Rapid detection of pulmonary tuberculosis using the BDProbeTEC ET Mycobacterium tuberculosis Complex Direct Detection Assay (DTB)

Performance of the BD ProbeTec ET direct detection assay for the analysis of Mycobacterium tuberculosis in respiratory and non-respiratory clinical specimens

Objectives

Early detection of Mycobacterial tuberculosis infection (MTB) is pivotal for the treatment of tuberculosis (TB).

Background

This study was performed to evaluate the performance of BD ProbeTec ET direct detection assay (DTB) against the gold standard culture technique for confirmation of MTB infection.

Methods

A total of 266 consecutive and non-duplicate clinical specimens for detection of MTB were included in this study. There were 118 respiratory and 148 non-respiratory samples. All samples were tested by microscopy for acid-fast bacillus (AFB), MTB culture and biochemical identification with simultaneous testing by DTB.

Results

A total of 88 samples (33%) were culture-positive for MTB including 39/118 respiratory, 29/99 fluid and 20/49 tissue samples. DTB sensitivity for respiratory samples was 97% and specificity was 96% with a positive predictive value (PPV) of 93% and negative predictive value (NPV) of 99%. Sensitivity of DTB in fluid samples was 80%, specificity 88%, PPV 69% and NPV 93% whereas sensitivity of DTB for tissue samples was 25%, specificity 90%, PPV 63% and NPV 63%. Of the 50 (56.8%) smear-positive samples, DTB sensitivity was 100% for respiratory, 85% for fluid and 100% for tissue samples.

Conclusion

DTB performed within acceptable limits for the rapid detection of MTB in respiratory samples compared to fluid and tissue specimens.

Performance assessment of the CapitalBio mycobacterium identification array system for identification of mycobacteria

The CapitalBio Mycobacterium identification microarray system is a rapid system for the detection of Mycobacterium tuberculosis. The performance of this system was assessed with 24 reference strains, 486 Mycobacterium tuberculosis clinical isolates, and 40 clinical samples and then compared to the "gold standard" of DNA sequencing. The CapitalBio Mycobacterium identification microarray system showed highly concordant identification results of 100% and 98.4% for Mycobacterium tuberculosis complex (MTC) and nontuberculous mycobacteria (NTM), respectively. The sensitivity and specificity of the CapitalBio Mycobacterium identification array for identification of Mycobacterium tuberculosis isolates were 99.6% and 100%, respectively, for direct detection and identification of clinical samples, and the overall sensitivity was 52.5%. It was 100% for sputum, 16.7% for pleural fluid, and 10% for bronchoalveolar lavage fluid, respectively. The total assay was completed in 6 h, including DNA extraction, PCR, and hybridization. The results of this study confirm the utility of this system for the rapid identification of mycobacteria and suggest that the CapitalBio Mycobacterium identification array is a molecular diagnostic technique with high sensitivity and specificity that has the capacity to quickly identify most mycobacteria.

Combination of molecular assay and clinical evaluation for early confirmation of tuberculosis cases

The cost-effectiveness of the ProbeTec ET Direct TB assay (DTB) was compared with that of culture for detection of Mycobacterium tuberculosis complex in 361 acid-fast stain-positive respiratory specimens. The overall sensitivity, specificity, positive predictive value and negative predictive value of DTB were 97.7%, 86.6%, 87.2% and 97.6%, respectively. When clinical evaluation was added to DTB, the specificity and positive predictive value of DTB increased to 94.7% and 95.4%, respectively. Treatment costs of $133,521 would have been saved in this cohort if DTB, instead of culture results, had been used to eliminate 'false-positive' smear results.

Performance assessment of the Capilia TB assay and the BD ProbeTec ET system for rapid culture confirmation of Mycobacterium tuberculosis

Because of the increasing numbers of nontuberculous mycobacterial isolates from clinical specimens, rapid and accurate methods for culture confirmation of Mycobacterium tuberculosis are urgently needed. The study evaluated the performance of the Capilia TB immunochromatographic assay (TAUNS, Numazu, Japan) for culture confirmation of M. tuberculosis using 242 culture-positive liquid media in 2 mycobacterial laboratories from November 2005 to February 2006. Among the 242 samples, 183 were also tested with the BD ProbeTec ET (CTB) assay (Becton Dickinson, Sparks, MD). The results of both assays were compared to the culture results and to each other. The overall sensitivity and specificity of the Capilia TB assay were 98.6% and 97.9%, respectively, and for the CTB assay were 97.3% and 97.1%, respectively. The positive and negative predictive values for the Capilia TB assay were 98.6% and 97.9%, respectively, and for the CTB assay were 98.2% and 95.8%, respectively. Among the 183 samples tested with both assays, 8 had discrepant results, including Capilia-TB-false-positive in 2, CTB-false-positive in another 2, CTB-false-negative in 2, Capilia TB-false-negative in 1, and both assays with false-negative results in the remaining one. This study demonstrated that the Capilia TB assay has a similar diagnostic value with the CTB assay. In addition, with the immunochromatographic method, it is less time-consuming and does not require other laboratory equipment.

Use of a disposable water filter for prevention of false-positive results due to nontuberculosis mycobacteria in a clinical laboratory performing routine acid-fast staining for tuberculosis

A point-of-use 0.2-microm filter was evaluated for elimination of nontuberculosis mycobacteria in laboratory water to reduce false-positive acid-fast bacillus staining results. Use of the point-of-use filter can significantly reduce the false-positive rate to 1.2% compared to samples treated with tap water (10.7%) and deionized water (8.7%).

Performance assessment of the DR. MTBC Screen assay and the BD ProbeTec ET system for direct detection of Mycobacterium tuberculosis in respiratory specimens

The performance of the DR. MTBC PCR-based assay and the BD ProbeTec ET Mycobacterium tuberculosis Complex Direct Detection (DTB) assay for the direct detection of Mycobacterium tuberculosis was evaluated using 1,066 consecutive clinical respiratory samples collected from 494 patients who did not have old cases of pulmonary tuberculosis and were not receiving antituberculosis treatment at National Taiwan University Hospital from January to February 2005. The results of both assays were compared to the "gold standard" of combined culture results and clinical diagnosis. The overall sensitivity and specificity of the DR. MTBC Screen assay were 56.6% and 98.9%, respectively, and of the DTB assay were 63.2% and 98.4%, respectively. The positive and negative predictive values for the DR. MTBC Screen assay were 84.5% and 95.4%, respectively, and for the DTB assay were 81.7% and 96.0%, respectively. The DR. MTBC Screen assay produced 11 false-positive results for 11 patients, including three samples yielding non-M. tuberculosis mycobacteria (one each for M. abscessus, a mixture of M. abscessus and M. chelonae, and unidentified non-tuberculosis mycobacteria). The DTB assay produced 15 false-positive results for 13 patients, including five samples from four patients yielding non-tuberculosis mycobacteria (two for M. abscessus, one for a mixture of M. abscessus and M. chelonae, and two for unidentified non-tuberculosis mycobacteria). This study demonstrated that the DR. MTBC Screen assay has a similar diagnostic value but fewer false-positive results than the DTB assay for respiratory specimens.

A review of tuberculosis: reflections on the past, present and future of a global epidemic disease

Tuberculosis remains the leading cause of death worldwide from a single infectious organism. Approximately 32% of the world's population is infected and an estimated two million people die annually from this treatable disease. Over the past 50 years, with medical treatment and standard public health practices, tuberculosis diminished in developed countries and resulted in a loss of interest and funding for research in improving diagnostic and treatment options. In developing countries, efforts including BCG vaccination have failed to control tuberculosis and the disease continues to spread as the world becomes more globalized. At the same time, multidrug resistant tuberculosis has emerged, challenging even the most advance treatment centers. Better diagnostic techniques, control measures and treatment options are desperately needed but advances require worldwide commitment to battle this age-old disease.

Performance assessment of a nested-PCR assay (the RAPID BAP-MTB) and the BD ProbeTec ET system for detection of Mycobacterium tuberculosis in clinical specimens

The performance of a nested PCR-based assay (the RAPID BAP-MTB; AsiaGen, Taichung, Taiwan) and the BD ProbeTec ET (DTB) system (Becton Dickinson, Sparks, Md.) for detection of Mycobacterium tuberculosis was evaluated with 600 consecutive clinical samples. These samples, including 552 respiratory specimens and 48 nonrespiratory specimens, were collected from 333 patients treated at National Taiwan University Hospital from September to October 2003. The results of both assays were compared to the gold standard of combined culture results and clinical diagnosis. The overall sensitivity and specificity of the RAPID BAP-MTB assay for respiratory specimens were 66.7% and 97.2%, respectively, and for the DTB assay they were 56.7% and 95.3%, respectively. The positive and negative predictive values for the RAPID BAP-MTB were 74.1% and 96.0%, respectively, and for the DTB assay they were 59.6% and 94.7%, respectively. For smear-negative samples, the sensitivity of the RAPID BAP-MTB and DTB assays was 57.1% and 40.5%, respectively. The RAPID BAP-MTB assay produced 14 false-positive results in 14 samples, including one of the six samples yielding Mycobacterium abscessus, one of the six samples yielding Mycobacterium avium intracellulare, one sample from a patient with a history of pulmonary tuberculosis with complete treatment, and three samples from three patients with a previous diagnosis of tuberculosis who were under treatment at the time of specimen collection. Among the 48 nonrespiratory specimens, the RAPID BAP-MTB assay was positive in one biopsy sample from a patient with lumbar tuberculous spondylitis and one pus sample from a patient with tuberculous cervical lymphadenopathy. Our results showed that the RAPID BAP-MTB assay is better than the DTB assay for both respiratory specimens and nonrespiratory specimens. The overall time for processing this assay is only 5 h. In addition, its diagnostic accuracy in smear-negative samples is as high as in smear-positive samples.