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

Development of the novel gene chip and restriction fragment length polymorphism (RFLP) methods for rapid detection of Mycobacterium tuberculosis complex in broth culture

BACKGROUND

Tuberculosis (TB) is a major global public health issue. Prompt and accurate TB diagnosis is crucial for starting appropriate treatments and preventing the disease's spread. Current diagnostic techniques are either slow or expensive. This study aimed to create and evaluate a new, fast, highly reliable, and cost-effective TB detection method using a gene chip and Restriction Fragment Length Polymorphism (RFLP) analysis on Mycobacteria Growth Indicator Tubes (MGIT) specimens.

METHODS

We assessed the effectiveness of a novel gene chip and RFLP methods targeting the 16S rRNA gene of Mycobacterium tuberculosis in 2000 MGIT culture-positive specimens. RFLP analysis identified the AfeI restriction site within the M. tuberculosis complex (MTBC) genome. Discrepancies were investigated through extensive sequencing and Cobas TaqMan PCR analysis, along with reviewing patient profiles.

RESULTS

Both methods showed high efficacy in detecting MTBC in broth cultures, with the gene chip method achieving a sensitivity of 99.27 %, specificity of 98.35 %, and the RFLP method showing a sensitivity of 98.18 %, specificity of 99.31 %. False negatives in two isolates were due to a mutation in the AfeI site. Additionally, five cases showed MTBC presence when nontuberculous Mycobacterium species grew in cultures.

CONCLUSION

Our novel gene chip and RFLP methods are effective for rapid highly-reliable and cost-effective M. tuberculosis detection in MGIT specimens. Both gene chip and RFLP methods are suitable for resource-limited settings, offering an economical advantage. These methods have significant potential to improve clinical TB diagnosis.

Performance assessment of SD Bioline TB MPT64 assay for the diagnosis of Mycobacterium tuberculosis complex in Lagos, Nigeria

This study assessed the performance of SD Bioline MPT64 immunochromatographic test for the identification of Mycobacterium tuberculosis complex (MTBC) in Nigeria.A total of 157 mycobacterial isolates, comprising 120 (76.4%) MTBC (M. tuberculosis, 112; M. africanum, 5; M. bovis, 3) and 37 (23.6%) non-tuberculous mycobacteria (NTM) isolates from patients attending six DOTS centers in Lagos between June 2012 and July 2014 were analyzed. All the isolates were grown on Bactec MGIT960 liquid media and identified in parallel by the conventional method and MPT64 immunochromatographic test. Discrepant results were resolved using the line probe assay.The comorbid disease rates for HIV and type 2 diabetes were 20.9% and 8.2%, respectively. Compared to the conventional method, SD Bioline MPT64 identified 117 MTBC isolates correctly, producing a sensitivity of 97.5% (95% CI, 92.9-99.2) at a shorter growing median time of 11 days compared to 26 days by the conventional method. The three undetected MTBC were confirmed by the line probe assay to be M. tuberculosis strains. The test also identified all the NTM correctly producing a specificity of 100% (95% CI, 90.7-100).This study supports the integration of SD Bioline TB MPT64 antigen test into diagnostic workflow for rapid MTBC case identification in Nigeria.

MPT64 assays for the rapid detection of Mycobacterium tuberculosis

Background

Tuberculosis (TB) is a serious infectious disease caused by Mycobacterium tuberculosis (MTB). An estimated 1.7 billion people worldwide are infected with Mycobacterium tuberculosis (LTBI) during the incubation period without any obvious symptoms. Because of MTB’s high infection and mortality rates, there is an urgent need to develop a fast, portable, and sensitive diagnostic technology for its detection.

Methods

We included research from PubMed, Cochrane Library, Web of Science, and Embase and extracted the data. MetaDisc and STATA were used to build forest plots, Deek’s funnel plot, Fagan plot, and bivariate boxplot for analysis.

Results

Forty-six articles were analyzed, the results of which are as follows: sensitivity and specificity were 0.92 (0.91–0.93) and 0.95 (0.94–0.95) respectively. The NLR and PLR were 0.04 (95% CI 0.03–0.07) and 25.32 (95% CI 12.38–51.78) respectively. DOR was 639.60 (243.04–1683.18). The area under the SROC curve (AUC) was 0.99.

Conclusions

MPT64 exhibits good diagnostic efficiency for MTB. There is no obvious heterogeneity between the three commercial kits.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06022-w.

Molecular Diagnosis of Tuberculosis

Tuberculosis (TB) is one of the leading causes of adult death in the Asia-Pacific Region, including Indonesia. As an infectious disease caused by Mycobacterium tuberculosis (MTB), TB remains a major public health issue especially in developing nations due to the lack of adequate diagnostic testing facilities. Diagnosis of TB has entered an era of molecular detection that provides faster and more cost-effective methods to diagnose and confirm drug resistance in TB cases, meanwhile, diagnosis by conventional culture systems requires several weeks. New advances in the molecular detection of TB, including the faster and simpler nucleic acid amplification test (NAAT) and whole-genome sequencing (WGS), have resulted in a shorter time for diagnosis and, therefore, faster TB treatments. In this review, we explored the current findings on molecular diagnosis of TB and drug-resistant TB to see how this advancement could be integrated into public health systems in order to control TB.

Performance of the SD Bioline TB Ag MPT64 Rapid test for quick confirmation of Mycobacterium bovis isolates from animals

Mycobacterium (M.) bovis, a bacterium in the M. tuberculosis complex, is a causative agent of bovine tuberculosis, a contagious disease of animals. Mycobacterial culture is the gold standard for diagnosing bovine tuberculosis, but this technique is laborious and time-consuming. In the present study, performance of the SD Bioline TB Ag MPT4 Rapid test, an immunochromatographic assay, was evaluated using reference bacterial strains and M. bovis field isolates collected from animals. The SD MPT64 Rapid test produced positive results for 95.5% (63/66) of the M. bovis isolates from cattle and 97.9% (46/47) of the isolates from deer. Additionally, the test had a sensitivity of 96.5% (95% CI, 91.2-99.0), specificity of 100% (95% CI, 96.7-100.0), positive predictive value of 100% (95% CI, 96.7-100.0), and negative predictive value of 92.9% (95% CI, 82.7-98.0) for M. bovis isolates. In conclusion, the SD MPT64 Rapid test is simple to use and may be useful for quickly confirming the presence of M. bovis in animals.

Comparison of an in-house multiplex PCR with two commercial immuno-chromatographic tests for rapid identification and differentiation of MTB from NTM isolates

BACKGROUND

Species specific diagnosis of mycobacterial infection is crucial because treatment of infections caused by Mycobacterium tuberculosis (MTB) differs from that of non-tuberculous mycobacterial (NTM) species. The species identification used to be cumbersome and non-reproducible a decade ago.

OBJECTIVES

Recently, some commercial tests have been made available to differentiate the MTB and NTM growths in culture media. Sensitivity and specificity of these tests was evaluated.

MATERIALS AND METHODS

In this double blind study 572 clinical samples were cultured in an automated BACTEC-MGIT-960 system. A total of 147 (25.7%) samples were MGIT culture positive. These cultures were subjected to an in-house m-PCR (which amplifies hsp-65, esat-6 and ITS region for MAC), two commercial immune-chromatographic tests (ICTs) and phenotypic tests.

RESULTS

Of the 147 MGIT positive cultures, m-PCR was able to correctly identify MTB in 123 cultures and NTM in 24 which included 3 MAC isolates. m-PCR showed 100% agreement with two gold standard methods-the nitrate reductase assay and PNB tests-in correctly identifying MTB. Commercial strips were able to correctly identify MTB in 120 (97.5%) of 123 cultures, while 3 (2.5%) isolates were falsely identified as NTM. However, none of the growth negative spent medium gave false positive results in any of the tests. None of the commercial strips misidentified any of the 24 NTM as MTB; hence, specificity of these strips was 100%. Of the 2 IC test systems, both SD Bioline and BD TBc strip tests missed 2.5% of MTB isolates and misidentified these as NTM.

CONCLUSION

The in-house m-PCR was found to be the most accurate and efficient tool for identifying the MTB, MAC and other NTMs.

Sensitivity, specificity, and reproducibility of the Capilia TB-Neo assay

The performance of the Capilia TB-Neo assay, a new-generation assay, was assessed by determining its sensitivity, specificity, reproducibility, and cross-reaction with contaminating organisms. The sensitivity and specificity were 99.2 and 96.4% and 89.3 and 100% in pure and mixed-culture isolates, respectively. The kappa statistic was 95.0 and 77.9% in pure and mixed culture isolates, respectively. There was no cross-reaction with contaminating organisms.

Evaluation of the Cobas TaqMan MTB real-time PCR assay for direct detection of Mycobacterium tuberculosis in respiratory specimens

The Cobas TaqMan MTB assay is a real-time PCR (qPCR) kit for rapid detection of Mycobacterium tuberculosis from clinical specimens. There are, however, limited studies validating its performance. We performed a prospective study in two hospitals in Taiwan on 586 respiratory specimens. By using culture as the reference method, the sensitivity and specificity of the Cobas TaqMan MTB assay were found to be 82.7 and 96.5 %, respectively. The sensitivity of the Cobas TaqMan MTB assay in acid-fast stain-negative respiratory specimens was only 34.9 %. Five specimens from five patients were positive for M. tuberculosis by the Cobas TaqMan MTB assay but were negative for M. tuberculosis by conventional culture methods. A diagnosis of pulmonary tuberculosis (TB) was made based on clinical and radiological findings as well as the response to anti-TB treatment in these five patients. Addition of data from these five specimens with discrepant results (PCR vs culture) from patients with symptoms clinically compatible with TB increased the sensitivity of the Cobas TaqMan MTB assay to 83.1 %. The Cobas TaqMan MTB assay is a rapid identification tool with a high degree of specificity for the direct detection of M. tuberculosis in respiratory specimens. The sensitivity for detecting acid-fast smear-negative respiratory specimens, however, is low.

Detonation nanodiamonds for rapid detection of clinical isolates of Mycobacterium tuberculosis complex in broth culture media

Routinely used molecular diagnostic methods for mycobacterium identification are expensive and time-consuming. To tackle this problem, we develop a method to streamline identification of Mycobacterium tuberculosis complex (MTBC) in broth culture media by using detonation nanodiamonds (DNDs) as a platform to effectively capture the antigen secreted by MTBC which is cultured in BACTEC MGIT 960, followed by the analysis of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS). The 5 nm DNDs can capture the MTBC secretory antigen without albumin interference. With on diamond digestion, we confirm the DND captured antigen is cell filtrate protein 10 (CFP-10) because its Mascot analysis shows a score of 68. The dot blotting method further verifies a positive reaction with anti-CFP-10, indicating that CFP-10 is secreted in the medium of mycobacterium growth indicator tube (MGIT) and captured by DNDs. The minimal CFP-10 protein detection limit was 0.09 μg/mL. Furthermore, our approach can avoid the false-positive identification of MTBC by immunological methods due to cross-reactivity. Five hundred consecutive clinical specimens subjected to routine mycobacteria identification in hospital were used in this study, and the sensitivity of our method is 100% and the specificity is 98%. The analysis of each MTBC sample from culture solution can be finished within 1 h and thus shortens the turnaround time of MTBC identification of gold standard culture methods. In sum, DND MALDI-TOF MS for the detection of MTBC is rapid, specific, safe, reliable, and inexpensive.

Use of immunochromatographic assay for rapid identification of Mycobacterium tuberculosis complex from liquid culture

A new, simple immunochromatographic assay for rapid identification of Mycobacterium tuberculosis complex in liquid cultures has been developed. The principle of the assay is binding of the Mycobacterium tuberculosis complex specific antigen to the monoclonal antibody conjugated on the test strip. The aim of this study is evaluation of the performance of immunochromatographic assay in identification of Mycobacterium tuberculosis complex in primary positive liquid cultures of BacT/Alert automated system. A total of 159 primary positive liquid cultures were tested using the immunochromatographic assay (BD MGIT TBc ID) and the conventional subculture, followed by identification using biochemical tests.Of 159 positive liquid cultures, using the conventional method, Mycobacterium tuberculosis was identified in 119 (74.8%), nontuberculous mycobacteria were found in 4 (2.5%), 14 (8.8%) cultures were contaminated and 22 (13.8%) cultures were found to be negative. Using the immunochromatographic assay, Mycobacterium tuberculosis complex was detected in 118 (74.2%) liquid cultures, and 41 (25.8%) tests were negative. Sensitivity, specificity, positive and negative predictive values of the test were 98.3%; 97.5%; 99.15% i 95.12%, respectively. The value of kappa test was 0.950, and McNemar test was 1.00. The immunochromatographic assay is a simple and rapid test which represents a suitable alternative to the conventional subculture method for the primary identification of Mycobacterium tuberculosis complex in liquid cultures of BacT/Alert automated system.

Relatively low primary drug resistant tuberculosis in southwestern Ethiopia

Background

The prevalence of drug resistant tuberculosis (TB) in Ethiopia in general, and Jimma area in particular, is not well documented. We conducted a study at Jimma University specialized hospital in southwest Ethiopia among new cases of smear positive TB patients to determine the pattern of resistance to first-line drugs.

Methods

A health institution based cross sectional study was conducted from November 2010 to September 2011. Any newly diagnosed smear positive TB patient 18 years and above was included in the study. Demographic and related data were collected by trained personnel using a pretested structured questionnaire. Mycobacterial drug susceptibility testing (DST) to the first line drugs isoniazid (INH), rifampicin (RIF), ethambutol (EMB) and streptomycin (STM) was performed on cultures using the indirect proportion method. M. tuberculosis complex (MTBC) was identified with the Capilia TB-Neo test.

Results

136 patients were enrolled in the study. Resistance to at least one drug was identified in 18.4%. The highest prevalence of resistance to any drug was identified against INH (13.2%) followed by STM (8.1%). There was no statistically significant difference in the proportion of any resistance by sex, age, HIV status and history of being imprisoned. The highest mono resistance was observed against INH (7.4%). Mono resistance to streptomycin was associated with HIV infection (crude OR 15.63, 95%CI: 1.31, 187). Multidrug-resistance TB (MDR-TB) was observed in two patients (1.5%).

Conclusion

Resistance to at least one drug was 18.4% (INH-13.2% and STM-8.1%). STM resistance was associated with HIV positivity. There was relatively low prevalence of MDR-TB yet INH resistance was common around Jimma. The capacity of laboratories for TB culture and DST should be strengthened, in order to correctly manage TB patients and avoid amplification of drug resistance.

Clinical research and development of tuberculosis diagnostics: moving from silos to synergy

The development, evaluation, and implementation of new and improved diagnostics have been identified as critical needs by human immunodeficiency virus (HIV) and tuberculosis researchers and clinicians alike. These needs exist in international and domestic settings and in adult and pediatric populations. Experts in tuberculosis and HIV care, researchers, healthcare providers, public health experts, and industry representatives, as well as representatives of pertinent US federal agencies (Centers for Disease Control and Prevention, Food and Drug Administration, National Institutes of Health, United States Agency for International Development) assembled at a workshop proposed by the Diagnostics Working Group of the Federal Tuberculosis Taskforce to review the state of tuberculosis diagnostics development in adult and pediatric populations.

Performance of the MGIT TBc identification test and meta-analysis of MPT64 assays for identification of the Mycobacterium tuberculosis complex in liquid culture

Rapid MPT64-based immunochromatographic tests (MPT64 ICTs) have been developed to detect Mycobacterium tuberculosis complex (MTBC) in culture. We demonstrated the noninferiority of one commercial MTP64 ICT, the MGIT TBc identification (TBcID) test, to GenoType line probe assays for MTBC identification in positive MGIT cultures. Meta-analysis of MPT64 ICT performance for identification of MTBC in liquid culture confirmed similar very high sensitivities and specificities for all three commercial MPT64 assays for which sufficient data were available.

Evaluation of the Bactec MGIT 960 system in combination with the MGIT TBc identification test for detection of Mycobacterium tuberculosis complex in respiratory specimens

The sensitivity and specificity of the MGIT TBc identification (TBc ID) test for Mycobacterium tuberculosis complex (MTC) detection in positive Bactec MGIT cultures were 95.2% and 99.2%, respectively. When MTC-positive results obtained from two additional molecular methods were included, the sensitivity of the MGIT TBc ID test was 85.4%, while that of culture was 95.7%.

Evaluation of TBc identification immunochromatographic assay for rapid identification of Mycobacterium tuberculosis complex in samples from broth cultures

Tuberculosis (TB) is a disease of major public health concern worldwide, especially in developing countries. In addition, the human immunodeficiency virus (HIV) epidemic has increased the incidence of infection with nontuberculous mycobacteria (NTM). Rapid, accurate, and simple methods for differentiation of Mycobacterium tuberculosis complex (MTBC) isolates from NTM is greatly needed for successful control of the TB epidemic. This study was done to evaluate the clinical performance of the BD MGIT TBc identification test (TBc ID) for rapid identification of MTBC in samples from broth cultures. A total of 229 Ziehl-Neelsen (ZN) stain-positive MGIT cultures were tested using the TBc ID test, and the results were compared with those of the AccuProbe MTBC identification test (GenProbe, San Diego, CA). The agreement between the TBc ID test and the AccuProbe assay was 96% (kappa = 0.92; confidence interval [CI] = 0.869 to 0.971). The sensitivity, specificity, and negative and positive predictive values of the TBc ID test compared to the AccuProbe assay were 100%, 92.4%, 100%, and 92.2%, respectively. After additional molecular testing, the agreement between the two methods increased to 97.8% (kappa = 0.96; CI = 0.917 to 0.994), and the specificity and positive predictive value increased to 95.6% and 95.7%, respectively. The TBc ID test is a simple, sensitive, and specific test for identification of MTBC in samples from acid-fast bacillus (AFB) smear-positive cultures. The TBc ID test could be a good alternative to the AccuProbe test in TB diagnostic laboratories.

Assessment of the SD Bioline Ag MPT64 Rapid™ and the MGIT™ TBc identification tests for the diagnosis of tuberculosis

Successful control of tuberculosis relies on the rapid detection of Mycobacterium tuberculosis. Few chromatographic lateral flow assays for the discrimination of the M. tuberculosis complex were developed from culture media. We compared the values of 2 assays to assess their place in diagnosis of tuberculosis. We conclude of their efficiency and relevance to supplant the conventional methods.

Evaluation of the rapid MGIT TBc identification test for culture confirmation of Mycobacterium tuberculosis complex strain detection

A culture confirmation test for the detection of Mycobacterium tuberculosis complex strains that uses a lateral-flow immunochromatographic assay to detect the MPB64 antigen, the MGIT TBc identification (TBc ID) test, has been developed. We evaluated the performance of the TBc ID test in the detection of the M. tuberculosis complex in 222 primary-positive liquid cultures. We compared these results to those of nucleic acid-based identification and conventional biochemical tests. The validity of the TBc ID test was determined, and all of the nontuberculous mycobacteria (NTM) and Nocardia species tested were found to be negative. The detection limit of the TBc ID test was 5 × 10(5) CFU/ml, and for IS6110 real-time PCR it was 5 CFU/ml. All of the M. tuberculosis and M. africanum cultures were found to be positive, while M. bovis and M. bovis BCG cultures were negative. With the exception of 1 contaminated culture, the 221 culture-positive isolates contained 171 (77.5%) M. tuberculosis isolates, 39 (17.6%) NTM species, and 11 (5.0%) unidentified species. Two culture-positive isolates harbored a 63-bp deletion at position 196 of the mpb64 gene. The sensitivity, specificity, positive predictive values, and negative predictive values of the TBc ID test were 98.8, 100, 100, and 95.1%, respectively. Furthermore, the approximate turnaround time for real-time PCR was 4 h (including buffer and sample preparation), while for the TBc ID test it was less than 1 h. We suggest an algorithm for the primary identification of M. tuberculosis in liquid culture using the TBc ID test as an alternative to conventional subculture followed by identification using biochemical methods.

Rapid identification of the Mycobacterium tuberculosis complex by combining the ESAT-6/CFP-10 immunochromatographic assay and smear morphology

Early secretory antigen 6 (ESAT-6) and cell filtrate protein 10 (CFP-10) are two antigens secreted as a complex by the replicating Mycobacterium tuberculosis complex (MTC). Recently, an immunochromatographic assay (ICA) using a monoclonal antibody against the ESAT-6/CFP-10 complex was developed for the purpose of MTC detection. In this study, the efficacy of the assay was tested with 603 BACTEC cultures that were incubated for 3 additional days after positive signals appeared in the BACTEC MGIT 960 system. Bacterial isolates were recovered from these 603 BACTEC cultures, and 332 MTC isolates, 270 nontuberculosis mycobacterial isolates, and 1 Nocardia isolate were identified by using standard biochemical assays. The ESAT-6/CFP-10 assay detected 322 MTC cultures, resulting in a sensitivity of 97% and a specificity of 97.4%. To reduce the false-negative rate and improve the sensitivity, either serpentine cording in an acid-fast bacillus stain of the cultural smear, the ESAT-6/CFP-10 assay, or a combination of both was used for MTC detection. The sensitivity was then increased to 99.1%, and the negative predictive value increased to 98.9%, but the specificity decreased to 94.8% and the positive predictive value decreased to 95.9%. However, a combination of serpentine cording in cultural smears and the positivity of the ICA resulted in the specificity and positive predictive values of 100%. Therefore, BACTEC cultures with both serpentine cording and positivity of the ESAT-6/CFP-10 assay could be reported to contain MTC directly. The ESAT-6/CFP-10 assay may be an alternative of the Capilia assay (MPB64-ICA) as a convenient and cost-effective method for identification of MTC in culture.

Evaluation of the Capilia TB assay for culture confirmation of Mycobacterium tuberculosis infections in Zambia and South Africa

The performance and cost of the Capilia TB assay were evaluated for use in a resource-limited setting. The sensitivity and specificity were 99.6% and 99.5%, respectively. The incremental costs of the Capilia test were estimated to be $1.46 and $1.84 when the test was added to liquid and solid culture processes, respectively. These findings suggest that the Capilia TB assay represents a rapid, simple, and inexpensive Mycobacterium tuberculosis identification test that can be used in resource-limited settings.

Submandibular lymphadenitis caused by Mycobacterium interjectum: contribution of new diagnostic tools

Mycobacterium interjectum is a rare causative agent of cervical lymphadenitis. We describe a 2-year-old girl with suspected tuberculous cervical lymphadenitis.Sequencing of the 16S rRNA gene allowed the correct identification of Mycobacterium interjectum. As yet, only nine case reports of infections due to M. interjectum in children have been reported in the literature, and in all of them a correct identification could only be obtained using gene sequencing.

Diagnostic performance of an enzyme-linked immunospot assay for interferon-gamma in extrapulmonary tuberculosis varies between different sites of disease

OBJECTIVES

To evaluate diagnostic performance of an enzyme-linked immunospot assay for interferon-gamma (T SPOT-TB) in patients with suspected extrapulmonary tuberculosis (TB).

METHODS

From January 2007 to December 2008, patients with suspected extrapulmonary TB were prospectively enrolled from 2 tertiary care hospitals.

RESULTS

A total of 138 patients with suspected extrapulmonary TB were enrolled; 50 patients had positive culture for Mycobacterium tuberculosis and 39 patients had probable TB. The sites of infection were lymph node (n = 20), pleura (n = 19), bone/joint (n = 15), urinary tract (n = 7), peritoneum (n = 7), meninges (n = 6), disseminated (n = 5), intestine (n = 3), pericardium (n = 2), skin (n = 2), throat (n = 1), neck (n = 1), and genitalia (n = 1). The overall sensitivity and specificity were 79.8% (71/89) and 81.6% (40/49). The sensitivity ranged from 100% for tuberculous meningitis, tuberculous pericarditis, and intestinal TB, 95% for lymphadenitis, to 42.9% for tuberculous peritonitis. The sensitivity of the T SPOT-TB assay was 70.6% in immunocompromised patients and 85.5% in immunocompetent patients (p = 0.09).

CONCLUSIONS

The T SPOT-TB assay can be a useful tool for diagnosing extra-pulmonary TB in immunocompetent and immunocompromised patients, particularly for tuberculous meningitis, pericarditis, lymphadenitis, and intestinal TB.

Isothermal DNA amplification in vitro: the helicase-dependent amplification system

Since the development of polymerase chain reaction, amplification of nucleic acids has emerged as an elemental tool for molecular biology, genomics, and biotechnology. Amplification methods often use temperature cycling to exponentially amplify nucleic acids; however, isothermal amplification methods have also been developed, which do not require heating the double-stranded nucleic acid to dissociate the synthesized products from templates. Among the several methods used for isothermal DNA amplification, the helicase-dependent amplification (HDA) is discussed in this review with an emphasis on the reconstituted DNA replication system. Since DNA helicase can unwind the double-stranded DNA without the need for heating, the HDA system provides a very useful tool to amplify DNA in vitro under isothermal conditions with a simplified reaction scheme. This review describes components and detailed aspects of current HDA systems using Escherichia coli UvrD helicase and T7 bacteriophage gp4 helicase with consideration of the processivity and efficiency of DNA amplification.

Impact and cost-effectiveness of culture for diagnosis of tuberculosis in HIV-infected Brazilian adults

Background

Culture of Mycobacterium tuberculosis currently represents the closest “gold standard” for diagnosis of tuberculosis (TB), but operational data are scant on the impact and cost-effectiveness of TB culture for human immunodeficiency (HIV-) infected individuals in resource-limited settings.

Methodology/Principal Findings

We recorded costs, laboratory results, and dates of initiating TB therapy in a centralized TB culture program for HIV-infected patients in Rio de Janeiro, Brazil, constructing a decision-analysis model to estimate the incremental cost-effectiveness of TB culture from the perspective of a public-sector TB control program. Of 217 TB suspects presenting between January 2006 and March 2008, 33 (15%) had culture-confirmed active tuberculosis; 23 (70%) were smear-negative. Among smear-negative, culture-positive patients, 6 (26%) began TB therapy before culture results were available, 11 (48%) began TB therapy after culture result availability, and 6 (26%) did not begin TB therapy within 180 days of presentation. The cost per negative culture was US$17.52 (solid media)–$23.50 (liquid media). Per 1,000 TB suspects and compared with smear alone, TB culture with solid media would avert an estimated eight TB deaths (95% simulation interval [SI]: 4, 15) and 37 disability-adjusted life years (DALYs) (95% SI: 13, 76), at a cost of $36 (95% SI: $25, $50) per TB suspect or $962 (95% SI: $469, $2642) per DALY averted. Replacing solid media with automated liquid culture would avert one further death (95% SI: −1, 4) and eight DALYs (95% SI: −4, 23) at $2751 per DALY (95% SI: $680, dominated). The cost-effectiveness of TB culture was more sensitive to characteristics of the existing TB diagnostic system than to the accuracy or cost of TB culture.

Conclusions/Significance

TB culture is potentially effective and cost-effective for HIV-positive patients in resource-constrained settings. Reliable transmission of culture results to patients and integration with existing systems are essential.