using the chi­square (χ2) test and Fisher’s exact test with Bonferroni correction.

Results. In the majority of patients (78.4%), NTM were detected once or the detection was not confirmed. Repeated detection was confirmed in 21.7% of cases. Slowly growing NTM predominated (69.3%), with the Mycobacterium avium complex (MAC) being the most common (53.1%). The proportion of MAC increased with repeated detection. These findings support the need to standardize repeat microbiological testing after initial NTM detection to improve diagnostic accuracy and optimize patient management.

Conclusion. The data obtained justify the need for standardization of repeated microbiological control after the first positive result in order to increase diagnostic accuracy and optimize patient routing.

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