DIAGNOSTIC UTILITY OF GENEXPERT MTB/RIF ASSAY IN THE DETECTION OF MYCOBACTERIUM TUBERCULOSIS FROM CLINICALLY SUSPECTED CASES OF TB MENINGITIS IN A TERTIARY CARE HOSPITAL

Tuberculous meningitis (TBM) is one of the most severe forms of Tuberculosis. The aim of the study was to evaluate sensitivity of GeneXpert MTB/RIF (CBNAAT) test in clinically suspected cases of TBM in comparison with MGIT culture, the gold standard test. This study was carried out in the TB Culture & DST Laboratory, Department of Microbiology of a tertiary care Hospital. A total of 741 CSF samples from clinically suspected cases of TBM were simultaneously subjected to CBNAAT and liquid culture using MGIT 960 system in which 46 (6.21%) tested positive and 695 (93.79%) tested negative on CBNAAT while in MGIT culture, 44 (5.94%) samples showed positive growth, 696 (93.93%) were negative and 1 (0.13%) was contaminant. Out of the 46 samples positive on CBNAAT, 7(15.22%) were RIF resistant, 37(80.44%) RIF sensitive and 2 (4.34%) were RIF indeterminate. Out of the total 741 samples tested on CBNAAT and MGIT culture, 24(3.24%) and 674 (90.96%) tested positive and negative by both tests respectively. However, in 22 (2.97%) samples, CBNAAT was positive while MGIT culture was negative and 20 (2.70%) samples showed vice versa results. Xpert MTB/RIF showed sensitivity of 54.54% and specicity of 97.11%. The positive and negative predictive value for Xpert MTB/RIF was 54.54%, and 97.11% respectively. Diagnostic accuracy of Xpert MTB/RIF in comparison to MGIT culture was 94.07%. Although, Gen IV Xpert MTB/RIF is a rapid method for diagnosing MTB, its limit of detection is 131 CFU/mL vis-a-vis Xpert MTB/RIF Ultra is 16 CFU/mL. As, TBM is a paucibacillary infection, the use of Xpert MTB/RIF Ultra in place of Gen IV Xpert MTB/RIF assay could substantially increase the chances of diagnosing TBM in an effective manner.