Comparative assessment of cartridge based nucleic acid amplification technique (CBNAAT) with gold standard LJ culture and smear microscopy in diagnosis of pulmonary and extra pulmonary tuberculosis in Tripura.

BACKGROUND: The hope of tuberculosis elimination by 2025 has been put in a global dilemma by the emergence of Multidrug Resistant Tuberculosis (MDR-TB). Furthermore, the disparity between smear examination and CBNAAT in low resource settings can hamper the elimination drive in developing nations where infrastructure for culture methods is limited. In this study we compared the results of CBNAAT and smear examination with that of solid culture as the gold standard.

METHODS: A total of 184 pulmonary and extra-pulmonary clinical samples were included in this study. These were then subjected to Ziehl Neelson staining, CBNAAT and solid culture in LJ media. Sensitivity, specificity, Positive Predictive Values and Negative Predictive Values were calculated for bacilloscopy and CBNAAT in comparison to gold standard culture.

RESULT: The overall sensitivity was higher for CBNAAT (97.29 %) but smear microscopy showed higher specificity (92.5 %). PPV and NPV of smear microscopy was 75 % and 97.14 % and for CBNAAT was 55.42 %, and 99.10 % respectively. Sensitivity of culture and smear microscopy done conjointly showed a high sensitivity of 96.97 %. CBNAAT also detected 9 culture and smear negative samples as positive.

CONCLUSION: Diagnostic efficacy of CBNAAT or the Cepheid GeneXpert assay as a screening method for tuberculosis was significantly higher than smear microscopy. However, used conjointly, the scope of differentiating MTB, NTM and RIF resistant TB is expanded. Nevertheless, the need for an accurate on-site technology for the simultaneous identification of NTM and MTB is indubitable at this stage.