Comparing diagnostic accuracy of CB-NAAT and ZN staining in diagnosis of Pulmonary and Extra-pulmonary Tuberculosis cases at tertiary care teaching hospital of north India.

Abstract

Background: Continuing the fight to eradicate tuberculosis from India, which has 24 per cent of the world’s total number of TB cases, is a big challenge for the country to achieve its goal of being TB free by 2025. Keeping in view limitation of culture and smear microscopy, a rapid, accurate, point-of-care diagnostic test that is affordable and can be readily implemented is urgently needed. In recent years, cartridge based nucleic acid amplification test (CBNAAT) has been recommended by World Health Organization as a rapid diagnostic test for detection of tuberculosis and rifampicin resistance. In our study we have tried to analyse whether this has proved as a first critical step in controlling tuberculosis. Aim : In this study, we retrospectively compared results for diagnosis of suspected pulmonary and Extrapulmonary tuberculosis cases, from September 2017 to January 2018 for Ziehl-Neelsen (ZN) and GeneXpert (Xpert® MTB/Rif assay) taking culture as gold standard, in the Department of Microbiology DRPGMC&H Kangra at Tanda. Methods: Performance of Xpert was compared to acid-fast microscopic examination using Ziehl-Neelsen (ZN) stain in patients with culture-confirmed tuberculosis. Results:: Out of total 914 specimens of clinically suspected patients of tuberculosis of all age groups ,683(75%) were pulmonary specimens and231(25%)were extrapulmonary .For pulmonary samples, the sensitivity and specificity for CBNAAT samples were 82.3% and 98.5% while that for sputum smear were 63.7% and 99.3%% respectively. For extrapulmonary samples, the sensitivity and specificity for CBNAAT samples were 85.7% and 93.5% respectively; while that for sputum smear were 60.7% and 100% respectively. Conclusion: Although the development of the Xpert MTB/RIF assay is undoubtedly a landmark event in a high TB burden country like India as this test will help in rapid diagnosis of smear-negative and rifampicin resistant TB cases, which were earlier a challenge for the TB control programmes Key Words: Tuberculosis (TB) Cartridge based nucleic acid amplification test (CBNAAT) Rifampicin (RIF),Mycobacterium tuberculosis(MTB),Ziehl Neelsen(ZN)