Evaluation of the semiautomated Abbott LCx Mycobacterium tuberculosis assay for direct detection of Mycobacterium tuberculosis in respiratory specimens

Advances in the molecular diagnosis of tuberculosis: From probes to genomes

Tuberculosis, disease caused by Mycobacterium tuberculosis, is currently the leading cause of death by a single infectious agent worldwide. Early, rapid and accurate identification of M. tuberculosis and the determination of drug susceptibility is essential for the treatment and management of this disease. Tuberculosis diagnosis is mainly based on chest radiography, smear microscopy and bacteriological culture. Smear microscopy has variable sensitivity, mainly in patients co-infected with the human immunodeficiency virus (HIV). Conventional culture for M. tuberculosis isolation, identification and drug susceptibility testing requires several weeks owning to the slow growth of M. tuberculosis. The delay in the time to results drives the prolongation of potentially inappropriate antituberculosis therapy contributing to the emergence of drug resistance, reducing treatment options and increasing treatment duration and associated costs, resulting in increased mortality and morbidity. For these reasons, novel diagnostic methods are need for timely identification of M. tuberculosis and determination of the antibiotic susceptibility profile of the infecting strain. Molecular methods offer enhanced sensitivity and specificity, early detection and the capacity to detect mixed infections. These technologies have improved turnaround time, cost effectiveness and are amenable for point-of-care testing. However, although these methods produce results within hours from sample collection, the phenotypic susceptibility testing is still needed for the determination of drug susceptibility and quantify the susceptibility levels of a given strain towards individual antibiotics. This review presents the history, advances and forthcoming promises in the molecular diagnosis of tuberculosis. An overview on the general principles, diagnostic value and the main advantages and disadvantages of the molecular methods used for the detection and identification of M. tuberculosis and its associated disease, is provided. It will be also discussed how the current phenotypic methods should be used in combination with the genotypic methods for rapid antituberculosis susceptibility testing.

Use of amplified Mycobacterium tuberculosis direct test (Gen-probe Inc., San Diego, CA, USA) in the diagnosis of tubercular synovitis and early arthritis of knee joint

BACKGROUND

The diagnosis of knee joint tuberculosis, especially in early stages of synovial disease, has more often been based on clinicoradiological suspicion, with no single test claiming to be a dependable rapid diagnostic test with high sensitivity and specificity. Nuclear amplification tests in vogue like the polymerase chain reaction have shown variable sensitivity and false positivity rates in various studies. We evaluated the role of Amplified Mycobacterium tuberculosis Direct Test (AMTDT) or Genprobe in the diagnosis of knee joint tuberculosis in early, especially, early synovitis and arthritis cases.

PATIENTS AND METHODS

Thirty two patients of suspected knee joint tuberculosis were subjected to diagnostic arthroscopy during the study period. The synovial fluid and tissue were subjected to mycobacterial culture, histopathology, and AMTDT. A comparative analysis of the sensitivity and specificity of this new test with culture and histopathology was done and the time taken for reporting was calculated for each test.

RESULTS

Out of 32 tissue samples, 8 were found to be positive with mycobacterial culture [Lowenstein Jensen (LJ)/Bactec], 11 were positive with histopathology, and 5 were found to positive with AMTDT. The sensitivity of AMTDT was found to be 62.5% and specificity was 100% with a P value of 0.083. The results were obtained earliest with AMTDT with a mean reporting time of 1.2 days, while the results of histopathology were obtained in a mean time of 6.8 days, BacT alert in 22.5 days, and conventional LJ medium culture results in 48.6 days.

CONCLUSION

AMTDT or Genprobe is a rapid diagnostic test for early diagnosis of tubercular arthritis, but has low sensitivity in knee joint tuberculosis. Nuclear amplification tests are still far from being a single promising alternative to conventional tests in cases of joint tuberculosis. Routine use of arthroscopic biopsies in all suspected cases is helpful in the early diagnosis of knee joint tuberculosis.

Advances in rapid diagnosis of tuberculosis disease and anti-tuberculous drug resistance

Rapid diagnosis of tuberculosis (TB) and multidrug-resistant (resistance to at least rifampin and isoniazid) Mycobacterium tuberculosis (MDR-TB) is one of the cornerstones for global TB control as it allows early epidemiological and therapeutic interventions. The slow growth of the tubercle bacillus is the greatest obstacle to rapid diagnosis of the disease. However, considerable progress has recently been made in developing novel diagnostic tools, especially molecular methods (commercial and 'in-house'), for direct detection in clinical specimens. These methods, based on nucleic acid amplification (NAA) of different targets, aim to identify the M. tuberculosis complex and detect the specific chromosome mutations that are most frequently associated with phenotypic resistance to multiple drugs. In general, commercial methods are recommended since they have a better level of standardization, reproducibility and automation. Although some aspects such as cost-efficiency and the appropriate setting for the implementation of these techniques are not yet well established, organizations such as the WHO are strongly supporting the implementation and universal use of these new molecular methods. This chapter summarizes current knowledge and the available molecular methods for rapid diagnosis of TB and anti-tuberculous drug resistance in clinical microbiology laboratories.

[Utility of molecular biology in the microbiological diagnosis of mycobacterial infections]

Species within the Mycobacterium genus are of major medical interest, since, together with environmental and opportunistic species, there are two species (Mycobacterium tuberculosis and Mycobacterium leprae) that remain an important public health challenge. Despite efforts to control tuberculosis (TB), this disease remains one of the most prominent health problems worldwide. In the last few years, mycobacteriology has experienced major technological advances. Nevertheless, the early diagnosis of mycobacterial infection and, especially of TB, is still based on microscopic examination of properly stained samples. At present, this procedure is still the simplest, fastest and most cost-effective method for preliminary diagnostic guidance. Effective control of TB is based on rapid detection of M. tuberculosis, followed by immediate implementation of the appropriate antituberculosis therapy. Because of the emergence of multidrug resistant strains, the development of rapid diagnostic methods, both for identification of M. tuberculosis and susceptibility testing, has become a pressing need. The availability of molecular epidemiology methods that are easy to implement and standardized and that would allow identification of related cases is of key importance to identify epidemic outbreaks and control the spread of TB. Despite the evident progress in the molecular diagnosis of mycobacterial infections, the available techniques are still inadequate. In this review, we describe the state of the art of the main molecular techniques for direct detection of mycobacteria in clinical samples, their identification, detection of resistance to the most important antituberculosis agents, and molecular epidemiology. In each case, we describe the advantages and limitations of current techniques. In the near future, clinical mycobacteriology will probably evolve to the universal use of genetic techniques for direct diagnosis and detection of resistance. The molecular epidemiology of TB will be performed, in its various applications, by faster and more automated techniques than those currently available.

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.

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.

Tuberculous orchiepididymitis diagnosed by nucleic acid amplification test: a case report

Symptoms of tuberculous orchiepididymitis in a 39-year-old male started with swelling of left scrotum, followed by fistula formation with suppurative discharge. There was no any improvement produced by antibiotics. Surgical extirpation of inflammatory destroyed testicle and epidydimis was performed. Presence of tubercle bacilli was not shown by bacteriological analysis of testicle tissue. Tuberculous etiology was suggested after histopathological examination of testis and epididymis. Exudate from surgical wound was examined on presence of Mycobacterium tuberculosis DNA. Etiology of orchiepididymitis was proved by positive assay and inflammatory process was completely cured by antituberculotics therapy. By this report it was clearly shown that sometimes only molecular methods could confirm etiology of inflammatory process.

Emerging Homogeneous DNA-based Technologies in the Clinical Laboratory

Background: Advances in molecular diagnostic technologies have enabled genetic testing in single closed-tube reactions. The purpose of this review is to highlight some of the platforms and technologies currently available for the homogeneous detection of targets and the application of the technologies in the clinical setting. Validation issues surrounding the technologies, which may need to be addressed before they can become widely accepted, will also be discussed.

Approach: This review discusses the principles of several of the major technologies available for performing homogeneous genetic analyses. Publications arising from the application of the technologies in a wide range of clinical areas are used to highlight and compare the potential advantages and shortcomings of the various technologies.

Content: This review is descriptive and focuses on three areas: the technologies available for performing homogeneous analysis, the clinical applications where the technologies are being used, and validation issues surrounding the acceptance of the technologies in the general clinical setting.

Summary: This review intends to give the reader a greater understanding of the various technologies available for performing homogeneous genetic testing in the clinical laboratory. Through insight into the principles and performance characteristics underlying these technologies, the end user can evaluate their value and limitations in the clinical diagnostic setting.

Is the detection of Mycobacterium tuberculosis DNA by ligase chain reaction worth the cost: experiences from an inner London teaching hospital

AIMS

To evaluate the clinical usefulness and the costs of using a rapid, commercial ligase chain reaction test (LCx) to detect Mycobacterium tuberculosis directly from clinical samples.

METHODS

A prospective study of 2120 routine clinical specimens from 1161 patients over a 13 month period. Investigations for mycobacterial disease by microscopy, culture, and the Abbott LCx assay were performed. Sequential LCx assays were monitored in a cohort of patients undergoing treatment. The costs of the assay were calculated using the WELCAN system. Sensitivity, specificity, and positive and negative predictive values of the LCx assay were compared with conventional tests. The performance of the assay in patients undergoing treatment and cost in terms of WELCAN units converted to pounds/annum was studied.

RESULTS

The assay was 85%/88% sensitive and 98%/100% specific in culture confirmed/clinically confirmed cases of tuberculosis, respectively. The assay was not useful for the measurement of treatment outcomes. The test cost approximately 42,500 Pounds/annum.

CONCLUSIONS

The assay is a rapid, sensitive, and specific adjunct to clinical diagnosis, especially in differentiating non-tuberculous mycobacteria. However, it does not differentiate old and treated tuberculosis from reactivated disease, it is not useful to monitor adherence to treatment, and it is expensive.

The ligase chain reaction as a primary screening tool for the detection of culture positive tuberculosis

BACKGROUND

The ligase chain reaction Mycobacterium tuberculosis assay uses ligase chain reaction technology to detect tuberculous DNA sequences in clinical specimens. A study was undertaken to determine its sensitivity and specificity as a primary screening tool for the detection of culture positive tuberculosis.

METHODS

The study was conducted on 2420 clinical specimens (sputum, bronchoalveolar lavage fluid, pleural fluid, urine) submitted for primary screening for Mycobacterium tuberculosis to a regional medical microbiology laboratory. Specimens were tested in parallel with smear, ligase chain reaction, and culture.

RESULTS

Thirty nine patients had specimens testing positive by the ligase chain reaction assay. Thirty two patients had newly diagnosed tuberculosis, one had a tuberculosis relapse, three had tuberculosis (on antituberculous therapy when tested), and three had healed tuberculosis. In the newly diagnosed group specimens were smear positive in 21 cases (66%), ligase chain reaction positive in 30 cases (94%), and culture positive in 32 cases (100%). Using a positive culture to diagnose active tuberculosis, the ligase chain reaction assay had a sensitivity of 93.9%, a specificity of 99.8%, a positive predictive value of 83.8%, and a negative predictive value of 99.9%.

CONCLUSIONS

This study is the largest clinical trial to date to report the efficacy of the ligase chain reaction as a primary screening tool to detect Mycobacterium tuberculosis infection. The authors conclude that ligase chain reaction is a useful primary screening test for tuberculosis, offering speed and discrimination in the early stages of diagnosis and complementing traditional smear and culture techniques.

Detection of mycobacterium tuberculosis in paraffin-embedded pleural biopsy specimens by commercial ribosomal RNA and DNA amplification kits

STUDY OBJECTIVES

To evaluate the utility of two gene amplification systems in historical paraffin-embedded pleural biopsy (PEB) tissues from patients with pleural tuberculosis, and to compare the results to those obtained with conventional histologic and microbiological methods.

DESIGN

A retrospective study.

PATIENTS AND METHODS

Seventy-four formalin-fixed PEB tissues collected and stored over 12 years (1984 through 1995) were retrieved. Gene amplifications were performed in 57 tissues from patients with diagnoses of pleural tuberculosis and in 17 from patients with carcinoma as controls, using the first version of the Amplified Mycobacterium tuberculosis Direct Test (AMTDT; Gen-Probe; San Diego, CA) and the LCx Mycobacterium tuberculosis Assay (LCxMTB; Abbott Laboratories; Abbott Park, IL).

RESULTS

The sensitivities of the AMTDT and LCxMTB were 52.6% and 63.2%, respectively (p = not statistically significant). The specificity of both tests was 100%. Twenty tissue samples (35.1%) were positive by both systems, and 10 tissues (17.5%) were positive only by the AMTDT, while 16 tissues (28.1%) were positive only by the LCxMTB. Both tests gave negative results for 11 specimens (19.3%). When both tests were used, a positive diagnosis was achieved in 80.7% of the samples. Diagnosis of 73.7% of patient conditions had previously been made by smear examination of pleural biopsy and sputum, pleural liquid, or biopsy culture. The overall diagnostic yield with both culture and amplification techniques was 96.5% (55 of 57 patients) for pleural tuberculosis, with amplification techniques adding 22.8% of the diagnoses.

CONCLUSIONS

Amplification techniques are useful in archival PEB tissues, providing additional diagnoses beyond culturing, although the sensitivity should be improved, possibly by standardizing protocols.

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.

Multicenter evaluation of the Abbott LCx Mycobacterium tuberculosis ligase chain reaction assay

Four Australian hospital laboratories evaluated the performance of the Abbott LCx Mycobacterium tuberculosis assay with 2,347 specimens (2,083 respiratory and 264 nonrespiratory specimens) obtained from 1, 411 patients. A total of 152 specimens (6.5%) were culture positive for Mycobacterium tuberculosis complex (MTBC); of these, 79 (52%) were smear positive. After resolution of discrepant data, the overall sensitivity, specificity, and positive and negative predictive values for the LCx assay were 69.7, 99.9, 99.1, and 97.7% respectively. For smear-positive respiratory specimens that were culture positive for MTBC, the values were 98.5, 100, 100, and 98.4%, respectively, while the values for smear-negative respiratory specimens were 41.5, 99.9, 96.4, and 98%, respectively. Relative operating characteristic curves were constructed to demonstrate the relationship between sensitivity and specificity for a range of possible cutoff values in the LCx assay. These graphs suggested that the assay sensitivity for respiratory samples could be increased from 70.2 to 78.6%, while the specificity would be reduced from 99.9 to 99.4% by inclusion of a grey zone (i.e., LCx assay values of between 0.2 and 0.99). An algorithm is presented for the handling of specimens with LCx assay values within this grey zone.

Line probe assay in the rapid detection of rifampin-resistant Mycobacterium tuberculosis directly from clinical specimens

The sensitivity of a PCR-based line probe assay (Inno-LiPA Rif. TB Assay; Innogenetics NV Zwijndrecht, Belgium) was studied by using nested-PCR technique. A total of 75 specimens, representing various body locations from 70 suspected tuberculosis patients were obtained. LiPA yielded 30 Mycobacterium tuberculosis complex positive results (sensitivity 58.8%, compared with final diagnoses) whereas culture for M. tuberculosis was positive in 18 specimens (sensitivity 35.3%). Genotypic rifampin resistance testing by LiPA showed that 7 specimens contained rpoB mutations associated with RMP resistance, and sequencing data of the rpoB gene and LiPA patterns agreed in 29 of 30 M. tuberculosis positive specimens (96.7%). This indicates reliable performance, which makes the test suitable for the rapid determination of resistance to rifampin directly in clinical samples. However, the best results are obtained if LiPA is combined with conventional staining and culture methods.

Evaluation of three commercial detection systems for Mycobacterium tuberculosis where clinical diagnosis is difficult

AIMS

To assess the performance of three commercially available Mycobacterium tuberculosis detection systems employing nucleic acid amplification, when applied directly to respiratory and non-respiratory specimens from patients where the diagnosis of tuberculosis is difficult using clinical and traditional bacteriological methods.

METHODS

42 respiratory and 21 non-respiratory specimens were concentrated, examined with auramine staining, and cultured on Lowenstein-Jensen slopes. These specimens were also assayed using the Amplicor Mycobacterium tuberculosis test (AM) (Roche Diagnostic Systems), the Amplified Mycobacterium tuberculosis direct test (AMD) (Gen-Probe), and the LCx Mycobacterium tuberculosis assay (LMA) (Abbott Laboratories).

RESULTS

All three amplification systems used in this study gave specificities of 100% when used on respiratory specimens. When used on non-respiratory specimens, AM and LMA gave specificities of 100% and AMD 75%. With respiratory specimens the AM, AMD, and LMA systems gave sensitivities of 75%, 65.2%, and 79.2%, respectively. With non-respiratory specimens the sensitivities were 50%, 66.7%, and 60%, while with smear negative, culture positive specimens they were 33.3%, 66.7%, and 55.6%. Positive predictive values of 100% were seen with all specimens except non-respiratory specimens assayed using AMD where the value was 66.7%.

CONCLUSIONS

The manufacturers of these systems recommend that they should only be used for the direct analysis of respiratory specimens, and the US Food and Drug Administration has approved them for use only with smear positive specimens. This study confirms that sensitivities are lower for non-respiratory and smear negative specimens, but positive predictive values are high. Provided they are interpreted with caution, positive results with these tests in respiratory and non-respiratory specimens are useful in tuberculous patients who are otherwise difficult to diagnose. Each amplification has advantages and disadvantages compared with the others.

Multicenter evaluation of two commercial amplification kits (Amplicor, Roche and LCx, Abbott) for direct detection of Mycobacterium tuberculosis in pulmonary and extrapulmonary specimens

Direct detection of Mycobacterium tuberculosis was performed in parallel with the Amplicor M. tuberculosis test (Roche Diagnostic System, USA) and the LCx M. tuberculosis (Abbott Diagnostic Division, USA) on 697 samples, collected from 481 patients, in three different Italian laboratories. Though both systems are licensed only for pulmonary specimens, 113 extrapulmonary specimens (represented mainly by pleural fluids, cerebrospinal fluids and urines) were included in the study. Amplification results were compared with acid-fast microscopy, culture, and identification of isolates. Final clinical diagnosis was used to resolve discrepant results. M. tuberculosis was detected in 105 specimens by both assays, whereas 561 were agreeing negatives; 21 and 6 of the remaining true-positive samples scored positive with LCx only and with Amplicor only, respectively. There were three false-positives with LCx and one false-positive with Amplicor. The diagnostic sensitivity of both methods was significantly better when only respiratory specimens were considered (78% versus 59% in nonrespiratory samples with Amplicor, and 88% versus 65% with LCx). Our data reveal a significantly better sensitivity of the LCx (p = 0.026) and a slight better specificity of the Amplicor assay. It is noteworthy that 16 of the 21 Amplicor-negative specimens in which LCx detected M. tuberculosis were culture negative, thus suggesting that the higher diagnostic sensitivity of the latter assay is attributable to its better analytical sensitivity. However, the majority of such samples originated from patients under antimicrobial treatment, which makes uncertain the clinical significance of such increased sensitivity. Considering true-positive for LCx and true-negative for Amplicor, the 16 culture-negative/LCx-positive/Amplicor-negative specimens resulted true-positives after the resolution of discrepancies, the final overall sensitivity and specificity values of the LCx assay were not significantly different from the ones of the Amplicor assay.

[Usefulness of a gene amplification technique (LCx MTB) in the diagnosis of tuberculosis: preliminary results with different sputum samples]

OBJECTIVE

To evaluate the use in non-sputum samples of a commercial molecular amplification kit (LCx MTB, Abbott Diagnostica) (LCx) for the diagnosis of tuberculosis.

MATERIAL AND METHOD

Ninety-nine non-sputum samples from the same number of patients (bronchoalveolar, pleural and ascitic fluid, fecal samples, blood cultures, biopsies from different sites, cerebrospinal fluid, urine and gastric juices) and 14 sputum samples (10 from patients clinically suspected of having tuberculosis and 4 from patients diagnosed of tuberculosis and undergoing appropriate treatment for at least one month). All samples were LCx processed according to the manufacturer's instructions. The reference diagnosis was obtained by the Löwestein-jensen method and when results were inconsistent, we took into account the degree of clinical suspicion, response to treatment and histology.

RESULTS

Seven of the 99 samples were positive by the LCx technique, and 6 of the 7 were also LJ positive; 1 could not be evaluated because of culture contamination. One LJ positive culture was LCx negative. Only one sample was positive by Ziehl-Neelsen (ZN) staining. Ninety-two samples were LCx negative, with 91 showing no growth at all. Sensitivity was 86% and specificity 98%. Atypical mycobacteria were detected in 4 cases, all of which were LCx negative.

CONCLUSIONS

Diagnosis of tuberculosis by applying the LCx system to various types of samples other than sputum is simple, rapid, sensitive and specific.

Evaluation of the Abbott LCx Mycobacterium tuberculosis assay for direct detection of Mycobacterium tuberculosis complex in human samples

Seven hundred thirty-seven clinical samples from 460 patients were processed for direct detection of Mycobacterium tuberculosis complex by a semiautomated ligase chain reaction commercial assay, the LCx Mycobacterium tuberculosis Assay (LCx assay) from Abbott Laboratories. Results were compared to those of direct microscopy and standard microbiological culture. Of 26 patients (5.7%) with a culture positive for M. tuberculosis, 22 (84.6%) were found positive by the LCx assay. The sensitivity of the LCx assay was 98% for smear-positive samples and 27% for smear-negative samples. With an overall culture positivity rate for M. tuberculosis of 8.3% (61 of 737 samples) and after resolution of discrepant results according to clinical data, the sensitivity, specificity, and positive and negative predictive values of the LCx assay were 78, 100, 95, and 98%, respectively, compared to 85, 100, 100, and 98%, respectively, for culture and 67, 99, 87, and 97%, respectively, for acid-fast staining. In conclusion, the LCx assay proved satisfactory and appears to be an easy-to-use 1-day test which must be used with standard culture methods but can considerably reduce diagnosis time versus culture. However, its clinical interest appears to be limited in our population with low mycobacterial prevalence because of its cost considering the small gain in sensitivity versus direct microscopy.

LCx: a diagnostic alternative for the early detection of Mycobacterium tuberculosis complex

This study aims to evaluate the performance of a new diagnostic method (LCx Tuberculosis Assay, Abbott Laboratories) based on Ligase Chain Reaction (LCR) technology, for the detection of Mycobacterium tuberculosis in respiratory and non-respiratory specimens and compare it with standard microbiological data and the clinical diagnosis of tuberculosis. Nine hundred specimens were collected from patients with a high suspicion of tuberculosis (740 respiratory samples and 160 non-respiratory specimens). The study was divided into two separate groups: samples washed and distilled water (207 samples) and unwashed samples that were directly resuspended in phosphate buffer (693 samples). The overall sensitivity, specificity, positive and negative predictive values of samples washed with distilled water after decontamination with SDS-NaOH were: 54%, 100%, 100%, and 94%, respectively. If these results were divided according to origin of specimens, the sensitivity, specificity, positive and negative predictive values in respiratory and non-respiratory samples were 54.5%, 100%, 100%, 94% and 50 100%, 100%, 93%, respectively. In contrast, for the non-washed samples, values were 85%, 95%, 80% and 98%, respectively. Respiratory and non-respiratory samples gave values of 84%, 96%, 77%, and 97.5% versus 89%, 99%, 94%, and 98%. The LCx M. tuberculosis assay is a novel, semi-automated assay and a rapid and highly specific technique for screening all forms of tuberculosis, including non-respiratory forms.

Comparative evaluation of the new gen-probe Mycobacterium tuberculosis amplified direct test and the semiautomated abbott LCx Mycobacterium tuberculosis assay for direct detection of Mycobacterium tuberculosis complex in respiratory and extrapulmonary specimens

Two commercial assays that detect Mycobacterium tuberculosis complex (MTB) in clinical specimens by rRNA target amplification (AMTDII) and ligase chain reaction (LCx) were evaluated. The tests were applied to 457 respiratory (n = 273) and extrapulmonary (n = 184) specimens collected from 357 patients. The results were compared with those of acid-fast staining and culture. The combination of culture and clinical diagnosis was considered to be the "gold standard." Seventy specimens were from patients with pulmonary tuberculosis and 28 specimens were from patients with extrapulmonary tuberculosis. After resolution of discrepant results, the overall sensitivities, specificities, and positive and negative predictive values for respiratory specimens were 92.8, 99.4, 98.5, and 97%, respectively, for AMTDII and 75.7, 98.8, 96.4, and 90.5%, respectively, for LCx. With extrapulmonary specimens, the overall sensitivities, specificities, and positive and negative predictive values were 78.6, 99.3, 95.6, and 96.2%, respectively, for AMTDII and 53.6, 99.3, 93.7, and 92.1%, respectively, for LCx. The level of agreement between AMTDII and LCx assay results was 78.2%. We conclude that although both nucleic acid amplification methods are rapid and specific for the detection of MTB in clinical specimens, AMTDII is significantly more sensitive than LCx with both respiratory (P = 0.005) and extrapulmonary (P = 0.048) specimens.

Clinical evaluation of the automated COBAS AMPLICOR MTB assay for testing respiratory and nonrespiratory specimens

We evaluated the COBAS AMPLICOR PCR system (Roche Diagnostics) for the routine detection of Mycobacterium tuberculosis complex (MTBC) in clinical specimens. Diagnostic culture, considered as the reference method, was performed with BACTEC, Löwenstein-Jensen, Stonebrink, and Kirchner media. Occasionally MB-Redox, ESP, or MGIT medium was also used. A total of 643 respiratory and 506 nonrespiratory specimens collected from 807 patients were investigated. Of the 95 culture-positive specimens, 80 were COBAS AMPLICOR MTB positive, and of the 1,054 culture-negative specimens, 1,044 were COBAS AMPLICOR MTB negative. After resolving discrepancies by review of the medical history, the overall sensitivity, specificity, and positive and negative predictive values for the COBAS AMPLICOR MTB assay, respectively, were 83.5, 98.8, 86.7, and 98.6% compared to those of diagnostic culture. In smear-positive specimens, the sensitivity of the COBAS AMPLICOR MTB assay was 96%, versus 48% for smear-negative specimens. No significant differences in the test performance between respiratory and nonrespiratory specimens were observed. The overall inhibition rate was less than 2%, excluding stool specimens. The clear advantages of the COBAS AMPLICOR PCR system are standardized procedures and reagents for specimen processing as well as an internal control for reliable monitoring of PCR inhibitors. By simplifying the work flow through a completely automated amplification and amplicon detection procedure, the COBAS AMPLICOR PCR system proved itself as a very useful component for routine diagnostic procedures.

Rapid diagnosis of pulmonary tuberculosis with the LCx Mycobacterium tuberculosis assay and comparison with conventional diagnostic techniques

The LCx MTB amplification assay is a nucleic acid amplification test intended for the direct detection of Mycobacterium tuberculosis complex in respiratory specimens. We evaluated its performance on 2,001 consecutive respiratory specimens; 78 were culture positive for M. tuberculosis. Sensitivity, specificity, and positive and negative predictive values of this assay for all specimens compared to culture results were 88.5, 97.7, 60.5, and 99.5%, respectively. When referred to resolved clinical diagnosis of active tuberculosis, these values improved to 90.2, 98.4, 72.8, and 99.5%, respectively.

Clinical utility of an amplification test based on ligase chain reaction in pulmonary tuberculosis

We evaluated the sensitivity and specificity of a new semiautomated direct amplification test (DAT), the LCx-MTB, for the diagnosis of pulmonary tuberculosis (TB) and assessed its positive predictive value by focusing on patients with high clinical and radiologic suspicion of pulmonary TB. Respiratory tract specimens from 32 consecutive patients with high suspicion of active pulmonary TB (case patients) and from 204 control patients were cultured for Mycobacterium tuberculosis and tested by LCx-MTB. Sensitivity and specificity of LCx-MTB when compared with culture was, respectively, 80 and 98%. Pulmonary TB was confirmed in the 32 case patients without knowledge of the LCx results: 18 patients were smear- and culture-positive for M. tuberculosis, and all gave at least one specimen that was LCx-positive. Eight patients were smear-negative culture-positive, and seven gave at least one LCx-positive specimen. LCx-MTB was negative in all the specimens obtained from six patients with smear- and culture-negative TB. A positive LCx-MTB result in a smear negative specimen was 100% predictive that at least one of the case patients' specimens would yield M. tuberculosis. As a consequence, knowledge of the LCx-MTB results at the time of specimen collection could have hastened the start of the antituberculosis therapy in three (21%) smear-negative case patients and could have avoided unnecessary invasive diagnostic procedures in four (29%). We conclude that the sensitivity of LCx-MTB in detecting M. tuberculosis DNA in respiratory tract specimens is similar to other DATs, that LCx-MTB is a reliable test for confirmation of TB in smear-positive patients and that LCx-MTB could be beneficial as a diagnostic step in smear-negative patients with a high suspicion of pulmonary TB.

Detection of GB virus C by the RT-PCR LCx system

The recent publication of representative genomic sequences of GBV-C has permitted the selection of PCR primers for detection of GBV-C in clinical samples by PCR techniques. Traditional amplification methodologies which couple reverse transcription polymerase chain reaction (RT-PCR) and Southern blot detection are slow, cumbersome, and can be technique dependent. This has hampered studies to determine the clinical significance of GBV-C. We report the selection of highly conserved PCR primers and a probe useful for semi-automated RT-PCR using the Abbott LCx system. This adaptation of the LCx system expands its capabilities to include the detection of RNA by RT-PCR, in addition to DNA detection by ligase chain reaction (LCR).

Evaluation of ligase chain reaction for direct detection of Mycobacterium tuberculosis in respiratory specimens

A new automated amplification method, Ligase Chain Reaction (LCx MTB), was evaluated for direct detection of Mycobacterium tuberculosis in respiratory specimens from 208 patients and its performance was compared with culture and direct smears. Out of 226 specimens, 28 LCx MTB and 15 cultures were found positive for M. tuberculosis. After resolution of clinical history, the sensitivity of LCx MTB and culture was respectively 89.3% and 53.6% with a specificity of 98.5% and 100%. However, samples coming from untreated patients presented similar results between culture and LCx MTB (sensitivity 75% and 83.3% for culture and LCx MTB).

Clinical evaluation of a commercial ligase-based gene amplification method for detection of Mycobacterium tuberculosis

The purpose of this study was to evaluate the clinical usefulness of a commercial ligase-based gene amplification method (LCx Mycobacterium tuberculosis test; Abbott Laboratories, USA) for detection of Mycobacterium tuberculosis. The tuberculosis infection rate among clinical samples was 10.6%. The sensitivity, specificity, and positive and negative predictive values were 23.5%, 100%, 100%, and 91.7%, respectively, with the fluorochrome auramine stain; 32.4%, 100%, 100%, and 92.6%, respectively, with culture; and 76.5%, 95.8%, 68.4% and 97.2%, respectively, with the gene amplification method. When only samples from patients without current or previous treatment were studied, the sensitivity was 36.4% with the auramine stain, 63.6% with culture, and 100% with the gene amplification assay. The mean treatment time for culture-negative and assay-negative samples was greater than that of culture-negative and assay-positive samples. The LCx Mycobacterium tuberculosis test is a sensitive method for detection and identification of Mycobacterium tuberculosis. It produces few false-positive results. However, as it can remain positive after the culture becomes negative, it is not recommended for evaluation of treatment efficiency.

Rapid diagnosis of extrapulmonary tuberculosis by ligase chain reaction amplification

A rapid amplification-based test for the diagnosis of extrapulmonary tuberculosis, the LCx Mycobacterium tuberculosis Assay from Abbott Laboratories, was evaluated. Results from the LCx M. tuberculosis Assay were compared with those from culture and the final clinical diagnosis for each patient. A total of 526 nonrespiratory specimens from 492 patients were tested. The specimens included urine; feces; lymph node exudates; pleural, cerebrospinal, articular, and ascitic fluids; tissue biopsies; gastric aspirates; purulent exudates; blood; and bone marrow aspirates. After combination of the culture results and the patient's clinical data, a total of 135 specimens were collected from 122 patients with a diagnosis of extrapulmonary tuberculosis. The sensitivity, specificity, and positive and negative predictive values for the LCx M. tuberculosis Assay were 77.7, 98.7, 95.2, and 93.1%, respectively; these values rose in resolved cases of TB to 78.5, 100, 100, and 93.1%, respectively. For 37 (27.4%) specimens from patients smear positive for the disease and 98 (72.6%) specimens from patients smear negative for the disease, the sensitivities of the LCx M. tuberculosis Assay were 100 and 71.1%, respectively. Statistically significant differences (P < 0.01) in sensitivities were found between culture and the LCx M. tuberculosis Assay. These differences were even greater among smear-negative specimens. The results demonstrate that the LCx M. tuberculosis Assay will provide rapid and valuable information for the diagnosis of extrapulmonary tuberculosis.

Detection and identification of Mycobacterium tuberculosis directly from sputum sediments by ligase chain reaction

Sputum specimens received for the diagnosis of tuberculosis or other mycobacterial infections were tested by a ligase chain reaction (LCR)-based assay and acid-fast stain and culture techniques. Results from the LCR assay (Abbott LCx Mycobacterium tuberculosis [MTB] Assay) were compared to results from standard culture techniques held for 6 weeks. Four hundred ninety-three specimens from 205 patients suspected of pulmonary tuberculosis were included in the prospective study. Thirty-four (6.9%) of the specimens were culture positive for M. tuberculosis, and 13 (38%) of these were also fluorochrome stain positive. LCR sensitivities and specificities compared to culture were 74 and 98%, respectively. LCR sensitivity was 100% for fluorochrome stain-positive specimens and 57% for fluorochrome stain-negative specimens. Nine LCR-negative, culture-positive specimens were the result of low concentrations of M. tuberculosis. No inhibitors were detected in any of these specimens. Of the eight LCR-positive, culture-negative specimens, five were from patients with active tuberculosis. With these considered culture misses, final LCR sensitivity, specificity, positive predictive value, and negative predictive value were 77, 99, 91, and 98%, respectively. The same performance values for the fluorochrome acid-fast bacillus smear were 33, 98, 62, and 94%, respectively. After normal laboratory sputum processing, the Abbott LCx MTB Assay can be completed in 6 h. Thus, it is possible to have results available within 8 h of specimen submission.

Direct detection of Mycobacterium tuberculosis complex in clinical samples from patients in Norway by ligase chain reaction

Our aim was to investigate the use of DNA amplification with the ligase chain reaction (LCR) for detection of the Mycobacterium tuberculosis complex directly in human clinical specimens. The LCR assay employed was the Abbott LCx MTB Assay, which uses the gene encoding protein antigen b as the target template. Four hundred eighty-two samples from 457 patients in one clinical microbiology laboratory in Norway were processed by routine culture analysis (BACTEC culture), direct microscopy (Ziehl-Neelsen staining) and LCR. Of the 118 specimens containing cultivable M. tuberculosis, 106 (90.6%) were detected by LCR. Among the 364 culture-negative specimens, 356 samples were negative also by LCR and 8 (1.6%) were positive by LCR. In five of the eight LCR-positive and culture-negative samples, another sample from the same patient was M. tuberculosis culture positive and/or the patient had symptoms of tuberculosis. In comparison with culture, the sensitivity of LCR was 96.7% for smear-positive samples and 72.0% for smear-negative samples, respectively. For all samples combined, the sensitivity, specificity, and positive and negative predictive values were 90.2, 99.2, 97.4, and 96.7%, respectively. Challenging the M. tuberculosis LCR test with DNAs and cultures from strains of Mycobacterium ulcerans and Mycobacterium marinum, which are the mycobacterial species most closely related to the M. tuberculosis complex, resulted in all-negative test results. The sensitivity, specificity, and positive and negative predictive values of BACTEC culture in comparison with the LCR test and clinical criteria were 95.9, 100, 100, and 98.6%, respectively. A certain prioritization of samples subjected to the LCR assay should be based on clinical indications and risks with regard to infection transmission and patient isolation policy. More automation and lower expenses are generally desired for nucleic acid amplification kits. However, this M. tuberculosis LCR assay represents a valuable tool in routine mycobacterial diagnostics.