Comparative performance of Line Probe Assay (version 2) and Xpert® MTB/RIF assay for early diagnosis of rifampicin resistant pulmonary tuberculosis.

Background The emergence of drug resistant tuberculosis (TB), is a major menace to cast off TB worldwide. Line probe assay (GenoType MTBDRplus ver. 2) and Xpert® MTB/RIF assays are two rapid molecular TB detection/diagnostic tests. Objective To compare the performance of line probe assay (LPA) and Xpert® MTB/RIF assay for early diagnosis of rifampicin-resistant (RR) TB in acid-fast bacillus (AFB) smear-positive and negative sputum samples. Methods A total 576 presumptive multidrug-resistant TB (MDR-TB) patients were selected and subjected to AFB microscopy, Xpert® MTB/RIF assay and recent version of LPA (GenoType MTBDRplus assay ver.2) tests directly on sputum samples. Results were compared with phenotypic culture and drug susceptibility testing (DST). DNA sequencing was performed with rpoB gene for samples with discordant rifampicin susceptibility results. Results Among culture-positive samples, Xpert® MTB/RIF assay detected Mtb in 97.3% (364/374) of AFB smear-positive samples and 76.5% (13/17) among smear-negative samples, and the corresponding values for LPA test (valid results with TUB band) were 97.9% (366/374) and 58.8% (10/17) respectively. For detection of RR among Mtb positive molecular results, the sensitivity of Xpert® MTB/RIF assay and LPA (after resolving discordant phenotypic DST results with DNA sequencing) were found to be 96% and 99% respectively. Whereas, specificity of both test for detecting RR were found to be 99%. Conclusion We conclude that although Xpert® MTB/RIF assay is comparatively superior to LPA in detecting Mtb among AFB smear-negative pulmonary TB. However, both tests are equally efficient in early diagnosis of AFB smear-positive presumptive RR-TB patients.