Diagnosis of pulmonary tuberculosis using PCR assays on sputum collected within 24 hours of hospital admission

Performance of Nucleic Acid Amplification Tests in Patients with Presumptive Pulmonary Tuberculosis in Taiwan

INTRODUCTION

Several nucleic acid amplification tests (NAATs) for detection of Mycobacterium tuberculosis (TB) complex (MTBC) are available in Taiwan; however, their performances may differ and have not been extensively evaluated. Therefore, we aimed to explore the accuracy of NAATs overall followed by comparison between platforms commonly used in Taiwan.

METHODS

This study enrolled presumptive pulmonary TB patients with NAATs throughout Taiwan. The diagnostic performance of smear microscopy and NAATs was assessed using sputum culture as a reference standard. To investigate the performance of NAATs in excluding non-tuberculous mycobacteria (NTM), we quantified the false-positive proportion of NAATs in patients infected with NTM.

RESULTS

Of the 4126 enrollees, 860 (20.8%) had positive NAATs. The sensitivity and specificity of NAATs were 83.2% and 96.7%, respectively, compared to 81.5% and 55.3% for smear. There was no significant difference in sensitivity between the NAATs and smear; however, the specificity of smear was significantly lower than that of the NAATs [difference 41.4%, 95% confidence interval (CI) 39.6-43.2%]. There was no significant difference in sensitivity among Roche Cobas Amplicor Mycobacterium tuberculosis assay (Amplicor), Xpert MTB/RIF assay (Xpert) and in-house polymerase chain reaction (in-house PCR) (82.2% versus 83.8% versus 82.4%); however, in-house PCR was significantly less specific than Amplicor (difference 5.3%, 95% CI 2.4-8.2%) and Xpert (difference 5.8%, 95% CI 3.1-8.5%). The sensitivity of NAATs among smear-negative cases was 33.1% (95% CI 26.0-40.3%). In-house PCR had a significantly higher false-positive rate among specimens that were culture positive for NTM than Amplicor (7.7% versus 0.3%; difference 7.4%, 95% CI 3.4-11.5%) and Xpert (7.7% versus 0.7%; difference 7.0%, 95% CI 2.9-11.0%).

CONCLUSION

The NAATs overall had a relatively high sensitivity and specificity in detecting MTBC while Amplicor and Xpert performed better than in-house PCR in excluding NTM. Our findings will be useful for the development of national policy.

Pneumonia caused by Mycobacterium tuberculosis

Tuberculosis (TB) is one of the top ten leading causes of death worldwide. The causative agent of TB is Mycobacterium tuberculosis. Acute tuberculous pneumonia (TP) is an acute form of pulmonary TB. However, acute TP and non-tuberculous community-acquired pneumonia can be easily confused, resulting in deterioration of TP due to delayed treatment. Therefore, rapid and accurate diagnosis of acute TP is crucial in order to stop the transmission of TB. Moreover, development of new diagnostic tools (technologies and approaches), and flexible application of different therapy schemes will help to reduce the incidence of TP and promote the goal of ending the TB epidemic.

Performance and Utilization of a Laboratory-Developed Nucleic Acid Amplification Test (NAAT) for the Diagnosis of Pulmonary and Extrapulmonary Tuberculosis in a Low-Prevalence Area

OBJECTIVES

Tuberculosis (TB) is a significant global health problem. In low-prevalence areas and low clinical suspicion, nucleic acid amplification tests (NAAT) for direct detection of Mycobacterium tuberculosis complex (MTBC) can speed therapy initiation and infection control. An NAAT assay (TBPCR) targeting MTBC IS6110 is used for detecting MTBC in our low-prevalence population.

METHODS

Fifteen-year review of patient records identified 146 patients with culture-positive pulmonary tuberculosis (PTB) or extrapulmonary tuberculosis (EPTB). Laboratory-developed TBPCR was retrospectively compared with standard stain and cultures for PTB and EPTB diagnoses.

RESULTS

TBPCR assay was used in 57% of patients with PTB and 33% of patients with EPTB. TBPCR detected 88.4% of all TB (smear-positive, 97%; smear-negative, 79%) with 100% specificity. Low bacterial load was indicated in TBPCR-negative PTB (P = .002) and EPTB (P < .008).

CONCLUSIONS

TBPCR performance was optimum but significantly underused. Guidelines are proposed for mandated use of TBPCR that capture patients with clinically suspected PTB. Focused TBPCR use in low prevalence populations will benefit patient care, infection prevention, and public health.

Diagnostic Yield of Fluorescence and Ziehl-Neelsen Staining Techniques in the Diagnosis of Pulmonary Tuberculosis: A Comparative Study in a District Health Facility

Background

Despite the recent advancement in diagnostic methods, the smear microscopy remains the gold standard for the diagnosis of pulmonary tuberculosis in high burden countries like Ghana. Notwithstanding, fluorescence staining technique provides a more efficient option for the detection of Mycobacterium tuberculosis positive smears. This study therefore aimed at assessing the diagnostic performance of fluorescence microscopy (FM) and Ziehl-Neelsen (ZN) staining techniques in the diagnosis of pulmonary tuberculosis.

Methods

A comparative study was carried out on 100 patients who reported at the Out Patients Department (OPD) or the Directly Observed Therapy (DOT) center of the Kade Government Hospital and were suspected of having pulmonary tuberculosis. Two (2) sputum samples each were collected. This included one spot and one morning sample. The smears were prepared and stained with FM and ZN staining techniques. Xpert MTB/RIF assay was also performed.

Results

Of the 200 samples analyzed, 71 (35.5%), 46 (23.0%), and 84 (42.0%) were positive for pulmonary tuberculosis when FM, ZN, and XPERT MTB/RIF assays were used, respectively. The mean reading time of FM was three times faster than the ZN technique with very good acceptance (1.5min: 4.6min). The sensitivity and specificity of fluorescent staining to that of XPERT MTB/RIF assay were 84.5% and 100%, respectively, while those of ZN staining were 54.8% and 100%, respectively.

Conclusion

For a routine laboratory test in a resource-limited setting, our study has demonstrated that fluorescence staining technique is a more sensitive test for the diagnosis of pulmonary tuberculosis as compared to the conventional ZN technique.

Predictors of Initial Smear-Negative Active Pulmonary Tuberculosis with Acute Early Stage Lung Injury by High-Resolution Computed Tomography and Clinical Manifestations: An Auxiliary Model in Critical Patients

This study evaluated the diagnostic use of high-resolution computed tomography (HRCT), chest X-ray (CXR), and clinical manifestations (CM) to identify initial smear-negative (iSN) active pulmonary tuberculosis (aPTB) [iSN-aPTB] in patients with iSN-pulmonary diseases (PD) and acute lung injury (ALI). In the derivation cohort, the [iSN-PD] with ALI patients were divided into the [iSN-aPTB] (G1, n = 26) and [non-aPTB-PD] (G2, n = 233) groups. Lung morphology, number, and lobar (segmental) distribution were evaluated using CXR and HRCT. A multivariate analysis was performed to identify independent variables associated with G1, which were used to generate predictive score models for G1. The predictive model was validated in a separate population of patients (n = 372) with [iSN-PD] and (ALI). The validated model for [HRCT (CXR + Hypoalbuminemia)] had 93.5% (25.8%) sensitivity, 99.5% (89.4%) specificity, and a negative predictive value of 99.5% (93.0%). For [iSN-aPTB], the post-test probability in the derivation cohort (prevalence = 10%), validation cohort (prevalence = 8.3%), and the given prevalence (prevalence = 1%) was 88.7%, 94.4%, and 41.5%, respectively. The HRCT model effectively identified the [iSN-aPTB] subjects among the [iSN-PD] with ALI, regardless of CM. The [non-aPTB-PD] were also correctly classified by the HRCT and [CXR + Hypoalbuminemia] models.

A mode of error: Immunoglobulin binding protein (a subset of anti-citrullinated proteins) can cause false positive tuberculosis test results in rheumatoid arthritis

Citrullinated Immunoglobulin Binding Protein (BiP) is a newly described autoimmune target in rheumatoid arthritis (RA), one of many cyclic citrullinated peptides(CCP or ACPA). BiP is over-expressed in RA patients causing T cell expansion and increased interferon levels during incubation for the QuantiFERON-Gold tuberculosis test (QFT-G TB). The QFT-G TB has never been validated where interferon is increased by underlying disease, as for example RA. Of ACPA-positive RA patients (n = 126), we found a 13% false-positive TB test rate by QFT-G TB. Despite subsequent biologic therapy for 3 years of all 126 RA patients, none showed evidence of TB without INH. Most of the false-positive RA patients after treatment with biologic therapy reverted to a negative QFT-G test. False TB tests correlated with ACPA level (p < 0.02). Three healthy women without arthritis or TB exposure had negative QFT-G TB. In vitro, all three tested positive every time for TB correlating to the dose of BiP or anti-BiP added, at 2 ug/ml, 5 ug/ml, 10 ug/ml, and 20 ug/ml. BiP naturally found in the majority of ACPA-positive RA patients can result in a false positive QFT-G TB. Subsequent undertreatment of RA, if biologic therapy is withheld, and overtreatment of presumed latent TB may harm patients.

Combination of commercially available molecular assays and culture based methods in diagnosis of tuberculosis and drug resistant tuberculosis

Early diagnosis of tuberculosis is of major clinical importance. Among 4733 clinical specimens collected from 3363 patients and subjected to Ziehl–Neelsen microscopy, 4109 were inoculated onto Löwenstein–Jensen slants and 3139 in Bactec/9000MB. Polymerase Chain Reaction (PCR) was performed in 3139 specimens, whereas, a genotypic assay was directly applied in 93 Mycobacterium tuberculosis complex PCR-positive for isoniazid and rifampicin resistance detection specimens (GenoType MTBDRplus). Recovered M. tuberculosis isolates (64) as well as, 21 more sent from Regional Hospitals were tested for antimycobacterial resistance with a phenotypic (manual MGIT-SIRE) and a genotypic assay (GenoType MTBDRplus). PCR in the clinical specimens showed excellent specificity (97.4%) and accuracy (96.8%), good sensitivity (70.4%), but low positive predictive value (40.3%). MGIT-SIRE performed to M. tuberculosis did not confer a reliable result in 16 isolates. Of the remaining 69 isolates, 15 were resistant to streptomycin, seven to isoniazid, seven to ethambutol and five to rifampicin. GenoType MTBDRplus correctly detected isoniazid (seven) and rifampicin-resistant M. tuberculosis strains (five), showing an excellent performance overall (100%). Susceptibility results by the molecular assay applied directly to clinical specimens were identical to those obtained from recovered isolates of the corresponding patients. Combining molecular and conventional methods greatly contribute to early diagnosis and accurate susceptibility testing of tuberculosis.

The effectiveness of real-time PCR assay, compared with microbiologic results for the diagnosis of pulmonary tuberculosis

Background

The incidence of tuberculosis (TB) in Korea is relatively high compared to the other Organisation for Economic Co-operation and Development (OECD) countries, with a prevalence of 71 per 100,000 in 2012, although the incidence is declining. Real-time polymerase chain reaction (PCR) has been introduced for the rapid diagnosis of TB. Recently, its advantage lies in higher sensitivity and specificity for the diagnosis of TB. This study evaluated the clinical accuracy of real-time PCR using respiratory specimens in a clinical setting.

Methods

Real-time PCR assays using sputum specimens and/or bronchoscopic aspirates from 2,877 subjects were reviewed retrospectively; 2,859 subjects were enrolled. The diagnosis of TB was determined by positive microbiology, pathological findings of TB in the lung and pleura, or clinical suspicion of active TB following anti-TB medication for more than 6 months with a favorable response.

Results

Sensitivity, specificity, and accuracy were 44%, 99%, and 86% from sputum, and 65%, 97%, and 87% from bronchoscopic aspirates, respectively. For overall respiratory specimens, sensitivity was 59%, specificity was 98%, and accuracy increased to 89%.

Conclusion

Positivity in real-time PCR using any respiratory specimens suggests the possibility of active TB in clinically suspected cases, guiding to start anti-TB medication. Real-time PCR from selective bronchoscopic aspirates enhances the diagnostic yield much more when added to sputum examination.

Successful diagnosis of tuberculous lymphadenitis by loop-mediated isothermal amplification of cutaneous samples from an ulcerated surface lesion: a case report

INTRODUCTION

Tuberculous lymphadenitis is the most frequent form of extrapulmonary tuberculous. Although nucleic acid amplification assays such as polymerase chain reaction have recently become mainstream techniques for diagnosing tuberculous lymphadenitis, they are still not routinely performed in developing countries because of their high costs and complicated procedures.

CASE PRESENTATION

We describe a case of tuberculous lymphadenitis in a 79-year-old Japanese man who had been on continuous hemodialysis for end-stage renal disease. We employed loop-mediated isothermal amplification and the procedure for ultrarapid extraction to develop a fast and easy-to-perform procedure for diagnosing tuberculous lymphadenitis.

CONCLUSIONS

The commercially available loop-mediated isothermal amplification assay kit and a rapid purification procedure enabled us to identify and amplify a Mycobacterium tuberculosis-specific gene within just 1.5 hours.

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.

Comparison of two laboratory-developed PCR methods for the diagnosis of pulmonary tuberculosis in Brazilian patients with and without HIV infection

BACKGROUND

Direct smear examination with Ziehl-Neelsen (ZN) staining for the diagnosis of pulmonary tuberculosis (PTB) is cheap and easy to use, but its low sensitivity is a major drawback, particularly in HIV seropositive patients. As such, new tools for laboratory diagnosis are urgently needed to improve the case detection rate, especially in regions with a high prevalence of TB and HIV.

OBJECTIVE

To evaluate the performance of two in house PCR (Polymerase Chain Reaction): PCR dot-blot methodology (PCR dot-blot) and PCR agarose gel electrophoresis (PCR-AG) for the diagnosis of Pulmonary Tuberculosis (PTB) in HIV seropositive and HIV seronegative patients.

METHODS

A prospective study was conducted (from May 2003 to May 2004) in a TB/HIV reference hospital. Sputum specimens from 277 PTB suspects were tested by Acid Fast Bacilli (AFB) smear, Culture and in house PCR assays (PCR dot-blot and PCR-AG) and their performances evaluated. Positive cultures combined with the definition of clinical pulmonary TB were employed as the gold standard.

RESULTS

The overall prevalence of PTB was 46% (128/277); in HIV+, prevalence was 54.0% (40/74). The sensitivity and specificity of PCR dot-blot were 74% (CI 95%; 66.1%-81.2%) and 85% (CI 95%; 78.8%-90.3%); and of PCR-AG were 43% (CI 95%; 34.5%-51.6%) and 76% (CI 95%; 69.2%-82.8%), respectively. For HIV seropositive and HIV seronegative samples, sensitivities of PCR dot-blot (72% vs 75%; p=0.46) and PCR-AG (42% vs 43%; p=0.54) were similar. Among HIV seronegative patients and PTB suspects, ROC analysis presented the following values for the AFB smear (0.837), Culture (0.926), PCR dot-blot (0.801) and PCR-AG (0.599). In HIV seropositive patients, these area values were (0.713), (0.900), (0.789) and (0.595), respectively.

CONCLUSION

Results of this study demonstrate that the in house PCR dot blot may be an improvement for ruling out PTB diagnosis in PTB suspects assisted at hospitals with a high prevalence of TB/HIV.

Intensive tuberculosis screening for HIV-infected patients starting antiretroviral therapy in Durban, South Africa

BACKGROUND

The World Health Organization (WHO) recommends cough as the trigger for tuberculosis screening in human immunodeficiency virus (HIV)-infected patients, with acid-fast bacillus (AFB) smear as the initial diagnostic test. Our objective was to assess the yield and cost of a more intensive tuberculosis screening in HIV-infected patients starting antiretroviral therapy (ART) in Durban, South Africa.

METHODS

We prospectively enrolled adults, regardless of tuberculosis signs/symptoms, who were undergoing ART training from May 2007 to May 2008. After the symptom screen, patients expectorated sputum for AFB smear, tuberculosis polymerase chain reaction (PCR), and mycobacterial culture. Sensitivity and specificity of different symptoms and tests, alone and in combination, were compared with the reference standard of 6-week tuberculosis culture results. Program costs included personnel, materials, and cultures.

RESULTS

Of 1035 subjects, 487 (59%) were female; median CD4 cell count was 100 cells/microL. A total of 210 subjects (20%) were receiving tuberculosis treatment and were excluded. Of the remaining 825 subjects, 158 (19%) had positive sputum cultures, of whom 14 (9%) had a positive AFB smear and 82 (52%) reported cough. The combination of cough, other symptoms, AFB smear, and chest radiograph had 93% sensitivity (95% confidence interval, 88%-97%) and 15% specificity (95% confidence interval, 13%-18%). The incremental cost of intensive screening including culture was $360 per additional tuberculosis case identified.

CONCLUSIONS

Nearly 20% of patients starting ART in Durban, South Africa, had undiagnosed, culture-positive pulmonary tuberculosis. Despite WHO recommendations, neither cough nor AFB smear were adequately sensitive for screening. Tuberculosis sputum cultures should be performed before ART initiation, regardless of symptoms, in areas with a high prevalence of HIV and tuberculosis.

Tuberculosis of the breast

Tuberculosis of the breast is an uncommon disease even in countries where the incidence of pulmonary and extrapulmonary tuberculosis is high. Clinical presentation is usually of a solitary, ill-defined, unilateral hard lump situated in the upper outer quadrant of the breast. This disease can present a diagnostic problem on radiological and microbiological investigations, and thus a high index of suspicion is needed. Incorporating a highly sensitive technique like polymerase chain reaction (PCR) may be helpful in establishing the usefulness of such technology and can aid in conforming the diagnosis early. The disease is curable with antitubercular drugs, and surgery is rarely required

Endobronchial ultrasound increases the diagnostic yields of polymerase chain reaction and smear for pulmonary tuberculosis

OBJECTIVES

Our objective was to determine the contribution of endobronchial ultrasound in the diagnostic yields of acid-fast bacillus smear, nucleic acid amplification tests, and culture in bronchoalveolar lavage fluid for pulmonary tuberculosis.

METHODS

During a 1-year interval, 99 patients who had initial sputum-negative acid-fast bacillus smears or no sputum but were later proven to have a positive culture for Mycobacterium tuberculosis in their sputum or bronchoalveolar lavage fluid were retrospectively studied. Among them, 56 patients underwent bronchoscopy with endobronchial ultrasound (EBUS group) and 43 patients received conventional bronchoscopy for bronchoalveolar lavage (non-EBUS group).

RESULTS

The diagnostic yields of the nucleic acid amplification tests (89.3%, 50/56; P = .006), acid-fast bacillus smear (30.4%, 17/56; P = .013), and M tuberculosis culture in bronchoalveolar lavage fluid (67.9%, 38/56; P = .041) were significantly higher in the EBUS group of patients. The results of those who underwent conventional bronchoscopy were 65.1% (28/43), 9.3% (4/43), and 46.5% (20/43), respectively. Combining bronchoalveolar lavage fluid smear and nucleic acid amplification tests, we made a rapid diagnosis of pulmonary tuberculosis in 51 (91.1%) of the 56 EBUS patients and 29 (67.4%; P = .004) of the 43 non-EBUS patients.

CONCLUSIONS

The introduction of endobronchial ultrasound increases the diagnostic yield of the nucleic acid amplification tests, acid-fast bacillus smear, and M tuberculosis culture from bronchioalveolar lavage fluid in patients with pulmonary tuberculosis who have negative sputum smear or no sputum production.

PCR and Elisa methods (IgG and IgM): their comparison with conventional techniques for diagnosis of Mycobacterium tuberculosis

In order to establish a rapid and stable method for diagnosis of Mycobacterium tuberculosis infection and minimize the side effects of delayed diagnosis on patients and health system, a cross sectional study was carried out. Since, the infection rate with this bacteria increasing and one of the reasons for this increase is long process of laboratory identification, therefore establishing new diagnosis methods could decrease disease rate. To achieve this aim, collected sputum and blood specimens from 50 patients with clinical suspicion of pulmonary tuberculosis were studied with both traditional, acid-fast stain (AFB) and culture method compare to Enzyme-linked immunosorbent assay (Elisa) (IgG and IgM) and Polymerase Chain Reaction (PCR) methods. The sensitivity and specificity of all methods were determined by using the PCR results as the gold standard. The overall sensitivity, specificity, positive predictive value and negative predictive value of AFB were 17.64, 100, 100 and 70.12%. These values for culture method was 29.41, 100, 100 and 73.33% and for IgG antibody were 66.7, 81.81, 64.7 and 81.81% and IgM antibody were 70.58, 90.9, 80 and 85.71%, respectively. It was concluded that maximum sensitivity and specificity can be achieved by PCR method.

Urine as an adjunct specimen for the diagnosis of active pulmonary tuberculosis

BACKGROUND

The diagnosis of pulmonary tuberculosis (PTB) is conventionally established by examination of three Ziehl-Neelsen stained smears; however, negative results do not preclude active TB. Since tubercle bacilli or their nucleic acids are also expected to be excreted through the kidneys, we assessed spot urine as a supplementary specimen for diagnosing PTB.

METHODS

A total of 164 respiratory specimens (147 sputum, 15 bronchoalveolar lavage, and two gastric lavage) from 81 suspected PTB cases were prospectively collected and processed. A total of 112 non-TB controls were also included in the study. For three consecutive days, morning urine specimens were collected from all patients and controls, and were processed for culture by BACTEC MGIT 960 (mycobacteria growth indicator tube) and Lowenstein-Jensen methods and for PCR by amplifying a 441-bp fragment of the hsp65 gene (Mycobacterium genus-specific) and a 786-bp fragment of the cfp32 gene (TB complex-specific).

RESULTS

Of the 81 patients suspected of having PTB, 46 (56.8%) were sputum culture-positive. Of these, 12 (26.1%) were also urine culture-positive for Mycobacterium tuberculosis. Of the 35 sputum culture-negative cases, three (8.6%) were urine culture-positive. The TB complex specific PCR (cfp32) was positive in 52.2% (24/46) of the bacteriologically-confirmed and 28.6% (10/35) of the bacteriologically-negative PTB patients. In none of the control subjects were urine culture or PCR found to be positive for M. tuberculosis.

CONCLUSIONS

Specific PCR and culture examination of spot urine samples from suspected PTB patients significantly improved the detection rate of PTB and should be encouraged in resource-limited settings and where multiple pulmonary specimens are not feasible.

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.

Métodos convencionais e moleculares para o diagnóstico da tuberculose pulmonar: um estudo comparativo

OBJETIVO: Comparar quatro métodos laboratoriais no diagnóstico de tuberculose pulmonar. MÉTODOS: Foram realizadas pesquisa direta pelas colorações de Ziehl-Neelsen e auramina, cultura para micobactérias em meio Löwenstein-Jensen (LJ) e polymerase chain reaction (PCR, reação em cadeia da polimerase) para Mycobacterium tuberculosis em 160 amostras de secreção respiratória de pacientes com suspeita de tuberculose pulmonar. As cepas isoladas foram identificadas por método radiométrico utilizando-se p-nitro-alfa-acetilamino-beta-hidroxipropiofenona (NAP) e métodos clássicos. A sensibilidade dos métodos foi comparada com o padrão ouro para o diagnóstico da tuberculose pulmonar, definido por critérios clínicos, radiológicos e microbiológicos. RESULTADOS: Dos 160 pacientes, 142 foram diagnosticados com tuberculose pulmonar de acordo com o padrão ouro. As técnicas de Ziehl-Neelsen e auramina, cultura em meio LJ e PCR apresentaram sensibilidade de 54,2%, 58,4%, 67,6% e 77,5%, respectivamente, quando comparados ao critério diagnóstico adotado. A especificidade dos quatro métodos foi de 100%. A concordância na identificação da micobactéria entre PCR e o método radiométrico utilizando NAP foi alta (96,8%). A sensibilidade da PCR foi de 50,8% nas amostras com baciloscopia negativa e de 98,8% naquelas com baciloscopia positiva. Nas amostras com resultados negativos na baciloscopia e cultura, a sensibilidade da PCR foi menor que nas com resultados positivos (25,6% e 99,0%, respectivamente). CONCLUSÕES: A PCR é método promissor no diagnóstico da tuberculose pulmonar, mesmo em amostras paucibacilares. Além disso, apresenta a vantagem da identificação simultânea e rapidez do resultado.

Comparison of in-house PCR with conventional techniques and Cobas Amplicor M. tuberculosis kit for detection of Mycobacterium tuberculosis

PURPOSE

Polymerase chain reaction (PCR) assay, introduced as a fast and sensitive diagnostic method, is useful in detecting Mycobacterium tuberculosis. The purpose of this study was to evaluate the usefulness of in-house PCR assay in the detection of Mycobacterium tuberculosis by comparing PCR results with conventional diagnostic techniques and Cobas Amplicor M. tuberculosis kit.

MATERIALS AND METHODS

We retrospectively assessed the diagnostic yield of in-house PCR method employed for the amplification IS6110 sequences in 2,973 specimens. We also compared in-house PCR with Cobas Amplicor M. tuberculosis kit in 120 specimens collected from June to July 2006. Routine acid-fast stain (AFS) and culture assay were also performed and analyzed.

RESULTS

Of 2,973 cases, 2,832 cases (95.3%) showed consistent results between in house PCR, AFS and culture methods, whereas 141 (4.7%) displayed inconsistent results. The sensitivities, specificities, and positive and negative predictive values of each method were as follows: 77.5%, 99.7%, 95.5%, and 98.0%, respectively for PCR; 49.2%, 100%, 100%, and 95.7%, respectively, for AFS method; and 80.7%, 100%, 100%, and 98.3%, respectively, for culture assay. Consistent results between PCR and Cobas Amplicor M. tuberculosis kit were shown in 109 cases (90.8%). The sensitivities, specificities, and positive and negative predictive values of each method were as follows: 81.3%, 98.9%, 96.3%, and 93.5% respectively for PCR and 71.9%, 100%, 100%, and 90.7%, respectively, for Cobas Amplicor kit.

CONCLUSION

In-house PCR and Cobas Amplicor kit show high sensitivity and specificity, and are reliable tests in the diagnosis of tuberculosis.

Commercial nucleic-acid amplification tests for diagnosis of pulmonary tuberculosis in respiratory specimens: meta-analysis and meta-regression

Background

Hundreds of studies have evaluated the diagnostic accuracy of nucleic-acid amplification tests (NAATs) for tuberculosis (TB). Commercial tests have been shown to give more consistent results than in-house assays. Previous meta-analyses have found high specificity but low and highly variable estimates of sensitivity. However, reasons for variability in study results have not been adequately explored. We performed a meta-analysis on the accuracy of commercial NAATs to diagnose pulmonary TB and meta-regression to identify factors that are associated with higher accuracy.

Methodology/Principal Findings

We identified 2948 citations from searching the literature. We found 402 articles that met our eligibility criteria. In the final analysis, 125 separate studies from 105 articles that reported NAAT results from respiratory specimens were included. The pooled sensitivity was 0.85 (range 0.36–1.00) and the pooled specificity was 0.97 (range 0.54–1.00). However, both measures were significantly heterogeneous (p<.001). We performed subgroup and meta-regression analyses to identify sources of heterogeneity. Even after stratifying by type of commercial test, we could not account for the variability. In the meta-regression, the threshold effect was significant (p = .01) and the use of other respiratory specimens besides sputum was associated with higher accuracy.

Conclusions/Significance

The sensitivity and specificity estimates for commercial NAATs in respiratory specimens were highly variable, with sensitivity lower and more inconsistent than specificity. Thus, summary measures of diagnostic accuracy are not clinically meaningful. The use of different cut-off values and the use of specimens other than sputum could explain some of the observed heterogeneity. Based on these observations, commercial NAATs alone cannot be recommended to replace conventional tests for diagnosing pulmonary TB. Improvements in diagnostic accuracy, particularly sensitivity, need to be made in order for this expensive technology to be worthwhile and beneficial in low-resource countries.

[Prevention of tuberculosis in care settings]

INTRODUCTION

The hospital is a favourable setting for the transmission of tubercle bacilli. The presence of susceptible subjects, often immunocompromised, increases the dangers. This risk extends to the patients' visitors and to the staff. It is therefore the responsibility of the hospital to establish preventative measures capable of reducing the risk of transmission or to reduce the effects by appropriate management of exposed subjects.

BACKGROUND

The modes and vectors of transmission are well established. The standardised prevention of transmission is achieved by isolation, the indications and duration of which are based on incomplete information. The surveillance of the carers by the doctor in charge, is based on precise recommendations depending on the risk of exposure.

VIEWPOINT

The objectives are a reduction diagnostic delay, a better determination of infectivity and its duration during treatment, and a more complete census of cases of hospital acquired tuberculosis.

CONCLUSIONS

The management of tuberculosis in hospital requires co-ordination of all involved including those outside the institution and a deliberate policy in the institution itself.

Molecular diagnostics in tuberculosis

Molecular diagnostics in tuberculosis has enabled rapid detection of Mycobacterium tuberculosis complex in clinical specimens, identification of mycobacterial species, detection of drug resistance, and typing for epidemiological investigation. In the laboratory diagnosis of tuberculosis, the nucleic acid amplification (NAA) test is rapid and specific but not as sensitive as culture of mycobacteria. The primary determinant of successful NAA testing for tuberculosis depends on the shedding of mycobacterial DNA in secretions from caseating granulomas and its dissemination into sterile body fluids or tissue biopsies. In multibacillary diseases with a high mycobacterial load, a positive Ziehl-Neelsen smear with a positive NAA test is diagnostic of active tuberculosis, whereas a positive Ziehl-Neelsen smear with a negative NAA test in the absence of inhibitors would indicate nontuberculous mycobacterial disease. The role of the NAA test is more important in paucibacillary diseases with low mycobacterial loads. The presence of polymerase chain reaction (PCR) inhibitors, however, especially in extrapulmonary specimens, may produce false-negative results. Although this problem can be overcome to some extent by extra extraction steps, the additional processing invariably leads to the loss of mycobacterial DNA. To circumvent this problem, a brief culture augmentation step is carried out before the NAA test is performed, which can enhance the mycobacterial load while concomitantly diluting inhibitors, thereby maintaining the sensitivity of the test without excessively increasing turnaround time.

Clinical suspicion as a primary guidance to use commercial amplification tests for rapid diagnosis of pulmonary tuberculosis

The Abbott LCx (Abbott Park, IL) Mycobacterium tuberculosis complex is a commercial amplification assay discontinued from the European market in 2002. A prospective clinical study was carried out to evaluate the clinical utility of the above test as applied by specialists for the rapid diagnosis of active pulmonary tuberculosis (PTB). According to the physician's clinical judgment, patients were classified into 3 groups (low, intermediate, and high) aiming to estimate the probability of active disease. The gold standard for final diagnosis was based on microbiologic and clinical information including data from a 6-month follow-up period. Sensitivities and specificities of rapid microbiologic tests were compared with those based on an integrated approach including clinical evaluation plus the above tests. The incidence of PTB in 214 patients was 13.1%. The basis for initial treatment of PTB was smear-positive results in 46%, positive LCx results in 29%, and clinical suspicion in 18%. For the remaining 7%, therapy was started upon receipt of culture results. The sensitivity, specificity, and positive and negative predictive values of the LCx assay were 68%, 99%, 95%, and 95%, respectively. In comparison, they were 93%, 99%, 96%, and 99%, respectively, for the combination of clinical evaluation plus the LCx test. It is concluded that in patients with high-to-moderate pretest probabilities, the combination of clinical judgment and amplification results strongly enhances a rapid and correct diagnosis of PTB.

In-house nucleic acid amplification tests for the detection of Mycobacterium tuberculosis in sputum specimens: meta-analysis and meta-regression

BACKGROUND

More than 200 studies related to nucleic acid amplification (NAA) tests to detect Mycobacterium tuberculosis directly from clinical specimens have appeared in the world literature since this technology was first introduced. NAA tests come as either commercial kits or as tests designed by the reporting investigators themselves (in-house tests). In-house tests vary widely in their accuracy, and factors that contribute to heterogeneity in test accuracy are not well characterized. Here, we used meta-analytical methods, including meta-regression, to identify factors related to study design and assay protocols that affect test accuracy in order to identify those factors associated with high estimates of accuracy.

RESULTS

By searching multiple databases and sources, we identified 2520 potentially relevant citations, and analyzed 84 separate studies from 65 publications that dealt with in-house NAA tests to detect M. tuberculosis in sputum samples. Sources of heterogeneity in test accuracy estimates were determined by subgroup and meta-regression analyses. Among 84 studies analyzed, the sensitivity and specificity estimates varied widely; sensitivity varied from 9.4% to 100%, and specificity estimates ranged from 5.6% to 100%. In the meta-regression analysis, the use of IS6110 as a target, and the use of nested PCR methods appeared to be significantly associated with higher diagnostic accuracy.

CONCLUSION

Estimates of accuracy of in-house NAA tests for tuberculosis are highly heterogeneous. The use of IS6110 as an amplification target, and the use of nested PCR methods appeared to be associated with higher diagnostic accuracy. However, the substantial heterogeneity in both sensitivity and specificity of the in-house NAA tests rendered clinically useful estimates of test accuracy difficult. Future development of NAA-based tests to detect M. tuberculosis from sputum specimens should take into consideration these findings in improving accuracy of in-house NAA tests.

Response to Empirical Anti-Tuberculosis Treatment in Patients with Sputum Smear-Negative Presumptive Pulmonary Tuberculosis

BACKGROUND

In many cases, physicians initiate anti-tuberculosis (TB) treatment based only on symptoms or radiographic findings without confirmation of pulmonary TB by acid-fast bacilli (AFB) smear. It has not been well known which clinical characteristics could be used as predictors for positive culture or real TB in patients with sputum smear-negative presumptive pulmonary TB.

OBJECTIVE

We tried to elucidate treatment outcomes in patients with sputum smear-negative presumptive pulmonary TB and to find predictors of positive culture results.

METHODS

We reviewed data of the patients who had been treated as presumptive TB with negative AFB smear on the basis of clinical and radiographic features from December 1998 to December 2000 at a university hospital in Korea. We reviewed medical records and radiographs of patients and analyzed possible predictors for positive culture.

RESULTS

One hundred and one patients were enrolled. Among them, pulmonary TB was confirmed by culture in 32 patients (31%). Thirty-one (96.9%) out of 32 culture-positive patients showed clinical or radiographic improvement as did 50 (72.5%) out of 69 culture-negative patients. The predictor for a positive culture result is the presence of patchy consolidation in an initial radiograph (p = 0.025; OR 2.89; 95% CI 1.14-7.28).

CONCLUSIONS

The empirical anti-TB treatment in patients with sputum smear-negative presumptive pulmonary TB was effective and adequate, especially presented with patchy consolidation in initial chest radiographs in Korea.

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.

Assessment by meta-analysis of PCR for diagnosis of smear-negative pulmonary tuberculosis

We conducted a meta-analysis to assess the performance of PCR for the diagnosis of smear-negative pulmonary tuberculosis (SPT) and to identify factors that account for differences in the diagnostic accuracy of different studies. Studies published before February 2002 were included if sensitivity and specificity of PCR in smear-negative respiratory or gastric-aspirate specimens could be calculated. Analysis was conducted by using summary receiver operating characteristics models. Sensitivity and specificity ranged from 9 to 100% and from 25 to 100%, respectively. Fewer than 40% of the 50 studies reported results by number of patients, reported clinical characteristics of patients, or used as a reference standard combined culture and clinical criteria. Studies that included bronchial specimens showed higher accuracy than studies that evaluated only sputum specimens or included gastric aspirates. Studies that did not report that tests were applied blindly showed higher accuracy than those reporting blind testing. Increased sensitivity due to the use of DNA purification methods was associated with decreased specificity. Studies published after 1995, using Amplicor or dUTP-UNG, were associated with an increase in specificity at the expense of lower sensitivity. We concluded that PCR is not consistently accurate enough to be routinely recommended for the diagnosis of SPT. However, PCR of bronchial specimens could be useful in highly suspicious SPT cases. Studies not reporting blind testing are likely to overestimate accuracy of PCR. Future evaluation of PCR accuracy should be conducted by patient and type of respiratory specimen, blindly, by using a reference standard that combines culture and clinical criteria and addresses the issue of how patient characteristics affect PCR accuracy.

Clinical evaluation of Amplicor Mycobacterium detection system for the diagnosis of pulmonary mycobacterial infection using sputum

SETTING

The Amplicor Mycobacterium detection kit was evaluated for the diagnosis of active pulmonary mycobacterial infection using sputum.

OBJECTIVE

To assess the clinical usefulness of the Amplicor Mycobacterium kit for the diagnosis of pulmonary tuberculosis and non-tuberculous mycobacterial infection in the country of medium prevalence.

DESIGN

All the patients were diagnosed with bacterial, histopathological, and clinical 'gold standard'. The sensitivity and specificity for diagnosing clinically active pulmonary tuberculosis and Mycobacterium avium and Mycobacterium intracellulare infections were evaluated comparing Amplicor results and clinical diagnosis.

RESULTS

A total of 1088 sputum specimens were collected from 780 in and out patients. Mycobacteria were recovered from 339 specimens by culture. The sensitivity and specificity of conventional culture method for the diagnosis of pulmonary tuberculosis were 60.2% and 99.8% respectively based on the number of patients. The figures for Amplicor were 61.8% and 97.4% respectively. There was no statistical significant difference between these methods. In rapidity, the Amplicor was significantly superior to the microscopy method in sensitivity.

CONCLUSION

Patients with Amplicor positive and conventional negative result had mostly mycobacteria related diseases. The Amplicor positive result indicated mostly active mycobacterial infection and was clinically useful for rapid diagnosis.

Identifying pulmonary tuberculosis in patients with negative sputum smear results

BACKGROUND

Clinicians need to decide whether to begin empiric therapy for patients who are suspected of having tuberculosis (TB) but have negative sputum smear results. Culture results may take weeks, and delaying treatment may allow further transmission of disease.

STUDY OBJECTIVE

To identify the clinical, demographic, and radiographic characteristics that identify smear-negative patients who have TB, and to create a TB prediction rule.

DESIGN

Retrospective chart review.

SETTING

University-affiliated public hospital in San Francisco, CA, between 1993 and 1998.

PATIENTS

Forty-seven patients with TB and 141 control patients who were hospitalized with a suspicion of pulmonary TB; all had negative sputum smear results.

MEASUREMENTS AND RESULTS

Demographic, clinical, and radiographic variables were determined by chart review. In multivariate analysis, a positive tuberculin skin test result (odds ratio [OR], 4.8; 95% confidence interval [CI], 2.0 to 11.9) was independently associated with an increased risk of a positive TB culture finding. A radiographic pattern not typical of pulmonary tuberculosis (OR, 0.3; 95% CI, 0.1 to 0.7) and expectoration with cough (OR, 0.3; 95% CI, 0.1 to 0.6) were predictive of a decreased risk. An interaction between HIV seropositivity and mediastinal lymphadenopathy on the chest radiograph was also associated with a positive TB culture result (OR, 7.2; 95% CI, 1.4 to 36.0). The TB prediction score (TPS) was created with widely ranging likelihood ratios that could affect the posterior probability of TB by 30-fold.

CONCLUSION

The TPS put into context with the overall prevalence of TB in a given area may help clinicians decide if a patient with negative sputum smear results should start empiric antituberculous therapy or wait for culture results. These results need prospective validation.

Molecular Detection of Mycobacterium tuberculosis: Impact on Patient Care

Background: Nucleic acid amplification technologies such as PCR are revolutionizing the detection of infectious pathogens such as tuberculosis (TB). Amplification technology offers the potential for the diagnosis of TB in a few hours with a high degree of sensitivity and specificity. However, molecular assays neither replace nor reduce the need for conventional smear and culture, speciation, and antibiotic sensitivity assays.

Methods: We undertook prospective studies of sputum samples to assess the performance of two PCR-based assays for the detection of TB as well as the impact of more rapid availability of test results on patient care.

Results: The sensitivity of both the in-house and Amplicor PCR assays was 100% for smear-positive sputa. For smear-negative sputa (two sputum samples collected during the first 24 h of hospitalization), the sensitivity was 85% for our in-house PCR assay and 74% for the Roche PCR assay. Approximately 10% of the smear- and culture-negative sputa yielded positive PCR results; however, more than one-half of these were positive with both the in-house and Amplicor assays, suggesting the presence of TB DNA or organisms. Several of these came from patients whose other samples grew Mycobacterium tuberculosis during the same admission, and others came from patients who had previously treated TB. Overall, the specificities of the in-house and Amplicor PCR assays in smear-negative patients were 86% and 93%, respectively.

Conclusions: Molecular detection of slow-growing pathogens such as M. tuberculosis have the potential to improve clinical care through a dramatic reduction in the time required for detection and may provide substantial savings in the overall cost of care of a patient compared with conventional smear, culture, and speciation alone, despite the fact that conventional assays must still be performed for speciation of nontuberculous mycobacteria and for full assessment of antibiotic sensitivity.

Accuracy and utility of commercially available amplification and serologic tests for the diagnosis of minimal pulmonary tuberculosis

Diagnosis of patients with minimal active tuberculosis (TB) is difficult, as there is no single test with high sensitivity and specificity. The yield and clinical utility of a combination of diagnostic tests were prospectively studied among 500 consecutive patients referred for sputum induction for diagnosis of possible active TB. Patients underwent sputum induction, chest X-ray, tuberculin testing, and had blood drawn for serologic testing (Detect-TB test; Biochem ImmunoSystems). Sputum was examined with fluorescent microscopy and PCR (Amplicor MTB-Roche) and cultured for mycobacteria using liquid (BACTEC) and solid media. For the diagnosis of the 60 cases of active TB, sensitivity and specificity, respectively, of the following diagnostic tests were mycobacterial culture, 73% and 100%; PCR, 42% and 100%; chest X-ray, 67-77% and 66-76%; tuberculin testing, 94% and 20%; and serology, 33% and 87%. After consideration of PCR and radiographic and clinical characteristics, a positive serologic test was independantly associated with diagnosis of active disease (adjusted odds of disease if positive, 2.6; 95% confidence limits, 1.1,6.1). No currently available test has sensitivity and specificity high enough for the accurate diagnosis of minimal pulmonary TB. Utilization of a combination of tests, together with consideration of key clinical characteristics, could improve diagnostic accuracy.

Ligase chain reaction assay is clinically useful in the discrimination of smear-positive pulmonary tuberculosis from atypical mycobacterioses

We evaluated the usefulness of the ligase chain reaction (LCR) (Abbott LCx Mycobacterium tuberculosis assay) during the initial diagnosis of tuberculosis. LCx was carried out in parallel with conventional methods for the analysis of clinical samples. Out of 86 patients who were examined clinically, 53 were suspected of having pulmonary tuberculosis, eight had residual X-ray scars from previous tuberculosis and 25 served as asymptomatic controls. Ten bronchoscopy samples and 237 sputum samples were analysed by direct microscopy, culture and LCx. All 11 smear-positive and two of three smear-negative tuberculosis patients had at least one LCx-positive specimen. All samples that were both LCx- and smear-positive were culture-positive for M. tuberculosis. The smear-positive samples from the five patients with atypical mycobacteriosis were LCx-negative. There were three false-positive results: one in a smear-negative sample from a patient with M. malmoense infection and two from two pneumonia patients. All samples from controls and patients with previous tuberculosis were LCx-negative. The sensitivity, specificity and the positive and negative predictive values of LCx in patient analysis were 92.9%, 95.8%, 81.3% and 98.6%, respectively. LCx assay of M. tuberculosis is useful in rapid confirmation of tuberculosis or atypical mycobacteriosis from a smear-positive sample and may aid in diagnosing smear-negative tuberculosis.

Sensitive identification of mycobacterial species using PCR-RFLP on bronchial washings

In 98 patients (24 with active pulmonary tuberculosis [TB] lesions, 28 with cured TB lesions, and 46 with nontuberculous opacities [control group] in chest CT scans), we examined whether washing the bronchus after brushing the lesion, then applying polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) to the bronchial washings might be useful for diagnosing TB and nontuberculous mycobacteriosis (NTMosis). After biopsy and brushing with a bronchoscope, the bronchus connecting to the lesion was washed with 20 ml saline. The saline used for washing the brushes (5 ml; brushing sample), and 3 to 10 ml saline aspirated through the forceps channel (washing sample) were examined by PCR-RFLP, which proved able to identify Mycobacterium tuberculosis and seven species of nontuberculous mycobacteria (NTM). The values obtained for the sensitivity of the PCR-RFLP with respect to the brushing sample, the washing sample, and both samples mixed together were 70, 76, and 91%, respectively, when only patients who were culture-positive or radiologically improved after antituberculous therapy were considered as showing true infection. A mixture of brushing and washing samples provides useful material for PCR and culture, and the PCR-RFLP used here is a good method for the simultaneous identification of several species of mycobacterium (including M. tuberculosis).

Molecular techniques for the diagnosis of respiratory bacterial infection

DNA amplification techniques are now available for all of the major respiratory bacterial pathogens. The most important recent developments have been in the application of these techniques to routine clinical practice. A major problem for rapid techniques is the need to provide susceptibility results. Effective susceptibility techniques have now been described for Streptococcus pneumoniae and Mycobacterium tuberculosis. It has also been possible to use amplification techniques to monitor the response to antituberculosis chemotherapy by monitoring mRNA in sputum samples. The added sensitivity the amplification-based techniques give over conventional culture techniques is valuable not only in enhancing diagnosis, which allows the use of less invasive specimens, but also in opening new investigative areas in the pathogenesis of respiratory conditions.