The Xpert® MTB/RIF assay evaluation in South Korea, a country with an intermediate tuberculosis burden
OBJECTIVE: To evaluate the usefulness of the Xpert® MTB/RIF assay in a country with an intermediate tuberculosis burden.
DESIGN: A total of 71 real-time polymerase chain reaction-positive sputum sediments were tested within 24 h by the Xpert MTB/RIF assay. Mycobacterium tuberculosis detection was compared with smear microscopy and culture. Rifampicin (RMP) resistance was compared with a culture-based method and rpoB gene sequencing. We also assessed the limit of detection for mutant proportions and time savings in diagnosis.
RESULTS: The Xpert MTB/RIF assay detected M. tuberculosis in 71 (100%) specimens (32 smear-positive, 39 smear-negative). This assay showed 100% (62/62) concordance with drug resistance confirmed by culture and 98.4% (61/62) concordance with sequencing. A specimen containing approximately 50% of mutant p.His526Tyr was falsely interpreted as wild-type bacilli by this assay. The minimal detection ratio was 5:1 of mutant vs. wild-type cells. The median time saved was 18.5 days (range 9–30) for the diagnosis of M. tuberculosis and 81.5 days (65–136) for RMP susceptibility in smear-negative, culture-positive patients.
CONCLUSIONS: The Xpert MTB/RIF assay showed high sensitivity in detecting M. tuberculosis with information on RMP resistance, and had a more rapid time to diagnosis compared to conventional tests; however, the location and amount of mutation may affect test sensitivity.
Keywords: M. tuberculosis; automated real-time PCR; rifampicin resistance
Document Type: Research Article
Affiliations: 1: Department of Laboratory Medicine, Seoul National University Hospital, Seoul, South Korea; Department of Laboratory Medicine, National Medical Center, Seoul, South Korea 2: Department of Laboratory Medicine, Seoul National University Hospital, Seoul, South Korea 3: Department of Laboratory Medicine, Seoul National University Boramae Hospital, Seoul, South Korea 4: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Lung Institute of Medical Research Center, Seoul National University College of Medicine, Seoul, South Korea
Publication date: 01 November 2012
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