Cobas TaqMan MTB Research Articles

Usefulness of Xpert MTB/RIF Ultra to Rapidly Diagnose Sputum Smear-Negative Pulmonary Tuberculosis Using Bronchial Washing Fluid.

This study evaluated the performance of the Xpert MTB/RIF Ultra assay (Xpert Ultra) to detect smear-negative pulmonary tuberculosis (PTB). Xpert Ultra assay was prospectively performed using bronchial washing fluid (BWF) in comparison to COBAS TaqMan MTB (COBAS) assay and mycobacterial culture. Of the 165 enrolled participants, 27 (16.4%) had PTB based on composite reference standard and 16 (9.7%) had culture-confirmed PTB. By the composite reference standard of PTB, the sensitivity of Xpert Ultra (63.0, 95% confidence interval, CI, 42.4–80.6%) was higher than the COBAS assay (25.9%, P = 0.006), BWF-culture (33.3%, P = 0.029) and sputum-culture (37.0%, P = 0.057). Meanwhile, the specificity of Xpert Ultra was 99.3% which was slightly lower than the 100.0% specificity of the COBAS assay (P = 1.000) and cultures (P = 1.000). Against the reference standard of culture-confirmed PTB, Xpert Ultra also had a higher sensitivity (62.5, 95% CI, 35.4–84.8%) than the COBAS assay (31.3%, P = 0.077) and was similar to BWF-culture (56.3%, P = 0.719) and sputum-culture (62.5%, P = 1.000). However, one subject with previously treated old PTB had a false-positive result on the Xpert Ultra assay. This prospective study showed Xpert Ultra assay using BWF had better sensitivity than COBAS assay and mycobacterial cultures but could represent a false positive in patients with inactive old PTB.

Development of a high sensitivity TaqMan-based PCR assay for the specific detection of Mycobacterium tuberculosis complex in both pulmonary and extrapulmonary specimens

Tuberculosis (TB) causes a heavy health burden worldwide, especially in developing countries. The need for the rapid and accurate diagnosis of TB has not been satisfied, especially for extra-pulmonary specimens or specimens with acid fast stain (AFS)-negative condition. Development and validation of a novel, sensitive and specific assay for diagnosing TB is essential. We developed IS4 primer/probe based on insertion sequence 6110 (IS6110). A qPCR assay was designed for detecting a specific region in IS6110 by BLAST. The IS4 primer/probe concentration, qPCR efficiency and various of PCR additives were evaluated and optimized. Thirty-four species of commonly isolated microorganisms were used for evaluating the analytical specificity. Moreover, 130 clinical specimens were collected for evaluating the performance versus Cobas TaqMan MTB (CTM) assay kit and culture. The amplification efficiencies of IS4 were 99.61% and 102.61% without and with internal control DNA (Bacteriophage Lambda), respectively. Dimethyl sulfoxide outperformed glycerol or BSA for eliciting the most effective amplification and the lowest limit of detection. In evaluating the clinical performance, various specimen types were collected. IS4 demonstrated a high degree of agreement (kappa = 0.71) with CTM. The clinical sensitivity and specificity of IS4 and CTM were 92.11% (35/38), 82.61% (76/92), 84.21% (32/38) and 95.65% (88/92), respectively. The clinical sensitivity and specificity of IS4 were similar for both pulmonary [92.00% (23/25) and 76.92% (30/39), respectively] and extrapulmonary [92.31% (12/13) and 86.79% (46/53), respectively] specimens. Among AFS-negative cases, the clinical sensitivity and specificity remained 90.48% (19/21) and 83.91% (73/87), respectively, with culture as the gold standard. We concluded that IS4, a new primer/probe pair for TaqMan based qPCR assay, was developed, optimized, and validated for the sensitive and specific detection of TB among various specimen types. The performance was not compromised under AFS-negative conditions.

Performance evaluation of the Cobas TaqMan MTB assay on respiratory specimens according to clinical application

ObjectiveTo evaluate the performance of the Cobas TaqMan MTB assay (Cobas assay) with respect to its clinical application. MethodsThis was a retrospective analysis of 1154 results from 1034 patients for whom mycobacterial cultures and the Cobas assay were performed simultaneously. Based on the patient medical records, two categories of clinical application were defined: (1) the diagnosis of patients with a high probability of pulmonary tuberculosis according to clinical and radiological features (n=128), and (2) the exclusion of tuberculosis in clinically indeterminate patients (n=1026). Standard culture was used as the reference method. ResultsThe sensitivity of the Cobas assay for the detection of Mycobacterium tuberculosis was 70.4% (95% confidence interval (CI) 49.7–85.5%) for category 1, but only 25.0% (95% CI 4.5–64.4%) for category 2. The specificity was ≥95.0% for both categories. The positive predictive value was 79.2% (95% CI 57.3–92.1%) for category 1 and 33.3% (95% CI 6.0–75.9%) for category 2, while the negative predictive value was 92.3% (95% CI 85.0–96.4%) for category 1 and 99.4% (95% CI 98.7–99.8%) for category 2. ConclusionsThe results of this study indicate that Cobas assay results must be interpreted carefully according to the clinical purpose of the assay.

Early detection of Mycobacterium tuberculosis complex in BACTEC MGIT cultures using nucleic acid amplification.

We evaluated the application of nucleic acid amplification (NAA) in liquid cultures for the early detection of Mycobacterium tuberculosis. The Cobas TaqMan MTB test, IS6110 real-time PCR, and hsp65 PCR-restriction fragment length polymorphism (RFLP) analysis were used to detect BACTEC MGIT 960 (MGIT) cultures on days 3, 5, 7, and 14. The procedure was initially tested with a reference strain, H37Rv (ATCC 27294). Subsequently, 200 clinical specimens, including 150 Acid Fast bacillus (AFB) smear-positive and 50 AFB smear-negative samples, were examined. The Cobas TaqMan MTB test and IS6110-based PCR analysis were able to detect M. tuberculosis after 1day when the inoculum of H37Rv was >3 x 10(-2) CFU/ml. After a 5-day incubation in the MGIT system, all three NAA assays had a positive detection regardless of the inoculum size. After a 1-day incubation of the clinical specimens in the MGIT system, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for the Cobas TaqMan MTB assay were 70.2%, 100%, 100%, and 82.3% respectively. For IS6110-based PCR analysis, these values were 63.1%, 100%, 100%, and 78.9%, and were 88.1%, 100%, 100%, and 92.1% respectively for hsp65 PCR-RFLP analysis. After a 3-day incubation, the specificity and PPV were 100% for all three NAA tests; the Cobas TaqMan MTB assay had the best sensitivity (97.6%) and NPV (98.3%). The sensitivity, specificity, PPV, and NPV for conventional culture analysis were 98.8%, 100%, 100%, and 99.1%. Thus, NAA may be useful for the early detection of M. tuberculosis after 3 days in MGIT.

Sensitivity and specificity of Cobas TaqMan MTB real-time polymerase chain reaction for culture-proven Mycobacterium tuberculosis: meta-analysis of 26999 specimens from 17 Studies.

Since 2010, studies on the diagnostic accuracy of COBAS TaqMan MTB (CTM) have been frequently reported with an unignorable discrepancy. The key inclusion criterion for this systematic review was original studies that could provide sufficient data for calculating the sensitivity and the specificity of CTM for M tuberculosis (TB) or M tuberculosis complex. The reference test was Mycobacterium culture. We used bivariate model for meta-analyses. Of the 201 candidate articles, we finally identified 17 eligible articles.Concerning the respiratory specimens, 1900 culture positive specimens and 20983 culture negative specimens from 15 studies were assessed. This provided the summary estimate sensitivity of 0.808 (95% CI 0.758–0.850) and the summary estimate specificity of 0.990 (95% CI 0.981–0.994). The area under curve was 0.956. The diagnostic odds ratio was 459 (95% CI 261–805, I2 26%). For the smear positive respiratory specimens, the sensitivity was 0.952 (95% CI 0.926–0.969) and the specificity was 0.916 (95% CI 0.797–0.968). For the smear negative respiratory specimens, the sensitivity and the specificity were 0.600 (95% CI 0.459–0.726) and 0.989 (95% CI 0.981–0.993), respectively. The diagnostic accuracy was poorer for the non-respiratory specimens, than for the respiratory specimens, but was acceptable. We believe that the information obtained from this study will aid physicians’ decision making.

Diagnostic value of nine nucleic acid amplification test systems for Mycobacterium tuberculosis complex

Objective: In this study, nine commercial Nucleic Acid Amplification Test Systems (NAATs) were evaluated for diagnostic performance of Mycobacterium tuberculosis complex (MTBC) from smear positive sputum species (SPss) and smear negative sputum specimens (SNss). Methods: Sixty SPss and 55 SNss were examined microscopically by Ehrlich Ziehl Neelsen (EZN) staining method, and also inoculated on Lowenstein Jensen (LJ) medium for culture. The sensitivity and specificity of nine NAATs were calculated according to LJ culture method accepted as gold standard. Results: When LJ culture results were taken as gold standard; the sensitivity rates of method COBAS Amplicor MTB (Method A), GenProbe MTD (Method B), Cobas TaqMan MTB PCR (Method C), iCycler iQ RT PCR (Method D), TaqMan PCR AB 5700 (Method E), TaqMan PCR AB7700 (Method F), LightCycler® 480 RT PCR (Method G), Rotor Gene RT PCR (Method H) and the AdvanSure TB/NTM RT PCR (Method I) for SPss were 98.3 %, 93.3 %, 96.7 %, 100 %, 93.3 %, 100 %, 100 %, 100 % and 100 %, respectively. The sensitivity was 53.84% for the methods A, B, D, E, G and I; 38.46% for the method C and H; 61.5% for the method F for the method I in SNss. There were no statistical significant differences between the nine NAATs (p≥0.05). The specificity was 100% for all nine NAATs in SNss. The positivity rates of methods were 53.8% for methods A, B, D, E, G, I; 38.5% for methods C and H, and 61.5% for method F in SNss. These rates were 100% for D, F, G, H and I; 98.3% for method A; 96.7% for method C; 93,3% for methods B and E in SPss. Statistical analysis showed that there was no statistically significant differences among the nine NAATs (p≥0.05). Conclusion: It is concluded that the nine NAATs might be useful for detecting MTBC from SPss, but not effective for SNss. J Microbiol Infect Dis 2015;5(3): 103-109 Key words: Tuberculosis, polymerase chain reaction, nucleic acid amplification test, smear positive, smear negative, sputum

Evaluation of the Cobas TaqMan MTB test for detection of Mycobacterium tuberculosis complex

Background: The Cobas TaqMan MTB assay is used for rapid detection of the Mycobacterium tuberculosis complex (MTC) in clinical samples. It is only validated for respiratory samples, but is often requested by physicians for non-respiratory specimens. The aim of this study was therefore to evaluate the performance of this assay in clinical praxis in a country with low prevalence of tuberculosis (TB). Methods: The results from 2388 respiratory and 1005 non-respiratory human specimens were analyzed by this real-time PCR technique. Using culture results as the gold standard, the sensitivity, specificity, positive predictive value (PPV), and negative predictive values (NPV) of the PCR results were calculated. Results: For smear-positive respiratory specimens all the four values investigated were 100%. The number of smear-positive non-respiratory specimens was only eight, and all of these eight specimens reacted positively. Sensitivity was 51% for smear-negative respiratory specimens, and 47% for smear-negative non-respiratory specimens. When all non-respiratory specimens were analyzed together the sensitivity was 51%. Specimens from 16 patients were PCR-positive but culture-negative and these cases are discussed. In one case, TB DNA was still present in sputum 2 years after a successful treatment. Conclusion: The study shows that the Cobas TaqMan MTB assay performs well in smear-positive samples, while the sensitivities are unsatisfactory for both respiratory and non-respiratory smear-negative specimens. Furthermore, the analyses emphasize that this assay cannot be used to evaluate treatment or contagiousness, or to detect relapses or screen for TB.

Multicenter evaluation of Seegene Anyplex TB PCR for the detection of Mycobacterium tuberculosis in respiratory specimens.

Culture is the gold standard for diagnosis of tuberculosis, but it takes 6 to 8 weeks to confirm the result. This issue is complemented by the detection method using polymerase chain reaction, which is now widely used in a routine microbiology laboratory. In this study, we evaluated the performance of the Seegene Anyplex TB PCR to assess its diagnostic sensitivity and specificity, and compared its results with the Roche Cobas TaqMan MTB PCR, one of the most widely used assays in the world. Five university hospitals located in the Chungcheong area in South Korea participated in the study. A total of 1,167 respiratory specimens ordered for acid-fast bacilli staining and culture were collected for four months, analyzed via the Seegene Anyplex TB PCR, and its results were compared with the Roche Cobas TaqMan MTB PCR. For detection of Mycobacterium tuberculosis, the diagnostic sensitivity and specificity of the Anyplex TB PCR were 87.5% and 98.2% respectively, whereas those of the Cobas TaqMan were 92.0% and 98.0% respectively (p value > 0.05). For smear-positive specimens, the sensitivity of the Anyplex TB PCR was 95.2%, which was exactly the same as that of the Cobas TaqMan. For smear-negative specimens, the sensitivity of the Anyplex TB PCR was 69.2%, whereas that of the Cobas TaqMan TB PCR was 84.6%. For detection of MTB, the Seegene Anyplex TB PCR showed excellent diagnostic performance, and high sensitivity and specificity, which were comparable to the Roche Cobas TaqMan MTB PCR. In conclusion, the Anyplex TB PCR can be a useful diagnostic tool for the early detection of tuberculosis in clinical laboratories.

Accuracy of polimerase chain reaction for the diagnosis of pleural tuberculosis

Polymerase chain reaction (PCR)-based techniques to detect Mycobacterium tuberculosis DNA in respiratory specimens have been increasingly used to diagnose pulmonary tuberculosis. Their use in non-respiratory specimens to diagnose extrapulmonary tuberculosis is, however, controversial. In this study, we estimated the accuracy of three in-country commercialized PCR-based diagnostic techniques in pleural fluid samples for the diagnosis of pleural tuberculosis. Patients underwent thoracenthesis for diagnosis purposes; pleural fluid aliquots were frozen and subsequently submitted to two real time PCR tests (COBAS(®)TAQMAN(®)MTB and Xpert(®)MTB/Rif) and one conventional PCR test (Detect-TB(®)). Two different reference standards were considered: probable tuberculosis (based on clinical grounds) and confirmed tuberculosis (bacteriologically or histologically). Ninety-three patients were included, of whom 65 with pleural tuberculosis, 35 of them confirmed. Sensitivities were 29% for COBAS(®)TAQMAN(®)MTB, 3% for Xpert(®)MTB/Rif and 3% for Detect-TB(®); specificities were 86%, 100% and 97% respectively, considering confirmed tuberculosis. Considering all cases, sensitivities were 16%, 3% and 2%, and specificities, 86%, 100%, and 97%. Compared to the 95% sensitivity of adenosine deaminase, the most sensitive test for pleural tuberculosis, the sensitivities of the three PCR-based tests were very low. We conclude that at present, there is no major place for such tests in routine clinical use.

Evaluation of the Cobas TaqMan MTB real-time PCR assay for direct detection of Mycobacterium tuberculosis in respiratory specimens

The Cobas TaqMan MTB assay is a real-time PCR (qPCR) kit for rapid detection of Mycobacterium tuberculosis from clinical specimens. There are, however, limited studies validating its performance. We performed a prospective study in two hospitals in Taiwan on 586 respiratory specimens. By using culture as the reference method, the sensitivity and specificity of the Cobas TaqMan MTB assay were found to be 82.7 and 96.5 %, respectively. The sensitivity of the Cobas TaqMan MTB assay in acid-fast stain-negative respiratory specimens was only 34.9 %. Five specimens from five patients were positive for M. tuberculosis by the Cobas TaqMan MTB assay but were negative for M. tuberculosis by conventional culture methods. A diagnosis of pulmonary tuberculosis (TB) was made based on clinical and radiological findings as well as the response to anti-TB treatment in these five patients. Addition of data from these five specimens with discrepant results (PCR vs culture) from patients with symptoms clinically compatible with TB increased the sensitivity of the Cobas TaqMan MTB assay to 83.1 %. The Cobas TaqMan MTB assay is a rapid identification tool with a high degree of specificity for the direct detection of M. tuberculosis in respiratory specimens. The sensitivity for detecting acid-fast smear-negative respiratory specimens, however, is low.

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

The 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.

Performance of Cobas TaqMan MTB for Detection of Mycobacterium tuberculosis Complex in Respiratory Specimens

Objective: Because tuberculosis is a major global health problem, rapid and accurate identification of Mycobacterium tuberculosis complex (MTBC) in clinical specimens is essential for the control of the spread of tuberculosis. One of real-time polymerase chain reaction assays for direct detection of MTBC, Cobas TaqMan MTB (Roche Diagnostics) assay has been widely used in clinical setting in Korea. The aim of study was to evaluate of the performance of Cobas TaqMan MTB assay in respiratory specimens. Methods: Total of 619 respiratory specimens (572 sputum specimens and 47 bronchoalveolar washing fluid specimens) was collected in August and September, 2011. All specimens were analyzed for the detection of MTBC by direct smear examination, mycobacterial culture, and Cobas TaqMan MTB assay. Results: When the culture method was used as the gold standard test for comparison, Cobas TaqMan MTB assay for detection of MTBC had a sensitivity and specificity of 80.9% (38/47) and 100% (572/572), respectively. Positive predictive value and negative predictive value of Cobas TaqMan MTB assay was 100% and 98.5%, respectively. The sensitivity of Cobas TaqMan MTB assay was 100% in AFB smear-positive samples and 59.1% in smear-negative samples. Conclusion: Cobas TaqMan MTB assay has an excellent performance in smear-positive respiratory specimens. But performance of Cobas TaqMan MTB assay in smear-negative respiratory samples was not good. For detection of paucibacillary tuberculosis, conventional mycobacterial culture must not be replaced by Cobas TaqMan MTB assay.

Comparison of PNA probe-based real-time PCR and Cobas TaqMan MTB for detection of MTBC

We compared the sensitivities and specificities of peptide nucleic acid (PNA) probe-based real-time PCR (PNAqPCR™ TB/NTM) and Cobas TaqMan MTB assays for detection of Mycobacterium tuberculosis complex (MTBC) in clinical specimens. A total of 425 clinical specimens including 360 respiratory specimens and 65 non-respiratory specimens were evaluated for comparative analysis. In respiratory specimens, the sensitivity of TaqMan MTB and PNAqPCR assay for detection of MTBC was 82.9% and 91.5%, respectively. In non-respiratory specimens, the sensitivity of the TaqMan MTB and PNAqPCR assay was 23.1% and 76.9%, respectively. Overall, the sensitivity and specificity of the TaqMan MTB assay for detection of MTBC was 76.9% and 100%, respectively. The PNAqPCR assay had a sensitivity and specificity of 90% and 99.7%, respectively.

Detection of Mycobacterium kansasii Using Amplicons Generated by the COBAS TaqMan MTB System

Detection of Mycobacterium kansasii Using Amplicons Generated by the COBAS TaqMan MTB System

Is Real-Time PCR Better than Conventional PCR for Mycobacterium tuberculosis Complex Detection in Clinical Samples?

Cobas Amplicor MTB and later Cobas TaqMan MTB were used to test a very large series of consecutive specimens received for tuberculosis diagnosis. Performance parameters were estimated and compared overall and for separate specimen categories. Both systems showed excellent specificity, and that of TaqMan was the higher. The sensitivities were similar but satisfactory only with respiratory specimens and smear-positive samples.

Evaluation of Real-time Polymerase Chain Reaction for Detection of the 16S Ribosomal RNA Gene of Mycobacterium tuberculosis and the Diagnosis of Cervical Tuberculous Lymphadenitis in a Country With a High Tuberculosis Incidence

Tuberculous lymphadenitis (TBL) is the most common form of extrapulmonary tuberculosis. Currently, the standard diagnostic test for TBL is culture, which takes more than several weeks to yield results. We studied a real-time polymerase chain reaction (PCR) for rapid detection of Mycobacterium tuberculosis in cervical lymph node specimens obtained from patients in a country where the tuberculosis incidence is high. Patients with cervical lymphadenopathy were prospectively enrolled between April 2009 and March 2010. Clinical specimens obtained through fine-needle aspiration (FNA) and excisional biopsy were tested for M. tuberculosis by the COBAS TaqMan MTB Test, a real-time PCR assay for detecting the 16S ribosomal RNA gene of M. tuberculosis. Mycobacterial culture and histopathological findings from tissue biopsy specimens were used as a reference standard for sensitivity and specificity calculations. Of 73 patients, 41 received a diagnosis of TBL. For biopsy specimens, the sensitivity of real-time PCR was 63.4%, and the specificity was 96.9%. For FNA specimens, the sensitivity was 17.1%, and the specificity was 100%. The sensitivity of real-time PCR of biopsy specimens was comparable to that of tissue culture but significant lower than that of histopathological examination (P < .01). Real-time PCR did not increase the yield for rapid diagnosis of TBL.

Comparison of Two Molecular Methods for Rapid Diagnosis of Extrapulmonary Tuberculosis

Application of real-time PCR for the detection of Mycobacterium tuberculosis enables results to be obtained in about 2 h. A total of 340 nonrespiratory samples were processed using two real-time PCR assay kits: Xpert MTB/RIF and Cobas TaqMan MTB. The sensitivity and specificity of the Xpert assay were 95% and 100%, respectively, compared to 78% and 98% for the Cobas assay.

Removal of PCR Inhibitors in Real-time PCR for Mycobacterium tuberculosis

Background: The inhibition rates for nucleic acid tests of Mycobacterium tuberculosis have been reported to range from less than 1% to more than 10%. Specimen dilution, boiling, addition of bovine serum albumin (BSA), and a silica membrane can be used to override amplification inhibitors in nucleic acid tests of M. tuberculosis. The inhibition rate for real-time PCR of M. tuberculosis (COBAS TaqMan MTB test; Roche Diagnostics, Manheim, Germany) and effective strategies to override PCR inhibitors were investigated in this study. Methods: The inhibition rate for COBAS TaqMan MTB test was investigated in 980 clinical specimens. The effectiveness of PCR inhibitor removal by repeated run, dilution, boiling, addition of BSA, and use of silica membrane were evaluated in the inhibited specimens. Results: Inhibitory substances were present in 4.1% of specimens (40/980). Among 40 inhibited specimens, inhibitory substances were removed in 12 (30%), 30 (75%), 27 (67.5%), 25 (62.5%) and 12 (30%) specimens with repeated run, dilution, addition of RBS, boiling and use of silica membrane, respectively. Conclusion: The overall inhibition rate for the COBAS TaqMan MTB test was 4.1%. Dilution, boiling and addition of BSA were shown to be more effective than repeated run and use of silica membrane for removal of PCR inhibitors. A combination of two methods might be useful and should be studied in the future. (Korean J Clin Microbiol 2011;14:97-102)

Evaluation of the Cobas TaqMan MTB Test for Direct Detection of Mycobacterium tuberculosis Complex in Respiratory Specimens

The Cobas TaqMan MTB test, based on real-time PCR technology, was evaluated for direct detection of Mycobacterium tuberculosis complex (MTBC) in respiratory specimens. A total of 1,093 samples from 446 patients, including 118 acid-fast smear-positive and 975 acid-fast smear-negative specimens, were investigated. Diagnostic cultures performed with 7H11 agar, Löwenstein-Jensen medium, and the Bactec MGIT 960 system were considered the reference methods. When discrepant results between the Cobas TaqMan MTB test and culture occurred, additional results from the BD MGIT TBc identification test and the GenoType Mycobacterium CM test performed on growth-positive and acid-fast-stain-positive MGIT tubes and review of the patient's medical history were used for discrepancy analysis. The overall sensitivity, specificity, positive predictive value, and negative predictive value for the Cobas TaqMan MTB test were 91.5%, 98.7%, 91.5%, and 98.7%, respectively. In general, the performance of the new Cobas TaqMan MTB test was comparable to that of the replaced Cobas Amplicor MTB system. The most prominent feature of the new system was its extraordinarily high sensitivity (79.5%) for detecting MTBC in smear-negative specimens; out of 44 smear-negative but culture-positive specimens, 35 were positive by the new system. The Cobas TaqMan MTB assay, including DNA extraction, can be completed within 3 h.

Evaluation of Cobas TaqMan MTB PCR for Detection of Mycobacterium tuberculosis

Nucleic acid-based amplification tests allow the rapid detection of Mycobacterium tuberculosis. Recently, a real-time PCR assay for M. tuberculosis complex, the Cobas TaqMan MTB test (Roche Diagnostics, Basel, Switzerland), was introduced. We performed a prospective study to evaluate the diagnostic performance of the Cobas TaqMan MTB test system. A total of 406 specimens collected from 247 patients were simultaneously tested by conventional culture, Cobas Amplicor MTB PCR, and TaqMan MTB PCR. The cross-reactivity with other Mycobacterium species and the detection limit were also evaluated. Among 406 specimens, a total of 24 specimens (5.9%) were culture positive: 14 specimens were positive by both TaqMan and Amplicor MTB PCRs, while 5 specimens were positive by only TaqMan PCR. The remaining five specimens were negative by both PCR methods. Seven specimens with negative culture results were positive by TaqMan PCR, but five of these were negative by Amplicor MTB PCR. The sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values were 79.1%, 98.2%, 73.1%, and 98.7% for TaqMan and 58.3%, 99.5%, 87.5%, and 97.4% for the Amplicor MTB PCR test, respectively. There was no cross-reactivity with M. tuberculosis and nontuberculous mycobacterial species. The detection limit for the Cobas TaqMan MTB PCR test was 4.0 copies/μl. The Cobas TaqMan MTB PCR test showed higher sensitivity for detection of the M. tuberculosis complex without disturbing the specificity and NPV than the Amplicor MTB PCR test.