A comparative evaluation of dot immunobinding assay (Dot-Iba) and polymerase chain reaction (PCR) for the laboratory diagnosis of tuberculous meningitis

A Systematic Review and Meta-analysis of the Diagnostic Accuracy of Nucleic Acid Amplification Tests for Tuberculous Meningitis

The diagnosis of tuberculous meningitis (TBM) is difficult and poses a significant challenge to physicians worldwide. Recently, nucleic acid amplification (NAA) tests have shown promise for the diagnosis of TBM, although their performance has been variable. We undertook a systematic review and meta-analysis to evaluate the diagnostic accuracy of NAA tests with cerebrospinal fluid (CSF) samples against that of culture as the reference standard or a combined reference standard (CRS) for TBM. We searched the Embase, PubMed, Web of Science, and Cochrane Library databases for the relevant records. The QUADAS-2 tool was used to assess the quality of the studies. Diagnostic accuracy measures (i.e., sensitivity and specificity) were pooled with a random-effects model. All statistical analyses were performed with STATA (version 14 IC; Stata Corporation, College Station, TX, USA), Meta-DiSc (version 1.4 for Windows; Cochrane Colloquium, Barcelona, Spain), and RevMan (version 5.3; The Nordic Cochrane Centre, the Cochrane Collaboration, Copenhagen, Denmark) software. Sixty-three studies comprising 1,381 cases of confirmed TBM and 5,712 non-TBM controls were included in the final analysis. These 63 studies were divided into two groups comprising 71 data sets (43 in-house tests and 28 commercial tests) that used culture as the reference standard and 24 data sets (21 in-house tests and 3 commercial tests) that used a CRS. Studies which used a culture reference standard had better pooled summary estimates than studies which used CRS. The overall pooled estimates of sensitivity, specificity, positive likelihood ratio (PLR), and negative likelihood ratio (NLR) of the NAA tests against culture were 82% (95% confidence interval [CI], 75 to 87%), 99% (95% CI, 98 to 99%), 58.6 (95% CI, 35.3 to 97.3), and 0.19 (95% CI, 0.14 to 0.25), respectively. The pooled sensitivity, specificity, PLR, and NLR of NAA tests against CRS were 68% (95% CI, 41 to 87%), 98% (95% CI, 95 to 99%), 36.5 (95% CI, 15.6 to 85.3), and 0.32 (95% CI, 0.15 to 0.70), respectively. The analysis has demonstrated that the diagnostic accuracy of NAA tests is currently insufficient for them to replace culture as a lone diagnostic test. NAA tests may be used in combination with culture due to the advantage of time to result and in scenarios where culture tests are not feasible. Further work to improve NAA tests would benefit from the availability of standardized reference standards and improvements to the methodology.

Dot-immunobinding assay (Dot-Iba)

Dot-immunobinding assay (Dot-Iba) is a simple and highly reproducible immunodiagnostic method. Antibody or antigen is dotted directly onto nitrocellulose membrane (NCM) discs. The diagnostic material to be checked can be incubated on this disc. Presence of antigen-antibody complex in NCM discs can be directly demonstrated with enzyme-conjugated antiglobulins and substrate. Development of a purple-pink colored, insoluble substrate product in the nitrocellulose membrane will be considered a positive result in the assay. This assay allows the processing of multiple specimens at a time and the entire operational procedures required only 4-6 h. Dot-IBA is rapid and the technical steps involved in the assay are much simpler than the other immunoassays such as enzyme-linked immunosorbent assay in detecting circulating antigen and antibody in clinical samples. The Dot-Iba showed an overall sensitivity of 60 % for tuberculous meningitis diagnosis and no false positive results were encountered. Hence this assay is highly specific for the diagnosis of paucibacillary diseases like extrapulmonary tuberculosis. Dot-Iba is best suited to laboratories in developing world where there are constraints in laboratory resources.

Comparison of real time IS6110-PCR, microscopy, and culture for diagnosis of tuberculous meningitis in a cohort of adult patients in Indonesia

BACKGROUND

Bacteriological confirmation of tuberculous (TB) meningitis is difficult. Culture is slow and microscopy has insufficient sensitivity. We evaluated real time PCR targeting insertion sequence IS6110 among 230 consecutive adult patients with subacute meningitis in a referral hospital in Indonesia.

METHODS

Cerebrospinal fluid (CSF) samples were examined using microscopy, solid and liquid culture, and real time IS6110-PCR with a fluorescence-labeled probe using DNA extracted from CSF. CSF samples from 40 non-infectious neurology patients were used as negative controls. IS6110-PCR results were linked with clinical and CSF characteristics.

RESULTS

Most patients presented with subacute meningitis, after a median of 14 days of symptoms (range 7-30). After exclusion of cryptococcal and bacterial meningitis, 207 patients were classified as definite or probable TB meningitis; 17.9% with HIV infection. Among this group IS6110-PCR gave the highest positivity rate (68%, 95% CI 62-74%) compared with microscopy of ZN-stained slides (11%, 95% CI 7-15%), and mycobacterial culture using solid (36%, 95% CI 29-42%) and liquid (44%, 95% CI 37-51%) media. IS6110-PCR was positive in 92% of patients with culture-positive and 42% of patients with culture-negative probable TB meningitis. Among culture-negative patients, a positive PCR was associated with a history of TB treatment, a longer duration of illness, a higher CSF cell count and protein, and a lower CSF glucose. IS6110-PCR was negative in all CSF samples from non-meningitis control patients.

CONCLUSIONS

Real time IS6110-PCR is a quick, sensitive, and specific test for diagnosing of TB meningitis in this setting. Its performance in other (less-developed) settings needs further study.

Multiplex PCR for rapid diagnosis of tuberculous meningitis

Rapid and specific diagnosis of tubercular meningitis is of paramount importance to decrease morbidity and mortality. The aim of the study was to evaluate multiplex PCR using protein b, MPB 64, and IS6110 primers directed against M. tuberculosis complex for the diagnosis of tuberculous meningitis (TBM). Multiplex PCR was performed on 18 TBM confirmed cases (culture was positive), 92 clinically suspected TBM cases and 100 non-TBM (control group) patients. Multiplex PCR had a sensitivity of 94.4% for confirmed cases and specificity of 100% for confirmed TBM cases. In 92 clinically diagnosed but unconfirmed TBM cases, multiplex PCR was positive in 84.78% cases. The overall sensitivity of microscopy, culture and multiplex cases were 1.81, 16.73, and 86.63% and specificity was 100, 100, and 100% respectively. Multiplex PCR using protein b, MPB 64, and IS6110 primers has a high sensitivity and specificity in diagnosis of tubercular meningitis.

Dot-immunobinding assay

Dot-immunobinding assay (Dot-Iba) is a simple and highly reproducible immunodiagnostic method. Antibody or antigen is dotted directly onto nitrocellulose membrane (NCM) discs. The diagnostic material to be checked can be incubated on this disc. Presence of antigen-antibody complex in NCM discs can be directly demonstrated with enzyme-conjugated antiglobulins and substrate. Development of a purple-pink colored, insoluble substrate product in the NCM will be considered a positive result in the assay. This assay allows the processing of multiple specimens at a time and the entire operational procedures require only 4-6 h. Dot-Iba is rapid, and the technical steps involved in the assay are much simpler than in the other immunoassays such as enzyme-linked immunosorbant assay in detecting circulating antigen and antibody in clinical samples. The Dot-Iba showed an overall sensitivity of 60% for tuberculous meningitis diagnosis and no false positive results were encountered. Hence, this assay is highly specific for the diagnosis of paucibacillary diseases such as extrapulmonary tuberculosis. Dot-Iba is best suited to laboratories in developing world where there are constraints in laboratory resources.

Central nervous system tuberculosis: pathogenesis and clinical aspects

Tuberculosis of the central nervous system (CNS) is a highly devastating form of tuberculosis, which, even in the setting of appropriate antitubercular therapy, leads to unacceptable levels of morbidity and mortality. Despite the development of promising molecular diagnostic techniques, diagnosis of CNS tuberculosis relies largely on microbiological methods that are insensitive, and as such, CNS tuberculosis remains a formidable diagnostic challenge. Insights into the basic neuropathogenesis of Mycobacterium tuberculosis and the development of an appropriate animal model are desperately needed. The optimal regimen and length of treatment are largely unknown, and with the rising incidence of multidrug-resistant strains of M. tuberculosis, the development of well-tolerated and effective antibiotics remains a continued need. While the most widely used vaccine in the world largely targets this manifestation of tuberculosis, the BCG vaccine has not fulfilled the promise of eliminating CNS tuberculosis. We put forth this review to highlight the current understanding of the neuropathogenesis of M. tuberculosis, to discuss certain epidemiological, clinical, diagnostic, and therapeutic aspects of CNS tuberculosis, and also to underscore the many unmet needs in this important field.

Evaluation of the IS6110 PCR assay for the rapid diagnosis of tuberculous meningitis

Background

Tuberculous meningitis (TBM) is one of the common clinical manifestations of extra-pulmonary tuberculosis. It is difficult to diagnose due to a lack of rapid, sensitive, and specific tests. Newer methods, which are easy and reliable, are required to diagnose TBM at an early stage. Thus our aim was to evaluate the polymerase chain reaction (PCR) technique, using primers directed against the IS6110 gene, for the detection of Mycobacterium tuberculosis in the CSF, for the diagnosis of TBM patients.

Methods

An in-house IS6110 PCR method using a specific pair of primers designed to amplify the insertion sequence, IS6110, in the M. tuberculosis genome was used to analyze CSF. A total of 80 CSF samples from different groups of patients were studied (confirmed TBM n = 35, clinically suspected TBM n = 16, non-TBM infectious meningitis n = 12, non infectious neurological diseases n = 17).

Results

PCR gave a sensitivity of 91.4% and specificity of 75.9% for the diagnosis of TBM in patients with TBM confirmed by culture. In 16 clinically diagnosed, but unconfirmed, TBM cases PCR was positive in 10 (62.5%) cases. There were seven (24.1%) PCR-positive cases among the 29 patients with non-TBM and non-infectious neurological disease.

Conclusion

We conclude that the performance of an in-house IS6110 PCR assay is valuable in the rapid diagnosis of tuberculous meningitis.

Current issues on molecular and immunological diagnosis of tuberculosis

Laboratory diagnosis of tuberculosis (TB) traditionally relies on smear microscopy and culture of Mycobacterium tuberculosis from clinical samples. With recent advances in technology, there have been numerous efforts to develop new diagnostic tests for TB that overcome the low sensitivity and specificity and long turnover time associated with current diagnostic tests. Molecular biological tests based on nucleic acid amplification have brought an unprecedented opportunity for the rapid and specific detection of M. tuberculosis from clinical specimens. With automated sequencing analysis, species identification of mycobacteria is now easier and more accurate than with conventional methods, and rapid detection of mutations in the genes associated with resistance to TB drugs provides early information on the potential drug resistance for each clinical isolate or for clinical samples. In addition, immunological tests for the detection of M. tuberculosis antigens and antibodies to the antigens have been explored to identify individuals at risk of developing TB or with latent TB infection (LTBI). The recent introduction of commercial IFN-gamma assay kits for the detection of LTBI provides a new approach for TB control even in areas with a high incidence of TB. However, these molecular and immunological tools still require further evaluation using large scale cohort studies before implementation in TB control programs.

Rapid diagnosis of tuberculous meningitis: a comparative evaluation of in-house PCR assays involving three mycobacterial DNA sequences, IS6110, MPB-64 and 65 kDa antigen

A PCR was standardized for amplifying three different mycobacterial--IS6110, MPB-64, 65 kDa DNA sequences. A comparative evaluation of the three PCR assays was carried out for the rapid diagnosis of tuberculous meningitis (TBM) using cerebrospinal fluid (CSF) specimens. While the IS6110 PCR was a single-step amplification reaction, the MPB-64 and 65 kDa antigen PCR assays were nested reactions. A total of 176 cerebrospinal fluid (CSF) samples from 176 patients were subjected to amplification of the three different mycobacterial sequences. Amongst them, 45 samples were obtained from confirmed cases of TBM (culture positive) and 56 samples were obtained from clinically suspected cases of TBM which were culture-negative. The remaining 75 CSF samples were categorized under the non-infectious and infectious illness of the central nervous system (CNS). Against a gold standard of culture, a sensitivity of 98% (NPV=99%) and a specificity of 100% (PPV=100%) was observed with the IS6110 PCR. Among the nested PCRs, a sensitivity of 91% (NPV=94%) and a specificity of 91% (PPV=85%) was observed with the MPB-64 assay, while the 65 kDa protocol had an associated sensitivity of 51% (NPV=76%) and a specificity of 92% (PPV=79%). These findings suggest that among the nested PCR assays, the MPB-64 PCR assay was associated with an enhanced degree of sensitivity and was comparable in terms of specificity. Our study also demonstrates that the IS6110 assay, while being a single-step PCR had the advantage of being a rapid test for the diagnosis of TBM, with increased sensitivity and enhanced specificity as compared to the nested PCR protocols.

Comparative evaluation of early diagnosis of tuberculous meningitis by different assays

Cerebrospinal fluid (CSF) and peripheral blood (PBL) were sampled multiple times from 25 patients with a clinical diagnosis of tuberculous meningitis (TBM) and 49 controls, including 27 patients with other infectious diseases of the central nervous system and 22 patients with other noninfectious neurological diseases. We used an enzyme-linked immunospot assay (ELISPOT) to detect anti-Mycobacterium bovis BCG antibody-secreting cells in CSF and PBL, PCR to detect a repeated insertion sequence (IS6110) specific for Mycobacterium tuberculosis in CSF, and an enzyme-linked immunosorbent assay (ELISA) to detect anti-BCG antibodies in CSF and PBL. In the meantime, culture of CSF from every TBM and control patient was done on Lowenstein-Jensen medium. ELISPOT proved to be the most valuable test, with a sensitivity of 84.0% and a specificity of 91.8%, and showed a sensitivity of 100.0% with the CSF specimens obtained within 4 weeks after the onset of TBM. The numbers of CSF anti-BCG immunoglobulin-secreting cells tested by ELISPOT were even higher in the early phase of TBM and declined while the disease was going on (P = 0.008), which allowed an early diagnosis to be made. The sensitivities of PCR and ELISA were only 75.0% and 52.3%, respectively; and the specificities were 93.7% and 91.6%, respectively. Culture of CSF on Lowenstein-Jensen medium was the least sensitive (16%) compared to the sensitivities of the other three assays. Our results demonstrate that the ELISPOT technique is worthy for routine use in the laboratory to support the clinical diagnosis of TBM.

Demonstration of components of antigen 85 complex in cerebrospinal fluid of tuberculous meningitis patients

Tuberculous meningitis (TBM) is the most common form of chronic infection of the central nervous system. Despite the magnitude of the problem, the general diagnostic outlook is discouraging. Specifically, there is no generally accepted early confirmative diagnosis protocol available for TBM. Various Mycobacterium tuberculosis antigens are now recognized as potential markers for diagnosis of TBM. However, their presence remains questionable, and many of these antigens are reported in the blood but not in the cerebrospinal fluid (CSF). This study identifies a specific protein marker in CSF which will be useful in early diagnosis of TBM. We have demonstrated the presence of a 30-kDa protein band in CSF of 100% (n = 5) of confirmed and 90% (n = 138) of suspected TBM patients out of 153 TBM patients. The 30-kDa band was excised from the gel, destained extensively, and digested with trypsin. The resulting peptides were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Partially purified proteins from CSF samples of TBM were analyzed by two-dimensional polyacrylamide gel electrophoresis and Western blotting. Immunoblotting and enzyme-linked immunosorbent assay (ELISA) were performed to confirm the presence of proteins in the 30-kDa protein band. The antigen 85 (Ag 85) complex was detected in CSF of TBM patients by indirect ELISA using antibodies against Ag 85 complex. The results of this study showed the 30-kDa protein band contained MTB proteins Rv3804c (Ag85A) and Rv1886c (Ag 85B), both members of the Ag85 complex. This was also confirmed by using immunotechniques such as indirect ELISA and the dot immunobinding assay. Detection of Ag85 complex was observed in CSF of 89% (71 out of 80) of suspected TBM patients that were 30-kDa protein positive. The observed 30-kDa protein in the CSF is comprised of the MTB Ag85 complex. This protein was earlier reported to be present in the blood of patients with extra-central nervous system tuberculosis. Therefore, this finding suggests that this protein can be used as a molecular marker for any type of tuberculous infection. It also provides a more sensitive immunoassay option for the early and confirmatory diagnosis of TBM.

Molecular genetic methods for diagnosis and antibiotic resistance detection of mycobacteria from clinical specimens

Mycobacteria comprise a diverse group of bacteria that are widespread in nature, some of which cause significant disease in humans. Members of the Mycobacterium tuberculosis complex (MTBC) are the most important human pathogens of the genus Mycobacterium. Traditional methods for detection and identification of mycobacteria include microscopy, culture and phenotypic tests. These methods either lack sensitivity, specificity, or are time consuming. Advances in the field of molecular biology have provided rapid diagnostic tools that have reduced the turnaround times for detecting MTBC and drug resistance in cultures and directly in clinical specimens from weeks to days. This review discusses the molecular genetic techniques for detecting and identifying MTBC as well as drug resistance of mycobacteria in clinical specimens.

Diagnostic accuracy of nucleic acid amplification tests for tuberculous meningitis: a systematic review and meta-analysis

Conventional tests are not always helpful in making a diagnosis of tuberculous meningitis. We did a systematic review and meta-analysis to establish the summary accuracy of nucleic acid amplification (NAA) tests for tuberculous meningitis. We searched six electronic databases and contacted authors, experts, and manufacturers. Measures of diagnostic accuracy were pooled using a random effects model. 49 studies met our inclusion criteria. The summary estimates in 14 studies with commercial NAA tests were: sensitivity 0.56 (95% CI 0.46, 0.66), specificity 0.98 (0.97, 0.99), positive likelihood ratio 35.1 (19.0, 64.6), negative likelihood ratio 0.44 (0.33, 0.60), and diagnostic odds ratio 96.4 (42.8, 217.3). In the 35 studies with in-house ("home-brew") tests, the summary accuracy could not be established with confidence because of wide variability in test accuracy. On current evidence, commercial NAA tests show a potential role in confirming tuberculous meningitis diagnosis, although their overall low sensitivity precludes the use of these tests to rule out tuberculous meningitis with certainty.

Diagnosis of tuberculosis: available technologies, limitations, and possibilities

Rapid diagnosis and treatment are important for preventing transmission of Mycobacterium tuberculosis. However, the diagnosis of tuberculosis continues to pose serious problems, mainly because of difficulties in differentiating between patients with active tuberculosis and those with healed lesions, normal mycobacterium boris BCG (Bacillus Calmette Guerin) vaccinated individuals, and unvaccinated Manteux positives. Physicians still rely on conventional methods such as Ziehl-Neelsen (ZN) staining, fluorochrome staining, sputum culture, gastric lavage, and other non-traditional methods. Although the tuberculin test has aided in the diagnosis of tuberculosis for more than 85 years, its interpretation is difficult because sensitization with nontuberculous mycobacteria leads to false-positive tests. There have been numerous unsuccessful attempts to develop clinically useful serodiagnostic kits for tuberculosis. A number of proteinaceous and nonprotein antigens (such as acyltrehaloses and phenolglycolipids) have been explored from time to time for the development of such assays but they have not proved to be clinically useful. It has been difficult to develop an ELISA utilizing a suitable antigen because M. tuberculosis shares a large number of antigenic proteins with other microorganisms that may or may not be pathogenic. With the advent of molecular biology techniques, there have been significant advances in nucleic acid-based amplification and hybridization, which are helping to rectify existing flaws in the diagnosis of tuberculosis. The detection of mycobacterial DNA in clinical samples by polymerase chain reaction (PCR) is a promising approach for the rapid diagnosis of tuberculous infection. However, the PCR results must be corrected for the presence of inhibitors as well as for DNA contamination. In the modern era of genetics, marked by proteomics and genomics, the day is not far off when DNA chip-based hybridization assays will instantly reveal mycobacterial infections.

[Central nervous tuberculosis in patients non-VIH: seven case reports]

PURPOSE

Tuberculosis involving the central nervous system (CNS) is rarely observed in non immuno-compromised hosts. We report herin the various clinical, biological and radiological manifestations observed in 7 patients with CNS tuberculosis.

METHODS

Clinical and biological records of 7 patients with CNS tuberculosis were retrospectively studied. All patients had encephalic CT-scan and MRI in the course of the disease.

RESULTS

5 women and 2 men with a mean age of 38.4 years initially initially presented with headache (n = 6), fever (n = 5), meningeal irritation (n = 3), localizing neurological signs (n = 1). Lumbar punction revealed lymphocytic meningitis (n = 6/7). Mycobacterium tuberculosis or bovis was isolated in 3 patients only. Cerebral tomodensitography or magnetic resonance imaging were initially normal in most of cases (n = 4/7), but discovered in the course of disease basilar meningitis (n = 6), hydrocephalus (n = 6), abcess or tuberculoma (n = 4). In all the patients, initiation of the treatment was complicated by clinical and/or biological deterioration, called paradoxal reaction, leading in all cases to glucocorticoid adjunction, with various final results. Indeed, 4 patients developed neurological sequelae. No patient died.

CONCLUSION

CNS tuberculosis is a rare disease in non immunocompromised patients whose diagnostic may be difficult due to the absence of specific clinical symptoms, negative initial radiological examination, as well as delayed and often negative bacterial isolation. Paradoxal reaction appeared to be frequent despite specific antibiotherapy and underlines the beneficial effects of addictive corticosteroids.

Approach to the Diagnosis and Management of Tuberculous Meningitis

Meningitis caused by Mycobacterium tuberculosis remains an important cause of morbidity and mortality worldwide, and presents specific challenges in terms of diagnosis and management. The nonspecific clinical presentation of tuberculous meningitis has led researchers to develop newer biochemical and molecular methods of making the diagnosis. Several of these methods have excellent sensitivity and specificity, although are not yet available for clinical use. Successful therapy for tuberculous meningitis requires a combination of antimicrobial agents, with vigilance towards the possibility of disease caused by resistant organisms. Adjunctive corticosteroids also have a role in treating this potentially devastating infection. With proper therapy, morbidity and mortality can be minimized in patients with tuberculous meningitis.