Polymerase Chain Reaction for Mycobacterium tuberculosis

Rapid detection of Mycobacterium tuberculosis using a novel ultrafast chip-type real-time polymerase chain reaction system

BACKGROUND

NBS LabChip G2-3 is a novel, ultrafast, chip-type portable real-time polymerase chain reaction (PCR) system. We evaluated the clinical usefulness of this system in detecting pulmonary TB and assessed its diagnostic performance compared with a conventional tube-type PCR system.

METHODS

A total of 247 sputum samples were collected from patients suspected of having pulmonary TB. After the decontamination process, these samples were examined by fluorescence staining for acid-fast bacilli, cultures with both solid and liquid media, and real-time PCR with the NBS LabChip and a conventional tube-type system. The diagnostic accuracy of the NBS LabChip system and the agreement between the two assays were evaluated.

RESULTS

Considering mycobacterial culture results as a gold standard, the overall sensitivity and specificity of the NBS LabChip was 83.8% (95% CI, 73.8%-91.1%) and 94.0% (95% CI, 89.3%-97.1%), respectively. For the detection of TB from the smear-positive samples, the sensitivity and specificity of the NBS LabChip was 96.0% (95% CI, 86.3%-99.5%) and 83.3% (95% CI, 72.3%-95.7%), respectively. For the smear-negative samples, the sensitivity and specificity of the NBS LabChip was 63.3% (95% CI, 43.9%-80.1%) and 95.0% (95% CI, 90.4%-97.8%), respectively. There were no significant differences in the sensitivity and specificity between the NBS LabChip and a conventional tube-type system, although the NBS LabChip shortened the PCR time (27 min for 45 cycles).

CONCLUSIONS

The NBS LabChip G2-3 system has potential as an ultrafast, cost-effective diagnostic tool for pulmonary TB with high sensitivity and specificity.

A persistent case of tuberculosis of the pubic symphysis and pubic bone

A case of a patient suffering from tuberculosis of the pubic symphysis and pubic bone is presented. There were no symptoms other than pain in the right groin area for 12 months. An X-ray of the pelvis showed an osteodestructive lesion of the pubic bone, and an MRI revealed an abscess formation of the pubic symphysis. Tissue samples were collected via CT-guided needle biopsy. Histological evaluation of tissue and analysis by PCR prompted the diagnosis of musculoskeletal tuberculosis. Despite antituberculous chemotherapy according to the current guidelines, the osteodestructive lesion progressed. This case highlights the difficulty of treating bone infections in general. Moreover, Mycobacterium tuberculosis as a rare causative agent of bone infections is discussed.

The diagnostic accuracy of tuberculosis real-time polymerase chain reaction analysis of computed tomography-guided bronchial wash samples

We evaluated the diagnostic accuracy of real-time polymerase chain reaction (RT-PCR) analysis of bronchoscopic wash specimens obtained using computed tomography (CT) guidance for diagnosis of pulmonary tuberculosis (TB) patients who were unable to produce sputum samples or were sputum smear-negative. Data from patients who had lesions likely to be pulmonary TB on CT images were analyzed retrospectively. Twenty-seven patients (23.1%) were diagnosed with definite pulmonary TB, and 72 patients (61.5%) were classified as not having TB. The sensitivity, specificity, positive predictive value, and negative predictive value of RT-PCR were 0.78 (95% CI, 0.57-0.91), 0.93 (95% CI, 0.84-0.97), 0.81 (95% CI, 0.60-0.93), and 0.92 (95% CI, 0.82-0.97), respectively. We concluded that most of the sputum-smear negative TB cases could be diagnosed microbiologically or ruled out rapidly and accurately by RT-PCR analysis of bronchial wash fluid.

Unilateral lower lung field opacities on chest radiography: a comparison of the clinical manifestations of tuberculosis and pneumonia

BACKGROUND

The radiological manifestations of lower lung field (LLF) tuberculosis (LLFTB) are similar to those of LLF pneumonia (LLFP), making diagnosis challenging. The aim of this study was to determine if there are differences in the clinical manifestations of LLFTB and LLFP in patients with unilateral LLF opacities.

METHODS

We performed a retrospective review of patient records to identify those with unilateral LLF opacities who were subsequently diagnosed with LLFTB or LLFP. We compared demographics, clinical manifestations, hematological data, and radiographic findings between the groups of patients.

RESULTS

We identified 22 and 72 patients diagnosed with LLFTB and LLFP, respectively. Multivariate analysis revealed that age (odds ratio [OR]=1.05, 95% confidence interval [CI]=0.99-1.11, P=0.072), lack of fever>38°C (OR=9.04, 95% CI=1.69-48.40, P=0.001), duration of symptoms≥7 days (OR=4.57, 95% CI=1.09-19.26, P=0.038), and the lack of air bronchograms upon radiography (OR=12.08, 95% CI=1.98-73.64, P=0.007) were significant predictors of LLFTB in patients with LLF opacities. We used these predictors to construct a mathematical model for predicting LLFTB in patients with LLF opacities.

CONCLUSIONS

Our findings suggest that older age, prolonged duration of symptoms, lack of fever>38°C, and the absence of air bronchograms are more common in patients with LLFTB than patients with LLFP. These findings may help clinicians differentiate between LLFTB and LLFP and thus initiate timely and appropriate treatment.

Comparison of acid-fast stain and culture for Mycobacterium tuberculosis in pre- and post-bronchoscopy sputum and bronchoalveolar lavage in HIV-infected patients with atypical chest X-ray in Ethiopia

BACKGROUND:

Smear-negative tuberculosis occurs more frequently in human immunodeficiency virus (HIV)-infected patients than in non-HIV-infected patients. Besides, there are substantial numbers of patients who cannot produce sputum, making the diagnosis of pulmonary tuberculosis (PTB) difficult.

AIMS:

To evaluate the relative yield of pre- and post-bronchoscopy sputum and bronchoalveolar lavage (BAL) in ‘sputum smear’-negative, HIV-positive patients.

SETTINGS:

A tertiary care referral hospital in Addis Ababa.

MATERIALS AND METHODS:

Acid-fast stain (AFS) using the concentration technique was done on 85 pre-bronchoscopy sputum and 120 BAL samples. Direct AFS was done on all BAL and 117 post-bronchoscopy sputum samples. Culture for Mycobacterium tuberculosis (MTB) was done for all sputa and BAL.

RESULTS:

MTB was isolated from 26 (21.7%), 23 (19.7%) and 13 (15.3%) of BAL, post- and pre-bronchoscopy sputum cultures respectively. AFS on pre-bronchoscopy sputum using concentration technique and direct AFS on BAL together detected 11 (41%) of the 27 culture-positive cases. In patients who could produce sputum, the sensitivity of pre-bronchoscopy sputum culture (13/85, 15.3%) was comparable to BAL (12/85, 14%) and post-bronchoscopy sputum (12/85, 14%). In patients who could not produce sputum, however, both BAL (12/35, 40%) and post-bronchoscopy sputum (12/32, 31.4%) detected significantly more patients than those who could produce sputum (P=0.002, P=0.028 respectively).

CONCLUSION:

In HIV-infected patients, AFS by concentration method on pre-bronchoscopy sputum and direct AFS on BAL in patients who cannot produce sputum are the preferred methods of making a rapid diagnosis. BAL culture seems to add little value in patients who can produce sputum; therefore, bronchoscopy should be deferred under such circumstances.

Rapid differential diagnosis between extrapulmonary tuberculosis and focal complications of brucellosis using a multiplex real-time PCR assay

BACKGROUND

Arduous to differ clinically, extrapulmonary tuberculosis and focal complications of brucellosis remain important causes of morbidity and mortality in many countries. We developed and applied a multiplex real-time PCR assay (M RT-PCR) for the simultaneous detection of Mycobacterium tuberculosis complex and Brucella spp.

METHODOLOGY

Conventional microbiological techniques and M RT-PCR for M. tuberculosis complex and Brucella spp were performed on 45 clinical specimens from patients with focal complications of brucellosis or extrapulmonary tuberculosis and 26 control samples. Fragments of 207 bp and 164 bp from the conserved region of the genes coding for an immunogenic membrane protein of 31 kDa of B. abortus (BCSP31) and the intergenic region SenX3-RegX3 were used for the identification of Brucella and M. tuberculosis complex, respectively.

CONCLUSIONS

The detection limit of the M RT-PCR was 2 genomes per reaction for both pathogens and the intra- and inter-assay coefficients of variation were 0.44% and 0.93% for Brucella and 0.58% and 1.12% for Mycobacterium. M RT-PCR correctly identified 42 of the 45 samples from patients with tuberculosis or brucellosis and was negative in all the controls. Thus, the overall sensitivity, specificity, PPV and NPV values of the M RT PCR assay were 93.3%, 100%, 100% and 89.7%, respectively, with an accuracy of 95.8% (95% CI, 91.1%-100%). Since M RT-PCR is highly reproducible and more rapid and sensitive than conventional microbiological tests, this technique could be a promising and practical approach for the differential diagnosis between extrapulmonary tuberculosis and focal complications of brucellosis.

Utility of high-resolution computed tomography for predicting risk of sputum smear-negative pulmonary tuberculosis

BACKGROUND

To diagnose sputum smear-negative pulmonary tuberculosis (PTB) is difficult and the ability of high-resolution computed tomography (HRCT) for diagnosing PTB has remained unclear in the sputum smear-negative setting. We retrospectively investigated whether or not this imaging modality can predict risk for sputum smear-negative PTB.

METHODS

We used HRCT to examine the findings of 116 patients with suspected PTB despite negative sputum smears for acid-fast bacilli (AFB). We investigated their clinical features and HRCT-findings to predict the risk for PTB by multivariate analysis and a combination of HRCT findings by stepwise regression analysis. We then designed provisional HRCT diagnostic criteria based on these results to rank the risk of PTB and blinded observers assessed the validity and reliability of these criteria.

RESULTS

A positive tuberculin skin test alone among clinical laboratory findings was significantly associated with an increase of risk of PTB. Multivariate regression analysis showed that large nodules, tree-in-bud appearance, lobular consolidation and the main lesion being located in S1, S2, and S6 were significantly associated with an increased risk of PTB. Stepwise regression analysis showed that coexistence of the above 4 factors was most significantly associated with an increase in the risk for PTB. Ranking of the results using our HRCT diagnostic criteria by blinded observers revealed good utility and agreement for predicting PTB risk.

CONCLUSIONS

Even in the sputum smear-negative setting, HRCT can predict the risk of PTB with good reproducibility and can select patients having a high probability of PTB.

PCR colorimetric dot-blot assay and clinical pretest probability for diagnosis of Pulmonary Tuberculosis in smear-negative patients

BACKGROUND

Smear-negative pulmonary tuberculosis (SNPTB) accounts for 30% of Pulmonary Tuberculosis (PTB) cases reported annually in developing nations. Polymerase chain reaction (PCR) may provide an alternative for the rapid detection of Mycobacterium tuberculosis (MTB); however little data are available regarding the clinical utility of PCR in SNPTB, in a setting with a high burden of TB/HIV co-infection.

METHODS

To evaluate the performance of the PCR dot-blot in parallel with pretest probability (Clinical Suspicion) in patients suspected of having SNPTB, a prospective study of 213 individuals with clinical and radiological suspicion of SNPTB was carried out from May 2003 to May 2004, in a TB/HIV reference hospital. Respiratory specialists estimated the pretest probability of active disease into high, intermediate, low categories. Expectorated sputum was examined by direct microscopy (Ziehl-Neelsen staining), culture (Lowenstein Jensen) and PCR dot-blot. Gold standard was based on culture positivity combined with the clinical definition of PTB.

RESULTS

In smear-negative and HIV subjects, active PTB was diagnosed in 28.4% (43/151) and 42.2% (19/45), respectively. In the high, intermediate and low pretest probability categories active PTB was diagnosed in 67.4% (31/46), 24% (6/25), 7.5% (6/80), respectively. PCR had sensitivity of 65% (CI 95%: 50%-78%) and specificity of 83% (CI 95%: 75%-89%). There was no difference in the sensitivity of PCR in relation to HIV status. PCR sensitivity and specificity among non-previously TB treated and those treated in the past were, respectively: 69%, 43%, 85% and 80%. The high pretest probability, when used as a diagnostic test, had sensitivity of 72% (CI 95%:57%-84%) and specificity of 86% (CI 95%:78%-92%). Using the PCR dot-blot in parallel with high pretest probability as a diagnostic test, sensitivity, specificity, positive and negative predictive values were: 90%, 71%, 75%, and 88%, respectively. Among non-previously TB treated and HIV subjects, this approach had sensitivity, specificity, positive and negative predictive values of 91%, 79%, 81%, 90%, and 90%, 65%, 72%, 88%, respectively.

CONCLUSION

PCR dot-blot associated with a high clinical suspicion may provide an important contribution to the diagnosis of SNPTB mainly in patients that have not been previously treated attended at a TB/HIV reference hospital.

TB in a low-incidence country: differences between new immigrants, foreign-born residents and native residents

BACKGROUND

New immigrants and foreign-born residents add to the burden of pulmonary tuberculosis (TB) in low-incidence countries. The highest TB rates have been found among recent immigrants. Active screening programs are likely to change the clinical presentation of TB, but the extent of the difference between immigrant and resident populations has not been studied prospectively.

METHODS

Adult new immigrants were screened upon entry to 1 of 5 immigration centers in Switzerland. Immigrants with abnormal chest radiographs were enrolled and compared in a cohort study to consecutive admitted foreign-born residents from moderate-to-high incidence countries and native residents presenting with suspected TB.

RESULTS

Of 42,601 new immigrants screened, 112 had chest radiographs suspicious for TB. They were compared with foreign-born residents (n=118) and native residents (n=155) with suspected TB (n=385 patients included). Active TB was confirmed in 40.5% of all patients (immigrants 38.4%, foreign-born residents 50%, native residents 34.8%). Clinical signs and symptoms of TB and laboratory markers of inflammation were significantly less common in immigrants than in the other groups with normal results in >70%. The proportion of positive results on rapid testing to detect M. tuberculosis (MTB) in 3 respiratory specimens was significantly lower in immigrants (34.9% for acid-fast staining; 55.8% for polymerase chain reaction) compared with foreign-born residents (76.2% and 89.1%, respectively) and native residents (83.3% and 90.9%, respectively). Isoniazid resistance and multi-drug resistance were more prevalent in immigrants.

CONCLUSION

New immigrants with TB detected in a screening program are often asymptomatic and have a low yield of rapid diagnostic tests but are at higher risk for resistant MTB strains. Postmigration follow-up of pulmonary infiltrates is essential in order to control TB among immigrants, even in the absence of clinical and laboratory signs of infection.

[Diagnostics for pulmonary tuberculosis in adults]

The incidence of pulmonary tuberculosis (TB) is decreasing in Western Europe. However, TB should not be considered to be a rare disease, particularly in immigrants and in immunocompromised persons (i.e. HIV infection). The clinical presentation is often atypical in immunocompromised persons. In general, the extent of the disease is underestimated by the clinical presentation. X-ray and a sequential investigation of three samples of sputum including microscopy, culture and susceptibility testing for the first-line drugs should be obtained. Tuberculin testing is useful in the diagnosis of latent TB and in screening persons with close contact to patients with active disease. New blood tests based on the detection of interferon-g released by antigen specific T-cells have some advantages compared to tuberculin testing.

The Use of Real-Time Polymerase Chain Reaction for Rapid Diagnosis of Skeletal Tuberculosis

We identified Mycobacterium tuberculosis DNA using real-time polymerase chain reaction on a specimen from an osteolytic lesion of a femoral condyle, in which the frozen section demonstrated granulomas. The process was much more rapid than is possible with culture. The rapid detection of M tuberculosis and the concomitant exclusion of granulomatous disease caused by nontuberculous mycobacteria or systemic fungi are necessary to appropriately treat skeletal tuberculosis. The detection and identification of M tuberculosis by culture may require several weeks using traditional methods. The real-time polymerase chain reaction method used has been shown to be rapid and reliable, and is able to detect and differentiate both tuberculous and nontuberculous mycobacteria. Real-time polymerase chain reaction may become a diagnostic standard for the evaluation of clinical specimens for the presence of mycobacteria; this case demonstrates the potential utility of this assay for the rapid diagnosis of skeletal tuberculosis.

The diagnosis of tuberculosis

Diagnostic testing for tuberculosis has remained unchanged for nearly a century, but newer technologies hold the promise of a true revolution in tuberculosis diagnostics. New tests may well supplant the tuberculin skin test in diagnosing latent tuberculosis infection in much of the world. Tests such as the nucleic acid amplification assays allow more rapid and accurate diagnosing of pulmonary and extrapulmonary tuberculosis. The appropriate and affordable use of any of these tests depends on the setting in which they are employed.