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Updated: Jul 2, 2026

The MODS method for diagnosis of tuberculosis and multidrug resistant tuberculosis
Published on: August 11, 2008
Performance of Molecular Diagnostics in Strengthening Tuberculosis Detection and Drug Resistance Surveillance: A
Nithya S Roy1, Kiran Bala1, Tamanna Bordoloi1
1Department of Microbiology, All India Institute of Medical Sciences, New Delhi, India.
Background:
Tuberculosis (TB) remains a major public health challenge, with India bearing the largest global burden. Rapid molecular diagnostics such as GeneXpert Mycobacterium tuberculosis /rifampicin (MTB/RIF), Truenat MTB/MTB Plus, and first-line line probe assay (FL-LPA) have improved case detection and RIF resistance identification, but their comparative performance with conventional Ziehl-Neelsen (ZN) smear microscopy and mycobacteria growth indicator tube (MGIT) culture requires evaluation.
Methods:
A 16-month retrospective observational study (January 2024-April 2025) at a tertiary care hospital in New Delhi analyzed 9468 clinical specimens. Theis was to compare the diagnostic performance of molecular methods such as GeneXpert MTB/RIF, Truenat MTB/MTB Plus, and FL-LPA with ZN smear microscopy and MGIT culture for pulmonary and extrapulmonary TB, and to assess RIF resistance detection. All samples underwent ZN smear, MGIT culture, and molecular testing. Nucleic acid amplification test (NAAT)- positive samples were subjected to FL-LPA for resistance profiling.
Results:
Out of 9468 clinical specimens analyzed, MTB was detected in 989 (10.45%) cases. Positivity was slightly higher in pulmonary samples (11.4%) compared to extrapulmonary samples (9.5%). RIF resistance was identified in 61 (6.2%) cases, whereas 36 (3.64%) results were indeterminate, most of which occurred in specimens with very low bacillary load. ZN smear microscopy detected only 19.11% of NAAT-positive samples, and smear positivity increased significantly with increasing bacterial load ( P < 0.001). Among the 660 samples evaluated by both NAAT and MGIT culture, concordant positivity was observed in 30 cases, with overall agreement improving as bacillary load increased (overall agreement: 29.7%). FL-LPA detected RIF resistance in 9 of 44 samples tested and revealed discordance with NAAT results in several cases.
Conclusion:
GeneXpert MTB/RIF and Truenat MTB Plus outperform smear microscopy and MGIT in sensitivity, particularly for low-bacillary load. FL-LPA enhances resistance detection, identifying additional RIF-resistant cases missed by NAAT. Incorporating NAAT as the frontline diagnostic, complemented by LPA and culture, can strengthen TB detection and drug resistance surveillance in high-burden settings.
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