• Jeonghyun Chang, Heungsup Sung, Kyung-Wook Jo, Tae Sun Shim, and Mi-Na Kim.
• Department of Laboratory Medicine, University of Ulsan College of Medicine and Asan Medical Center, Korea.
• Jpn. J. Infect. Dis. 2021 Mar 31.

AbstractThis 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/culture-positive specimens and further improvements are needed for smear negative/culture positive specimens.

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