Comparison of the Xpert MTB/RIF and Cobas TaqMan MTB Assays for Detection of Mycobacterium tuberculosis in Respiratory Specimens

Abstract

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.

Comparison of the Genedia MTB Detection Kit and the Cobas TaqMan MTB Assay for Detection of Mycobacterium tuberculosis in Respiratory Specimens

“…According to previous studies, the sensitivity and specificity ranges of the Cobas assay are 71.4% to 97.2% and 95.8% to 100%, respectively (6)(7)(8)(9)(10)(11)(12)(13). The sensitivity (78.8%) and specificity (99.5%) of the Cobas assay in this study were also quite similar to those seen in our previous studies (6,7).…”

“…The sensitivity (78.8%) and specificity (99.5%) of the Cobas assay in this study were also quite similar to those seen in our previous studies (6,7). The performance of the Genedia assay was comparable to that of the Cobas assay, with a kappa value of 0.95.…”

Evaluation of the Abbott RealTi m e MTB and RealTi m e MTB INH/RIF Assays for Direct Detection of Mycobacterium tuberculosis Complex and Resistance Markers in Respiratory and Extrapulmonary Specimens

“…Consequently, nucleic acid amplification tests (NAATs), such as PCR assays that allow for the fast and accurate detection of Mycobacterium tuberculosis complex (MTBC) DNA directly in clinical specimens, have become an indispensable tool in TB diagnostics over the last several decades. Most commercial tests show excellent specificity and sensitivity rates with smear-positive specimens while sensitivity rates range from 49% to 78% with smearnegative samples (2)(3)(4)(5)(6)(7).…”

Evaluation of the Diagnostic Performance of Xpert MTB/RIF Test for the Detection of Mycobacterium tuberculosis and Rifampin Resistance in Clinical Samples

“…Aktif TB olgularının ve çoğul ilaç dirençli (ÇİD) suşların hızlı tanısının, TB nedenli morbidite ve mortaliteyi azaltacağı ve etkenin toplumda yayılımının önlenmesine katkıda bulunacağı bildirilmektedir 2,3 . Ancak, TB basilinin kültürde üretilmesi, tanımlanma süreçleri ve ilaç duyarlılığının belirlenmesi zaman alıcı (4-8 hafta) ve güç laboratuvar işlemlerini gerektirmektedir.…”

“…Ancak, TB basilinin kültürde üretilmesi, tanımlanma süreçleri ve ilaç duyarlılığının belirlenmesi zaman alıcı (4-8 hafta) ve güç laboratuvar işlemlerini gerektirmektedir. Geliştirilen otomatize kültür, tanımlama ve duyarlılık sistemleri ile örnekteki canlı basil yüküne göre bu süreler 10-12 güne kadar indirilebilmiş olmasına rağmen, bu süre halen istenilen düzeyde değildir [2][3][4] . XpertMTB/RIF testi (Cepheid, ABD), eş zamanlı olarak M. tuberculosis varlığı ile rifampin (RIF) direncini direkt hasta örneğinden iki saatten kısa bir sürede saptayabilen kolay ve hızlı nükleik asit amplifi kasyon testi olarak son yıllarda kullanıma girmiştir 5 .…”