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Free Content The Xpert® MTB/RIF assay evaluation in South Korea, a country with an intermediate tuberculosis burden

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SETTING: A central hospital laboratory in South Korea.

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.
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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: 2012-11-01

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  • The International Journal of Tuberculosis and Lung Disease publishes articles on all aspects of lung health, including public health-related issues such as training programmes, cost-benefit analysis, legislation, epidemiology, intervention studies and health systems research. The IJTLD is dedicated to the continuing education of physicians and health personnel and the dissemination of information on tuberculosis and lung health world-wide.

    Certain IJTLD articles are selected for translation into French, Spanish, Chinese or Russian. They are available on the Union website

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