Detection of tuberculous meningitis by various microbiological modalities at a tertiary care hospital in north India

Background & Objectives: Tuberculous meningitis is a common infection of the CNS, posing significant diagnostic and management challenges. Death in TBM patients is strongly associated with delay in diagnosis and treatment. Since, any single conventional or automated method for diagnosis of TBM has limited sensitivity; the main objectives of this study was – 1. Detect TBM by a combination of Direct Microscopy by ZN Staining, Culture by solid (LJ) and liquid media (BacT/Alert), besides GeneXpert (RTPCR) in clinically suspected cases.; 2. Evaluate the role of GeneXpert for detection of Mycobacterium tuberculosis in CSF and demonstrate the sensitivity, specificity, PPV and NPV of GeneXpert in comparison with a set composite reference standard. Materials and Methods: This was a prospective cross-sectional study carried out by the Department of Microbiology, GMC, Srinagar, from August ’17 to September ’19 CSF samples of 450 patients suspected of TBM were included in the study. CSF volume was devised which comprised of culture, ZN staining and empirical diagnosis. The samples were tested by ZN staining, solid culture, liquid culture and GeneXpert MTB/RIF using proper protocols. Patient details were obtained on a preformed proforma. Results: Of the 450 suspected patients, 10% had Definitive TBM. The median age was 35 years with an almost equal male to female ratio. The sensitivities of ZN staining, Solid culture, liquid culture and Gene Xpert were 3%, 38%, 76% and 63% respectively. The specificity was 100% for all these tests, 95% CI being, 99-100%. The NPV was 84.02%, 100%, 91% and 93.6% whereas, the PPV was 84.89%, 100%, 100% and 99.1% respectively. Rifampicin resistance was positive in 2%. 95% cases had a very low bacillary load and 2.2% patients showed low and medium bacillary load. 12% patients had concomitant pulmonary TB and 10% with other forms of extrapulmonary TB. Conclusion: Gene/Xpert as a frontline diagnostic tool, is a game changer. It abridges presumpt