cThe Xpert MTB/RIF assay (Cepheid, Sunnyvale, CA) is a fully automated, cartridge-based real-time PCR assay designed to detect Mycobacterium tuberculosis and rifampin resistance within 2 h. The performance of the Xpert assay has been evaluated in various clinical settings. However, there are few data comparing the Xpert assay to the Cobas TaqMan MTB test (Roche Diagnostics, Basel, Switzerland), one of the most widely utilized molecular assays for M. tuberculosis detection. In this prospective study, 320 consecutive respiratory specimens were processed simultaneously using acid-fast bacillus (AFB) staining, mycobacterial cultures with both solid and liquid media, and the Cobas and Xpert assays. The Xpert assay was performed with direct respiratory specimens, while the Cobas assay was done with decontaminated concentrated specimens. Based on the culture as a reference method, the overall sensitivities of the Cobas and Xpert assays were 71.4% and 67.9%, respectively. When AFB smear results were taken into consideration, the sensitivities of the Cobas assay for smear-positive and -negative specimens were 87% and 54%, while those of the Xpert assay were 67% and 69%, respectively. The Cobas assay showed 100% specificity and 100% positive predictive value (PPV) regardless of smear results, while the Xpert assay showed 100% specificity and 100% PPV for smear-positive specimens but 98% specificity and 60% PPV for smear-negative specimens. In conclusion, the Xpert assay showed performance that was slightly inferior to that of the Cobas assay but seems useful for the rapid detection of M. tuberculosis, considering that it was performed without laborious and time-consuming decontamination and concentration procedures.

Bacillus Calmette-Guërin (BCG) has been traditionally used as a vaccine against tuberculosis. Further, intravesical administration of BCG has been shown to be effective in treating bladder cancer. Although BCG contains a live attenuated strain of Mycobacterium bovis, complications such as M. bovis BCG infection caused by BCG administration are extremely rare. Here, we report a case of BCG infection occurring after intravesical BCG therapy. A 67-yr-old man presented with azotemia and weight loss. He had been diagnosed with bladder cancer 4 yr back, and had undergone transurethral resection of the bladder tumor and intravesical BCG (Tice strain) therapy at that time. An acid-fast bacterial strain was isolated from his urine sample. We did not detect Mycobacterium tuberculosis protein 64 (MPT-64) antigen in the isolates obtained from his sample, and multiplex PCR and PCR-reverse blot hybridization assay indicated that the isolate was a member of the M. tuberculosis complex, but was not M. tuberculosis. Finally, sequence analysis of 16S ribosomal RNA and DNA gyrase, subunit B (gyrB) suggested that the organism was M. bovis or M. bovis BCG. Although we could not confirm that M. bovis BCG was the causative agent, the results of the 3 molecular methods and the MPT-64 antigen assay suggest this finding. This is an important finding, especially because M. bovis BCG cannot be identified using common commercial molecular genetics tools.

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