Abstract
Introduction: Tuberculosis (TB) caused by the bacterium Mycobacterium tuberculosis, remains one of the major health problems in India. The recent introduction of Cartridge-Based Nucleic Acid Amplification Test (CBNAAT) also known as Gene Xpert MTB/ RIF assay has significantly transformed the diagnostics of TB. The present study aimed diagnostic usefulness of CBNAAT for diagnosing pediatric tuberculosis in our hospital setting.
 Material and Methods: This study was carried out at department of Pediatric, Skmch Bihar India from oct 2018 to Nov 2019. Total 447 patients showing symptoms and signs of suspected localized and/or disseminated tuberculosis or having history of close contact with diagnosed tuberculosis patients admitted in our hospital during the study period were included in this study. Samples (pulmonary and extrapulmonary) were collected from the subjects and put to test for CBNAAT, Zeihl-Neelsen (ZN) smear and culture.
 Results: Among the pulmonary samples, CBNAAT detected MTB in 23 of the 108 sputum/induced sputum samples (21.29%), 89 of the 248 gastric lavage/aspirate samples (35.88%) and 0 of the 5 bronchoalveolar lavage samples (0%). Among the extrapulmonary samples, CBNAAT detected MTB in 9 of the 63 CSF samples (14.28%), 1 of the 13 pleural fluid samples (7.69%), 0 of the 6 ascitic fluid samples (0%) and 3 of the 4 lymph node aspirate samples obtained by FNAC(75%). Sensitivity, specificity, positive predictive value and negative predictive value of CBNAAT in reference to culture are 90.15%, 98.09%, 95.2%and 95.2%respectively. Sensitivity, specificity, positive predictive value and negative predictive value of CBNAAT in reference to ZN smear are 100%, 91.47%, 76% and 100% respectively.
 Conclusion: CBNAAT assay is a rapid test which identifies both the presence of Mycobacterium tuberculosis (MTB) (with high sensitivity, specificity, positive predictive value and negative predictive value) and rifampicin resistance associated with mutation of rpoB gene in a single test. It also helps to avoid injudicious use of anti-tuberculosis drugs.
 Keywords: CBNAAT; MTB; ZN smear; Culture
Highlights
Pulmonary Tuberculosis (PTB) continues to be an important cause of preventable mortality in both developing and developed nations
Smear microscopy is the cornerstone for the diagnosis of TB in resource-limited settings; it has only modest (3580%) sensitivity and a poor Positive Predictive Value (PPV).[3]
CBNAAT is a highly specific test as it uses 3 specific primers and 5 unique molecular probes to target the rpoB gene of Mycobacterium tuberculosis, which is the critical gene associated with RIF resistance.[9]
Summary
Pulmonary Tuberculosis (PTB) continues to be an important cause of preventable mortality in both developing and developed nations. TB may show symptoms and atypical radiologic findings, indistinguishable from those of community-acquired pneumonia.[5] Quick and accurate detection of the pathogen with its drug susceptibility patterns is vital for treatment initiation and disease control.[6] Rapid molecular tests are recent diagnostic tools that can be used to simultaneously test for PTB and RIF resistance with higher sensitivity than sputum smear microscopy and which could replace conventional culturebased drug susceptibility testing.[7] The CBNAAT detects the presence of TB bacilli and tests for resistance to RIF. CBNAAT, as it is a very cost-effective and rapid test is likely to revolutionize the diagnosis and treatment of PTB.[8] CBNAAT is a highly specific test as it uses 3 specific primers and 5 unique molecular probes to target the rpoB gene of Mycobacterium tuberculosis, which is the critical gene associated with RIF resistance.[9]
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