Evaluation of Xpert MTB/Rif Versus Mycobacterium Growth Indicator Tube 960 for Rifampicin Resistance Detection in Extrapulmonary Isolates.

BACKGROUND

Extrapulmonary tuberculosis (EPTB) accounts for 15%-20% of all tuberculosis (TB). The diagnosis of EPTB is challenging and the emergence of drug-resistant EPTB further threatens the progress toward end TB strategy. Early detection of EPTB is crucial for initiation of appropriate treatment. This study aimed to detect rifampicin resistance (RR) in Mycobacterium tuberculosis Complex (MTBC) from EPTB samples using Xpert Mycobacterium tuberculosis (MTB)/Rif, Mycobacterium Growth Indicator Tube 960 (MGIT960), and Lowenstein Jensen (LJ) medium and compare RR detected by Xpert MTB/Rif and MGIT960 against LJ proportion method.

METHODS

Laboratory-based cross-sectional study was conducted at a tertiary care hospital, New Delhi, from October 2019 to September 2021. A total of 822 EPTB samples were subjected to MGIT960 culture and Xpert MTB/Rif simultaneously. First 30 samples that were MGIT960 flagged and confirmed as MTBC using MPT-64 detection kit were included for rifampicin susceptibility testing by MGIT960 system and LJ proportion method. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of each method were calculated with LJ proportion as the gold standard.

RESULTS

With 30 samples analyzed for RR detection, the overall sensitivity, specificity, PPV, NPV, and accuracy of Xpert MTB/Rif were 50%, 100%, 100%, 96.5%, and 96.6%, respectively, and of MGIT were 100%, 100%, 100%, 100%, and 100%, respectively, with gold standard.

CONCLUSION

While Xpert MTB/Rif provides rapid results and serves as useful initial diagnostic tool, it should be integrated with phenotypic methods such as MGIT960, especially in Xpert MTB/Rif negative cases to confirm clinically suspected EPTB.