Identification of Mycobacterium tuberculosis and rifampin resistance in clinical specimens using the Xpert MTB/RIF assay.

Purpose. The Xpert MTB/RIF assay is a novel real-time polymerase chain reaction technique for the detection of the Mycobacterium tuberculosis (MTB) complex and rifampin (RIF) resistance. We evaluated the performance of this assay in identifying MTB and resistance to RIF in clinical specimens. Materials and Methods. We analyzed clinical specimens from 383 patients with suspected TB who were hospitalized at a secondary hospital in Korea. Specimens were processed using the Xpert MTB/RIF assay, acid-fast bacilli smear and culture, and drug susceptibility test (DST). Results. Among the 444 clinical samples analyzed, the Xpert MTB/RIF assay identified MTB in 56 (13.8%) of 405 respiratory specimens, but did not detect MTB in the remaining 39 non-respiratory specimens. Of the 65 pulmonary TB patients, 52 (80.0%) were confirmed by using mycobacterial culture as a reference standard. The sensitivity, specificity, PPV, and NPV of the Xpert MTB/RIF assay were 73.85%, 99.03%, 94.12%, and 94.72%, respectively. Among five patients with RIF resistance determined by the Xpert MTB/RIF assay, four (80%) were confirmed as suffering from multidrug-resistant (MDR) TB by DST. Conclusions. The Xpert MTB/RIF assay appears to be an accurate, simple, and useful technique for detecting MTB, especially in respiratory specimens. However, RIF resistance, if detected, should be verified with DST.