Evaluation of a new commercial assay for diagnosis of pulmonary and nonpulmonary tuberculosis

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.

Amplified Mycobacterium tuberculosis direct test for diagnosing tuberculous pleurisy--a diagnostic accuracy study

BACKGROUND

The study was designed to investigate the clinical usefulness of Amplified Mycobacterium Tuberculosis Direct (AMTD) tests for diagnosing TB pleurisy.

METHODS

One hundred and fifty-two patients for whom the exclusion of tuberculous pleural effusion was necessary were retrospectively analyzed.

RESULTS

The sensitivity of AMTD in diagnosing pleural TB was 36.4% (20 of 55). Combining sputum and pleural effusion AFB smear, pleural biopsy, and AMTD test of pleural effusion increased sensitivity to 82.5% (33/40). There were significantly higher percentages of neutrophils in the pleural effusion in the positive than in the negative AMTD group (38.0 ± 6.7% vs. 11.1 ± 3.7%, p<0.001). Patients with symptom duration <18 days prior to pleural effusion studies had more positive AMTD tests than those with symptom >18 days (70% vs. 31.4%; OR 5.09; 95% CI 1.54-16.79; p = 0.011).

CONCLUSIONS

Combining AMTD tests with conventional diagnostic methods offer good sensitivity for pleural TB diagnosis. Patients in the early course of the disease are better candidates for AMTD tests.

Pseudo-tumoral hepatic tuberculosis discovered after surgical resection

Pseudo-tumoral hepatic tuberculosis is rare. It is characterized by non-specific symptoms and radiological polymorphism. Diagnosis is problematic. This article presents three cases, each clinically different from each other, that illustrate how difficult diagnosis can be. The definitive diagnosis of pseudo-tumoral hepatic tuberculosis was reached on the basis of histo-logical examination of surgical samples. Treatment of the disease based on appropriate anti-tubercular therapy generally gives a positive outcome.

Tuberculous meningitis in Denmark: a review of 50 cases

Background

Tuberculous meningitis is the most severe manifestation of extrapulmonary tuberculosis with a high mortality rate and a high rate of sequelae among survivors. The aim of this study is to assess the current epidemiology, clinical features, diagnostic procedures, treatment and outcome in patients with tuberculous meningitis in Denmark, a country with a low tuberculosis incidence.

Methods

A nationwide retrospective study was conducted, comprising all patients notified with tuberculous meningitis (TBM) in Denmark from 2000-2008. Medical records were reviewed using a standardised protocol.

Results

Fifty patients, including 12 paediatric patients, were identified. 78% of the patients were immigrants from countries of high tuberculosis endemicity. 64% of all patients had a pre-existing immunosuppressive condition; 10% were HIV positive, 48% were HIV seronegative and 42% had an unknown HIV status. Median symptom duration before admission was 14 days in the Danish patient population and 20 days in the immigrant group. Biochemical analysis of cerebrospinal fluid (CSF) samples revealed pleocytosis in 90% with lymphocyte predominance in 66%. Protein levels were elevated in 86%. The most common findings on neuro-radiological imaging were basal meningeal enhancement, tuberculomas and hydrocephalus. Lumbar puncture was performed on 42 patients; 31 of these specimens (74%) had a positive CSF culture for mycobacteria and 9.5% were smear positive for acid-fast bacilli. The overall mortality rate was 19% and 48% of the remaining patients had neurological sequelae of varying degree.

Conclusion

TBM is a rare but severe manifestation of extrapulmonary TB in Denmark. The clinician must be prepared to treat empirically if the suspicion of TBM has arisen to improve treatment outcome.

Clinical evaluation of TRCRapid M.TB for detection of Mycobacterium tuberculosis complex in respiratory and nonrespiratory specimens

The rapid and accurate diagnosis of tuberculosis is crucial to providing optimal treatment and reducing the spread of infection. We evaluated respiratory and nonrespiratory clinical specimens using a new automated Mycobacterium tuberculosis complex (MTBC) rRNA detection kit (TRCRapid M.TB; Tosoh Bioscience, Tokyo, Japan), which is based on the transcription-reverse transcription concerted reaction (TRC). TRC enables the rapid and completely homogeneous real-time monitoring of isothermal RNA sequence amplification without any postamplification procedures. The results were compared with those obtained by M. tuberculosis culture. A total of 1,155 respiratory specimens and 420 nonrespiratory specimens collected from 1,282 patients were investigated. Of the 45 specimens culture positive for MTBC, 42 were TRC positive, and of the 1,530 specimens culture negative for MTBC, 1,523 were TRC negative. Compared to the results of culture, the overall sensitivity and specificity of TRC were 96.6% and 99.9%, respectively, for respiratory specimens and 87.5% and 98.5%, respectively, for nonrespiratory specimens. The sensitivities of TRC were 100% for smear-positive respiratory and nonrespiratory specimens, 88.9% for smear-negative respiratory specimens, and 80% for smear-negative nonrespiratory specimens. No significant differences in test performance between respiratory and nonrespiratory specimens were observed. The TRC method proved to be clinically useful for the rapid identification of MTBC in respiratory and nonrespiratory specimens and in both smear-positive and smear-negative samples.

Detection of Mycobacterium tuberculosis complex organisms in the stools of patients with pulmonary tuberculosis

The laboratory diagnosis of pulmonary tuberculosis mainly relies on the detection of Mycobacterium tuberculosis complex (MTC) organisms in the sputum. In patients who do not give sputum, alternative respiratory tract specimens can be obtained only by invasive procedures. Based on the known survival of MTC organisms in the gastric fluid, we hypothesized that swallowed MTC organisms would be detectable in stool samples. We compared the presence of MTC organisms in respiratory tract specimens and stool specimens collected in parallel from the same patients. MTC was detected in cultures grown on egg-based medium after appropriate decontamination, by microscopic examination after Ziehl–Neelsen staining and by real-time PCR detection of IS6110 using internal controls. A case of pulmonary tuberculosis was defined by the presence of (i) clinical and radiological signs and symptoms suggestive of pulmonary tuberculosis, and (ii) culture of MTC organisms from at least one respiratory tract specimen or (iii) the presence of acid-fast bacilli in the sputum that were subsequently identified as MTC organisms by real-time PCR. The observation of 134 patients suspected to be suffering pulmonary tuberculosis led to the identification of 24 cases and 110 non-infected control patients. Cases and controls did not significantly differ with respect to sex but cases were significantly younger than controls. The sensitivity/specificity was 37.5 %/100 % for the microscopic examination of stools, 54.2 %/100 % for culturing and 100 %/97.3 % for real-time PCR. The positive predicted value was 100 %, 100 % and 88.9 %, respectively, and the negative predicted value was 88 %, 90.9 % and 100 %, respectively. In four patients, a stool specimen initially yielded the correct diagnosis of pulmonary tuberculosis before evaluation of the respiratory tract specimen confirmed the diagnosis. These data indicate that stools could be used in conjunction with sputum testing or as an alternative specimen upon which to base the diagnosis of pulmonary tuberculosis by molecular identification of acid-fast bacilli and culture. This non-invasive alternative procedure is of particular interest for patients who cannot expectorate.

Multidrug-resistant tuberculosis: rapid detection of resistance to rifampin and high or low levels of isoniazid in clinical specimens and isolates

The aim of the present study was to evaluate a new improved multiplex polymerase chain reaction (PCR) hybridisation assay to detect multidrug-resistant tuberculosis. The assay, developed to detect rifampin (rpoB) and isoniazid (katG) gene mutations causing Mycobacterium tuberculosis resistance, was recently extended to include inhA gene mutations that code for low-level isoniazid resistance. Interpretable results were obtained in 115 isolates and in all smear-positive clinical specimens. Rifampin resistance was correctly identified in all specimens and in 20 of 21 (95%) multidrug-resistant isolates compared to BACTEC 460TB. Isoniazid resistance correlated in 18 of 22 (82%) specimens, in 31 of 31 (100%) high-level and 24 of 28 (86%) low-level isoniazid-resistant isolates. The assay was rapid, easy to perform and directly applicable in smear-positive specimens. We predict that the assay may be a useful tool to combat and prevent new cases of multi- and extensively drug-resistant tuberculosis.

Rapid genotypic detection of rifampin- and isoniazid-resistant Mycobacterium tuberculosis directly in clinical specimens

A multiplex PCR DNA strip assay (Genotype MTBDR) designed to detect rifampin (rpoB) and high-level isoniazid (katG) resistance mutations in Mycobacterium tuberculosis isolates was optimized for clinical specimens. Successful genotypic results were achieved with 36 of 38 (95%) smear-positive respiratory specimens, allowing rapid therapeutic adjustments in transmittable drug-resistant tuberculosis.

Current evidence on diagnostic accuracy of commercially based nucleic acid amplification tests for the diagnosis of pulmonary tuberculosis

BACKGROUND

Even though commercial nucleic acid amplification tests (NAATs) have become the most frequently used molecular tests for laboratory diagnosis of pulmonary tuberculosis (TB), published studies report variable estimates of their diagnostic accuracy. We analysed the accuracy of commercial NAATs for the diagnosis of pulmonary TB in smear positive and smear negative respiratory samples using culture as a reference standard.

METHODS

English language studies reporting data sufficient for calculating sensitivity and specificity of commercial NAATs on smear positive and/or smear negative respiratory samples were included. Meta-regression was used to analyse associations with reference test quality, the prevalence of TB, sample and test type. Predictive values for different levels of pre-test probability were quantified using Bayes' approach.

RESULTS

Sixty three journal articles published between 1995 and 2004 met the inclusion criteria. Pooled sensitivity and specificity were 0.96 and 0.85 among smear positive samples and 0.66 and 0.98 among smear negative samples. The number of culture media used as reference test, the inclusion of bronchial samples, and the TB prevalence were found to influence the reported accuracy. The test type had no effect on the diagnostic odds ratio but seemed to be correlated with sensitivity or specificity, probably via a threshold effect.

CONCLUSIONS

Commercial NAATs can be confidently used to exclude TB in patients with smear positive samples in which environmental mycobacteria infection is suspected and to confirm TB in a proportion of smear negative cases. The methodological characteristics of primary studies have a considerable effect on the reported diagnostic accuracy.

[Pseudo-tumoral hepatic tuberculosis developing into a multinodular form despite treatment]

Localized macronodular tuberculosis of the liver is rare. In this location antituberculosis therapy results in a favorable clinical evolution in 100% of cases. We report a pseudo-tumoral form of this condition with no specific clinical, biological or radiological data. After ultrasound guided needle aspiration cytology suggesting metastasis, the correct diagnosis was obtained on liver biopsy after laparotomy. After what was probably inadequate therapy, the enlargement of several hepatic and splenic macronodules was observed. After two years and eight months, the clinical condition of the patient was good but radiological features remained. The risk of diagnostic errors and the therapeutic difficulties in the zones where the incidence of tuberculosis is low should be noted.

The Clinical Utility of Polymerase Chain Reaction for the Diagnosis of Pleural Tuberculosis

BACKGROUND

There is no exact consensus about the usefulness of the Mycobacterium tuberculosis polymerase chain reaction (PCR) testing for the diagnosis of tuberculous pleural effusion because of the diverse PCR methods and the different diagnostic criteria that are described in other studies.

METHODS

We analyzed pleural effusion specimens obtained from 111 patients for whom the exclusion of the possibility of tuberculous pleural effusion was necessary. We performed M. tuberculosis PCR testing using the Cobas Amplicor MTB test (Roche Diagnostic Systems), which is fully automated and commercially available.

RESULTS

Results of the M. tuberculosis PCR test of pleural effusion specimens were positive for 7 (17.1%) of the 41 patients with confirmed pleural tuberculosis and for 3 (18.8%) of the 16 patients with probable pleural tuberculosis. The overall sensitivity and specificity of M. tuberculosis PCR testing of pleural effusion were 17.5% and 98.1%, respectively. The sensitivity of M. tuberculosis PCR testing for each group of patients with tuberculous pleural effusion detected by smear-positive results, smear-negative and culture-positive results, and culture-negative and pleural biopsy-positive results, was 100.0%, 33.3%, and 3.7%, respectively. Of the 57 patients with pleural tuberculosis, only 3 (5.3%) had positive results of M. tuberculosis PCR testing along with negative results of smearing, negative results of pleural pathological analysis, and a low level of adenosine deaminase.

CONCLUSION

For specimens such as pleural effusion, in which the bacillary load is very low, the clinical utility of PCR testing seems highly limited.

Comparison of the COBAS AMPLICOR MTB and BDProbeTec ET assays for detection of Mycobacterium tuberculosis in respiratory specimens

The performances of the BDProbeTec ET (Becton Dickinson) and COBAS AMPLICOR MTB (Roche) were retrospectively evaluated for detecting Mycobacterium tuberculosis complex in various respiratory specimens. The BACTEC and MGIT liquid culture system (Becton Dickinson) was used as a reference method. A total of 824 respiratory specimens, comprised of sputa, bronchoalveolar lavage fluid, and bronchial and tracheal aspirates from 580 patients, were evaluated. Out of 824 clinical specimens, 109 specimens from 43 patients were culture positive for M. tuberculosis. Of these 109 specimens, 67 were smear positive, 85 were positive by the COBAS AMPLICOR MTB test, and 94 were positive by the BDProbeTec ET. Of the 715 culture-negative specimens, 17 were positive by the auramine staining, 11 were positive by the COBAS AMPLICOR MTB test, and 12 were positive by the BDProbeTec ET. After discrepancy analysis and review of the patients' clinical data, 130 specimens from 50 patients were considered "true-positive" specimens. This resulted in the following sensitivities: microscopy, 61.5%; COBAS AMPLICOR MTB test, 78.0%; and BDProbeTec ET, 86.2%. The specificities of each system, based on the clinical diagnosis, were 99.7% for microscopy, 99.9% for the COBAS AMPLICOR MTB test, and 99.9% for the BDProbeTec ET. The data presented represent a considerable number of specimens evaluated with a considerable number of culture- and auramine-positive and culture-positive and auramine-negative results and therefore give a realistic view of how the data should be interpreted in a daily routine situation. Specifically, the data with regard to the culture-positive and auramine-negative specimens are useful, because in a routine situation, auramine-negative specimens are sometimes accepted, on clinical indications, to be analyzed by an amplification method.

Detection of Mycobacterium tuberculosis complex in formalin-fixed, paraffin-embedded tissue specimens with necrotizing granulomatous inflammation by strand displacement amplification

Rapid, reliable diagnosis of tuberculosis is essential to initiate correct treatment, avoid severe complications, and prevent transmission. Conventional microbiological methods may not be an option if samples are formalin-fixed and paraffin-embedded (FFPE) for histopathological examination. With the demonstration of necrotizing granulomatous inflammation, tuberculosis becomes an important differential diagnosis, although it was not initially suspected. Following paraffin extraction, BDProbeTec ET strand displacement amplification for detection of Mycobacterium tuberculosis complex (MTC) was applied to 47 prospectively and 19 retrospectively collected FFPE samples from various sources with granulomatous inflammation and results were compared to tuberculosis notification. Of the prospective samples, 20 were from patients who were notified as having tuberculosis and the assay was positive in 18 (90%). Specificity was 100%. For 27 of the patients with prospectively collected FFPE specimens, culture was performed on a specimen collected at a later date from the same location. Culture revealed MTC in 14 and nontuberculous mycobacteria in four. BDProbeTec ET was positive in 13 (92.8%) of the patients with positive MTC culture and negative in the remaining. The sensitivity and specificity in 19 archival samples was 40% and 100%, respectively, compared to notification data. The assay provided rapid, correct diagnosis on different sources of FFPE samples collected prospectively and therefore offers an important supplementary method for patients where tuberculosis was not initially suspected.

Comparison of the real-time PCR method and the Gen-Probe amplified Mycobacterium tuberculosis direct test for detection of Mycobacterium tuberculosis in pulmonary and nonpulmonary specimens

Real-time PCR was compared to Amplified Mycobacterium tuberculosis Direct Test (AMTDII) for 100 clinical specimens. The overall sensitivities of the real-time PCR method and AMTDII were similar for respiratory and nonrespiratory specimens. However, real-time PCR seemed to be less susceptible to amplification inhibitors than AMTDII.

Improved sensitivity of nucleic acid amplification for rapid diagnosis of tuberculous meningitis

Early diagnosis of tuberculous meningitis (TBM) is essential for a positive outcome; but present microbiological diagnostic techniques are insensitive, slow, or laborious. We evaluated the standard BDProbeTec ET strand displacement amplification method (the standard ProbeTec method) for the detection of Mycobacterium tuberculosis complex organisms in parallel with the ProbeTec method with a modified pretreatment procedure with 101 prospectively collected cerebrospinal fluid specimens from 94 patients with suspected TBM. By the modified method, the sample-washing step was omitted. A definitive diagnosis was attained by culture. Thirteen specimens from 12 patients were culture positive for M. tuberculosis complex organisms; three specimens (23%) were microscopy positive for acid-fast bacilli. Among the culture-positive specimens, the standard ProbeTec method was positive for 8 (61.5%) and the modified assay was positive for 10 (76.9%). The overall specificity by both procedures was 98.8% compared to the results of culture. After discrepancy analysis, conducted by reviewing the patients' previous laboratory data, the specificity increased to 100%. If the cutoff value for respiratory specimens was adjusted from the recommended value of 3,400 to 1,000, the sensitivity of the modified procedure increased to 84.7%, with unchanged specificity. Results were obtained in 3 to 4 h. The new pretreatment procedure with the ProbeTec assay described here provides a rapid, simple, and sensitive tool for the diagnosis of TBM.

Clinical evaluation of the semiautomated BDProbeTec ET System for the detection of Mycobacterium tuberculosis in respiratory and nonrespiratory specimens

The reliability of the BDProbeTec ET assay, a semiautomated system for the direct detection of Mycobacterium tuberculosis complex in clinical specimens was evaluated by comparing results obtained by the system to those obtained by conventional culture methods and clinical data of the patients. Out of 1131 (735 respiratory and 396 nonrespiratory) specimens, 42 were smear- and 125 culture-positive. After resolution of discrepant results the overall sensitivity, specificity, and positive and negative predictive values for the BDProbeTec ET assay were 90.3, 96.9, 78.3, and 98.9%, respectively. For smear-positive specimens, all values were 100%, while the values for smear-negative specimens were 86.1, 96.9, 70.1, and 98.8%, respectively. All 28 nontuberculous mycobacteria were negative with the BDProbeTec ET system. The data demonstrate that the BDProbeTec ET assay is a highly sensitive and specific technique for the rapid (within 5 h) detection of M. tuberculosis complex in respiratory and nonrespiratory specimens.

Comparison of the BDProbeTec ET system with the roche COBAS AMPLICOR System for detection of Mycobacterium tuberculosis complex in the respiratory and pleural fluid specimens

The new BDProbeTec ET System (BDET; BD Biosciences, Sparks, MD) was compared with the Roche COBAS AMPLICOR System (CAS) and culture for Mycobacterium tuberculosis (MTB). A total of 253 specimens (152 respiratory and 101 pleural fluid specimens) collected from 240 patients were tested in parallel with the 3 assays. After resolving the discrepancies, the sensitivity, specificity, and positive and negative predictive values of the BDET for detecting MTB was 76.9%, 93.7%, 71.4%, and 95.2% for the respiratory specimens and 88.9%, 92.4%, 53.3%, and 98.8% for the pleural fluid specimens, respectively. The corresponding values of the CAS were 69.2%, 100%, 100%, and 94% for the respiratory specimens and 33.3%, 100%, 100%, and 93.9% for the pleural fluid specimens, respectively. No significant differences in sensitivities were observed between the results of both assays for the respiratory specimens. However, statistically significant differences in sensitivities were found between the BDET and CAS for the pleural fluid specimens (P =.02). Although the BDET was less specific than the CAS (P =.007), the BDET has an excellent sensitivity for detecting MTB in the pleural fluid specimens. Considering the low sensitivity of other available tests, the BDET can be a useful diagnostic tool for excluding MTB, particularly in the pleural fluid specimens.

Evaluation of the BDProbeTec ET system as screening tool in the direct detection of mycobacterium tuberculosis complex in respiratory specimens

We evaluated the BDProbeTec ET System (Becton Dickinson) for the routine detection of Mycobacterium tuberculosis complex (MTC) in respiratory specimens and pleural fluids, comparing with microscopy (Ziehl Neelsen stain, ZN) and culture in liquid (BACTEC MGIT 960, MGIT) and solid (Löwenstein Jensen, LJ) media. Five hundred and two specimens, collected from 266 patients, of which 257 with suspected tuberculosis and 9 receiving anti-tuberculosis treatment, were investigated. Thirty-nine specimens were positive by any method, including false positives. Mycobacteria were isolated from 33 specimens (32 Mycobacterium tuberculosis and 1 Mycobacterium chelonae). Thirty-six specimens were BDProbeTec ET positive, 33 specimens were MGIT positive, 27 were LJ positive and 22 were ZN positive. With BDProbeTec ET, 2 specimens were false negative (culture positive), and 2 specimens from non-treated patients were false positive (culture negative). The overall sensitivity, specificity, and positive and negative predictive values for BDProbeTec ET compared to culture were 93.7, 98.7, 83.3, and 99.5%, respectively, while with smear-positive and smear-negative specimens the sensitivities were 100% and 81.5% respectively. In five treated patients the disappearance of MTC could be monitored using BDProbeTec ET in parallel with culture. The overall inhibition rate was 0.2%. BDProbeTec ET can be very useful for rapid detection of MTC, especially in smear-negative respiratory specimens.

Comparison of the BDProbeTec ET system with the Cobas Amplicor PCR for direct detection of Mycobacterium tuberculosis in respiratory samples

In the study presented here, the performance of the BDProbeTec ET system (Becton Dickinson, USA) was compared with the Roche Cobas Amplicor-PCR (Roche, Switzerland) to detect Mycobacterium tuberculosis complex (MTB) in clinical respiratory samples. The Bactec MGIT 960 liquid culture system (Becton Dickinson) was used as a reference method. A total of 411 samples were tested. Of the 93 culture-positive samples, both the BDProbeTec ET system and the Cobas Amplicor-PCR detected 87 (sensitivity, 93.5%). When only smear-negative samples were considered, the BDProbeTec ET exhibited a sensitivity of 50% and the Cobas Amplicor-PCR 60%. Specificity was 99.7% for the BDProbeTec ET system and 100% for the Cobas Amplicor-PCR. Percent agreement between the two nucleic amplification methods was 98.7%. Inhibition occurred in three (0.7%) samples in the BDProbeTec ET system. The high sensitivity and specificity of the BDProbeTec ET system suggest it is a useful method for the rapid and direct detection of MTB in smear-positive respiratory samples.

Evaluation of the BDProbeTec ET system for direct detection of Mycobacterium tuberculosis in pulmonary and extrapulmonary samples: a multicenter study

We evaluated the BDProbeTec ET system (Becton Dickinson, Sparks, Md.), a strand displacement amplification-based technique, for direct detection of Mycobacterium tuberculosis in 867 clinical samples. Of 294 extrapulmonary specimens, 52 had positive results by both BDProbeTec ET and culture and 209 had negative results by both methods; sensitivity and specificity were 76.5 and 95.9%, respectively. After resolution of discrepancies, the sensitivity rose to 77.8%.