Mycobacterium tuberculosis Dominance over Nontuberculous Mycobacteria Irrespective of Immune Status: An Indian Scenario

In HIV-associated tuberculosis cases, identifying nontuberculous Mycobacteria (NTM) from clinical samples has become essential regarding patients’ treatment and prognosis. This study aims to determine the prevalence of different Mycobacteria species from immunocompromised and immunocompetent patients with suspected tuberculosis attending a tertiary care hospital in Kolkata, India.

Clinical samples from 112 suspected tuberculosis patients were examined by direct microscopy after Ziehl–Neelsen staining. After culture in BacT/ALERT 3D mycobacterial culture system, identification of the causative agents was performed using the GenoType MTCM system.

Culture positivity was higher in immunocompromised patients than in immunocompetent in both pulmonary and extrapulmonary samples. In smear-negative samples, culture positivity in immunocompromised patients (50%) was much higher than in immunocompetent patients (26.67%). Of 78 samples, four were NTMs (5.13%), including 1 M. avium, 1 M. abscessus, and 2 M. fortuitum, and 74 were Mycobacterium tuberculosis (MTBC). Two NTMs belonged to immunocompromised patients and two to immunocompetent individuals. The chance of Mycobacterial infection was higher in patients with a lower CD4 count. Both NTMs found in the immunocompromised group were from patients with a CD4 count<100.

The present study showed that the MTBC is still the primary causative agent in pulmonary and extrapulmonary tuberculosis in this part of India.