Evaluation of Sensitivity and Specificity of CSF Gene Xpert and to Compare it with CSF Culture in Tuberculous Meningits

BACKGROUND: CSF gene Xpert MTB/RIF is a rapid and specific test in diagnosing tuberculous meningitis Rapidity is in terms of 2 hours. It detects the presence of M.bacilli based on real time PCR Advantages being identifying the resistance in single step, less cross contamination, low biohazards and not requiring much trained staffs. The gold standard test is culture but it takes a time of 1 week. The test is based on a real-time heminested PCR test which detects the presence of M. tuberculosis complex bacilli. By using 5molecular beacons that span the rpoBgene81-bp rifampin resistance-determining region (RRDR), the test simultaneously determines susceptibility to rifampin, which can be used as a surrogate marker for multidrug resistance (MDR). The closed-cartridge system makes it possible for the assay to be used outside the laboratory environment, and studies assessing biosafety have suggested that the use of Xpert MTB/RIF carries a smaller biohazard risk than smear microscopy. The risk of cross-contamination is also reduced with the closed cartridge system. The test has shown a sensitivity above 90% for culture positive tuberculosis, with high specificity in sputum samples. Sensitivity in individuals with HIV coinfection is over 80%.Due to the urgency of diagnosis in suspected TBM cases because of a rapid decrease of survival chances with the increase of severity (mortality for grade 1 patients is approximately 20%; for grade 3 it reaches 55%, a rapid, accurate diagnostic test which also is able to identify rifampin resistance could have a great impact on survival. AIM OF THE STUDY: 1. To prospectively determine the sensitivity and specificity of CSF gene Xpert MTB/RIF in a given set of CSF samples and to compare it with gold standard culture. 2. To measure the diagnostic accuracy of gene Xpert MTB/ RIF in CSF culture positive patients. MATERIALS AND METHODS: STUDY POPULATION: SOURCE OF DATA: The study will be conducted on 50 patients admitted to Government Rajaji Hospital & Madurai Medical College, Madurai. Inclusion criteria: Patients aged 18 years with symptoms and signs suggestive of tuberculous meningitis. Exclusion criteria: Viral meningitis, Cerebral malaria, Brain abscess, Malignancy. CONCLUSION: This is a prospective study in our tertiary centre so far, to measure the sensitivity and specificity of gene Xpert MTB/RIFin CSF samples in patients with tuberculous menigitis. “The sensitivity of CSF gene Xpert MTB/RIF in our study was 84.21 and specificity was 66.67%. The positive predictive value was 88.89% and negative predictive value was 57.14%, with these data analysis the gene Xpert MTB/RIFhad a diagnostic accuracy of 80.00% in diagnosing tuberculous menigitis.” In order to reach a quick diagnosis in tuberculous menigitis, using CSF specimens, CBNAAT need to be preferentially used as major tool for the diagnosis and treatment in TBM for reducing the mortality and morbidity of tuberclulous menigitis. Hence CBNAAT had to be authenticated in every centres like our tertiary centre where there is high prevalence of tuberculosis as the test that gives rapid result and also detects rifampicin resistance in a single step which is the major concern for every physician with respect to TBM. Clear guidance should be given by WHO regarding CBNAAT use in CSF samples in suspected TBM patients so that gene Xpert MTB/RIF would play a pivotal role in diagnosis and treatment of one of the most common medical emergency in India.