Performance Assessment of Xpert MTB/RIF Assay for Detecting Pulmonary Tuberculosis and Rifampin Resistance in a Tertiary Care Hospital in Korea

Abstract

This study aimed at evaluating performance of Xpert MTB/RIF (Xpert) regarding detection of pulmonary tuberculosis compared to acid-fast bacilli (AFB) smear and culture, and concordance of rifampin resistance with drug susceptibility test. Specimens simultaneously referred for AFB smear, culture, and Xpert during April 2015 to March 2018 were retrospectively reviewed. Sensitivity, specificity, and mean cycle-threshold (Ct) values of Xpert and rifampin resistance results were analyzed. Results of Xpert for pulmonary tuberculosis were evaluated by AFB smear grade. Among the total of 3,840 specimens, 491 were positive in Xpert and 626 were positive in culture. Sensitivity and specificity of Xpert was 75.6% and 99.4%, respectively. Sensitivity of Xpert in smear-positive/culture-positive specimens was 98.6% and those of smear-negative and trace/culture-positive was 63.1%. Positivity of Xpert in culture-positive specimens were 89.9%/98.6%/95.7%/100.0%/100.0% in smear grade trace/1+/2+/3+/4+. Ct values of 491 specimens significantly lowered as AFB smear grade increased (p<0.0001). Ct of smear-positive/smear-trace/smear-negative specimens were 21.7 ± 4.2/26.5 ± 3.9/27.4 ± 3.6, respectively. Rifampin resistance tested by Xpert and culture was 98.3% concordant. Region covered by probe E was the most frequently mutated (50.0%). Xpert showed reliable performance in detecting pulmonary tuberculosis in smear-positive/culturepositive specimens and further improvements are needed for smear negative/culture positive specimens.

Detection and factors associated with tuberculosis and rifampicin resistance among presumptive patients at the Thailand-Myanmar border

“…Basically, Xpert MTB/RIF can identify RR based on probes for the detection of mutations covering the 81-bp rifampicin resistance-determining region (RRDR), the core region of the rpoB gene. Five probes, A, B, C, D, and E were used in the Xpert MTB/RIF assay to detect RR and the missing detection of the probe identified the specific locus of mutations in the RRDR (Chang et al, 2021). In this study, most of the rifampicin resistance mutations were detected by the drop out of probe E which covers the rpoB nucleotide sequences encoding codons 523-527, followed by the mutations detected by probe D missing.…”