The diagnosis of tuberculosis

Clinical characteristics of tuberculosis-associated immune reconstitution inflammatory syndrome in North Indian population of HIV/AIDS patients receiving HAART

Background & Objective. IRIS is an important complication that occurs during management of HIV-TB coinfection and it poses difficulty in diagnosis. Previous studies have reported variable incidence of IRIS. The present study was undertaken to describe the pattern of TB-associated IRIS using recently proposed consensus case-definitions for TB-IRIS for its use in resource-limited settings. Methods. A prospective analysis of ART-naïve adults started on HAART from November, 2008 to May, 2010 was done in a tertiary care hospital in north India. A total 224 patients divided into two groups, one with HIV-TB and the other with HIV alone, were followedup for a minimum period of 3 months. The diagnosis of TB was categorised as ‘‘definitive” and ‘‘probable”. Results. Out of a total of 224 patients, 203 completed followup. Paradoxical TB-IRIS occurred in 5 of 123 (4%) HIV-TB patients while 6 of 80 (7.5%) HIV patients developed ART-associated TB. A reduction in plasma viral load was significantly (P = .016) associated with paradoxical TB-IRIS. No identifiable risk factors were associated with the development of ART-associated TB. Conclusion. The consensus case-definitions are useful tools in the diagnosis of TB-associated IRIS. High index of clinical suspicion is required for an early diagnosis.

A statistical method was used for the meta-analysis of tests for latent TB in the absence of a gold standard, combining random-effect and latent-class methods to estimate test accuracy

OBJECTIVE

Because of the lack of a gold standard, the diagnostic performance of tests for the detection of latent tuberculosis infection (LTBI) is not known. However, statistical methods can be used to estimate the accuracy from the studies reporting the concordance among the tests.

STUDY DESIGN AND SETTING

We developed a random-effect latent-class model to estimate performance characteristics of three LTBI diagnostic tests: tuberculin skin test (TST, at 10-mm cutoff), QuantiFERON-TB gold (QFG), and TSPOT-TB from the studies evaluating agreement among the tests.

RESULTS

Nineteen studies were included. QFG had a sensitivity of 0.642 (95% confidence interval [CI]: 0.593-0.691) and specificity of 0.996 (95% CI: 0.989-1.000), TSPOT-TB had a sensitivity of 0.500 (95% CI: 0.334-0.666) and specificity of 0.906 (95% CI: 0.882-0.929), and TST had a sensitivity of 0.709 (95% CI: 0.658-0.761) and specificity of 0.683 (95% CI: 0.522-0.844). Results were not sensitive to the inclusion of any single study. When only the three studies that reported on TSPOT were removed, estimates for the other two tests varied minimally.

CONCLUSIONS

Statistical methods can help estimate the accuracy of LTBI tests. Although the specificities were close to their reported values in the literature, the estimates for sensitivities were low; a finding that should be carefully evaluated.

Role of QuantiFERON-TB gold, interferon gamma inducible protein-10 and tuberculin skin test in active tuberculosis diagnosis

Background

The measurement of Interferon gamma or Interferon gamma inducible protein (IP)-10 in antigen stimulated blood samples is suggested as an alternative method for latent tuberculosis (TB) diagnosis. Nonetheless, their role in active TB diagnosis, particularly in TB endemic settings is yet to be defined. In this study, the sensitivities and specificities of Interferon gamma release assay (IGRA), IP-10 assay and tuberculin skin test (TST) in detecting active TB cases were assessed in human immunodeficiency virus (HIV) sero-negative TB patients and healthy controls respectively.

Methods/Principal Findings

A total of 177 adult TB patients and 100 healthy controls were included for this study. QuantiFERON-TB Gold In-tube (QFT-IT) method was used to analyze the sensitivity and specificity of IGRA. QFT-IT, IP-10 and TST yielded the diagnostic sensitivities of 90.6% (95%CI: 86.3%–94.9%), 92.5% (95%CI: 88.6%–96.4%) and 68.9% (95%CI: 60.6%–77.2%) and specificities of 55% (95% CI: 35.2%–54.8%), 48% (95% CI: 38.2%–57.8%) and 75.5% (95% CI: 66.8%–84.2%), respectively. The extent of pulmonary involvement or presence of diabetes mellitus did not appear to influence the sensitivities of any of these tests. The combination of any of the two tests among QFT-IT, IP-10 and TST showed >98% sensitivity among smear negative cases and particularly the combination of IP-10, TST and smear microscopy showed 100% sensitivity, however, the specificity was decreased to 44.8%.

Conclusions/Significance

QFT-IT and IP-10 were highly sensitive in detecting active TB cases. The combination with TST improved the sensitivity of QFT-IT and IP-10 significantly. Although the higher sensitivity of combination of QFT-IT/IP-10 and TST may be useful in active TB diagnosis, they are limited by their poor specificity due to the high prevalence of latent TB in our settings.

Black race, sex, and extrapulmonary tuberculosis risk: an observational study

Background

Extrapulmonary tuberculosis is likely a marker of underlying immune compromise. Our objective was to determine race and sex differences in extrapulmonary tuberculosis risk in order to identify the optimal population in which to assess for host factors associated with extrapulmonary tuberculosis.

Methods

We performed an observational study of all tuberculosis cases reported to the Tennessee Department of Health, January 1, 2000 to December 31, 2006. We compared the incidence of extrapulmonary tuberculosis by race and sex. We also examined risk factors associated with extrapulmonary disease among all persons with tuberculosis.

Results

Extrapulmonary tuberculosis incidence per 100,000 population was 5.93 in black men, 3.21 in black women, 1.01 in non-black men, and 0.58 in non-black women. Among those with tuberculosis, black women were most likely to have extrapulmonary disease (38.6%), followed by black men (28.1%), non-black women (24.6%) and non-black men (21.1%). In multivariate logistic regression among persons with tuberculosis, black women (OR 1.82 (95% CI 1.24-2.65), p = 0.002), black men (OR 1.54 (95% CI 1.13-2.09, p = 0.006), foreign birth (OR 1.55 (95% CI 1.12-2.14), p = 0.009), and HIV infection (OR 1.45 (95% CI 0.99-2.11), p = 0.06) were associated with extrapulmonary tuberculosis.

Conclusions

Black men and black women had the highest incidence of extrapulmonary tuberculosis, and high odds of extrapulmonary disease among persons with tuberculosis. These data suggest that factors in addition to tuberculosis exposure contribute to extrapulmonary tuberculosis risk in blacks.

Cost-effectiveness analysis of PCR for the rapid diagnosis of pulmonary tuberculosis

Background

Tuberculosis is one of the most prominent health problems in the world, causing 1.75 million deaths each year. Rapid clinical diagnosis is important in patients who have co-morbidities such as Human Immunodeficiency Virus (HIV) infection. Direct microscopy has low sensitivity and culture takes 3 to 6 weeks [1-3]. Therefore, new tools for TB diagnosis are necessary, especially in health settings with a high prevalence of HIV/TB co-infection.

Methods

In a public reference TB/HIV hospital in Brazil, we compared the cost-effectiveness of diagnostic strategies for diagnosis of pulmonary TB: Acid fast bacilli smear microscopy by Ziehl-Neelsen staining (AFB smear) plus culture and AFB smear plus colorimetric test (PCR dot-blot).

From May 2003 to May 2004, sputum was collected consecutively from PTB suspects attending the Parthenon Reference Hospital. Sputum samples were examined by AFB smear, culture, and PCR dot-blot. The gold standard was a positive culture combined with the definition of clinical PTB. Cost analysis included health services and patient costs.

Results

The AFB smear plus PCR dot-blot require the lowest laboratory investment for equipment (US$ 20,000). The total screening costs are 3.8 times for AFB smear plus culture versus for AFB smear plus PCR dot blot costs (US$ 5,635,760 versus US$ 1,498, 660). Costs per correctly diagnosed case were US$ 50,773 and US$ 13,749 for AFB smear plus culture and AFB smear plus PCR dot-blot, respectively. AFB smear plus PCR dot-blot was more cost-effective than AFB smear plus culture, when the cost of treating all correctly diagnosed cases was considered. The cost of returning patients, which are not treated due to a negative result, to the health service, was higher in AFB smear plus culture than for AFB smear plus PCR dot-blot, US$ 374,778,045 and US$ 110,849,055, respectively.

Conclusion

AFB smear associated with PCR dot-blot associated has the potential to be a cost-effective tool in the fight against PTB for patients attended in the TB/HIV reference hospital.

Guided sputum sample collection and culture contamination rates in the diagnosis of pulmonary TB

A comparative study to evaluate contamination in cultures of morning sputum samples, comparing those collected at home under currently recommended conditions and those collected under supervision after patient orientation and education. The home and supervised collection groups produced 43 and 76 sputum samples, respectively. The contamination rate was nearly 3-times higher among samples collected at home than among those collected under supervision (37% vs. 13%, p < 0.05; OR = 0.25). The simple educational and hygiene measures described can decrease the contamination rate among sputum samples collected for diagnostic culture.

Recent advances in the diagnosis and treatment of multidrug-resistant tuberculosis

Tuberculosis (TB) is a major infectious disease killing nearly two million people, mostly in developing countries, every year. The increasing incidence of resistance of Mycobacterium tuberculosis strains to the most-effective (first-line) anti-TB drugs is a major factor contributing to the current TB epidemic. Drug-resistant strains have evolved mainly due to incomplete or improper treatment of TB patients. Resistance of M. tuberculosis to anti-TB drugs is caused by chromosomal mutations in genes encoding drug targets. Multidrug-resistant (resistant at least to rifampin and isoniazid) strains of M. tuberculosis (MDR-TB) evolve due to sequential accumulation of mutations in target genes. Emergence and spreading of MDR-TB strains is hampering efforts for the control and management of TB. The MDR-TB is also threatening World Health Organization's target of tuberculosis elimination by 2050. Proper management of MDR-TB relies on early recognition of such patients. Several diagnostic methods, both phenotypic and molecular, have been developed recently for rapid identification of MDR-TB strains from suspected patients and some are also suitable for resource-poor countries. Once identified, successful treatment of MDR-TB requires therapy with several effective drugs some of which are highly toxic, less efficacious and expensive. Minimum treatment duration of 18-24 months is also long, making it difficult for health care providers to ensure adherence to treatment. Successful treatment has been achieved by supervised therapy with appropriate drugs at institutions equipped with facilities for culture, drug susceptibility testing of MDR-TB strains to second-line drugs and regular monitoring of patients for adverse drug reactions and bacteriological and clinical improvement.

Epidemiological profile of tuberculosis cases reported among health care workers at the University Hospital in Vitoria, Brazil

OBJECTIVE

To describe the epidemiological profile of tuberculosis cases reported among health care workers in the Tuberculosis Control Program of the Cassiano Antonio of Moraes University Hospital in Vitoria, Brazil.

METHODS

A retrospective descriptive study of secondary data was conducted between 2002 and 2006.

RESULTS

Twenty-five cases of health care workers with tuberculosis were reported: 8 in nursing technicians (32%); 4 in doctors (16%); 3 in nurses (12%); 2 in radiology technicians (8%) and 8 in professionals from other categories (32%). Of those 25 health care workers, 14 (56%) were male and 11 (44%) were female. The incidence of the disease was highest among those from 35 to 39 years of age. The predominant clinical presentation was extrapulmonary (12 cases, 48%), followed by pulmonary (11 cases, 44%) and a combination of the two (2 cases, 8%). Regarding comorbidities, AIDS, alcoholism and smoking, respectively, were present in 33.3% of the study population. Outcomes were as follows: 22 cases of cure (88%); 2 transfers (8%); and 1 death (4%). The proportion of health care workers diagnosed with tuberculosis in the period studied was 2.53%.

CONCLUSIONS

The results show the need for heath care workers who work in the tuberculosis control program to fill out the field "professional occupation" on the tuberculosis case registry database reporting forms. In addition, this situation draws attention to the need to implement an occupational tuberculosis control program.

Fluoromycobacteriophages for rapid, specific, and sensitive antibiotic susceptibility testing of Mycobacterium tuberculosis

Rapid antibiotic susceptibility testing of Mycobacterium tuberculosis is of paramount importance as multiple- and extensively- drug resistant strains of M. tuberculosis emerge and spread. We describe here a virus-based assay in which fluoromycobacteriophages are used to deliver a GFP or ZsYellow fluorescent marker gene to M. tuberculosis, which can then be monitored by fluorescent detection approaches including fluorescent microscopy and flow cytometry. Pre-clinical evaluations show that addition of either Rifampicin or Streptomycin at the time of phage addition obliterates fluorescence in susceptible cells but not in isogenic resistant bacteria enabling drug sensitivity determination in less than 24 hours. Detection requires no substrate addition, fewer than 100 cells can be identified, and resistant bacteria can be detected within mixed populations. Fluorescence withstands fixation by paraformaldehyde providing enhanced biosafety for testing MDR-TB and XDR-TB infections.

Multidrug-resistant tuberculosis: a review of the 23 cases treated by the Saint-Pierre University Hospital (Brussels)

For about fifteen years, Belgium, as other developed countries, has been confronted with multidrug-resistant tuberculosis (MDR-TB). The treatment of MDR-TB is complex, associating several antibiotics and causing multiple adverse effects. The aim of this study is to report our experience with MDR-TB at the Saint-Pierre University Hospital in Brussels.

Diagnostic usefulness of a T-cell-based assay for extrapulmonary tuberculosis in immunocompromised patients

BACKGROUND

The low reactivity of the tuberculin skin test limits its clinical use in immunocompromised patients with extrapulmonary tuberculosis. A recently developed T-cell-based assay for diagnosing tuberculosis infection gave promising results. However, there were few data on the usefulness of this assay for diagnosing extrapulmonary tuberculosis in immunocompromised patients.

METHODS

All adult patients with suspected extrapulmonary tuberculosis were prospectively enrolled at 2 university-affiliated hospitals over an 18-month period. In addition to the conventional tests for diagnosing extrapulmonary tuberculosis, enzyme-linked immunospot (ELISPOT) assay for the interferon-gamma-producing T-cell response to early secretory antigenic target-6 and culture filtrate protein-10 was performed. The final diagnoses in patients with suspected extrapulmonary tuberculosis were classified by clinical category.

RESULTS

There were 179 patients with suspected extrapulmonary tuberculosis enrolled: 59 (33%) were classified as immunocompromised. Of the 179 patients, 75 (42%) were classified as extrapulmonary tuberculosis, including 56 confirmed tuberculosis plus 19 probable tuberculosis, and 97 (54%) were classified as not tuberculosis. The remaining 7 (4%) had possible tuberculosis and were excluded from the final analysis. The tuberculin skin test (induration size >or=10 mm) was less sensitive in immunocompromised patients (38%; 95% confidence interval [CI], 19%-59%) than in immunocompetent patients (69%; 95% CI, 54%-81%, P=.01). In contrast, the ELISPOT assay retained a high sensitivity: (88%; 95% CI, 68%-97%) in immunocompromised patients compared with 96% (95% CI, 87%-100%) in immunocompetent patients (P=.32).

CONCLUSION

The immunosuppressive condition does not affect the diagnostic sensitivity of the ELISPOT assay for extrapulmonary tuberculosis.

Reversing the tide of tuberculosis in India: complementing microscopy with line probe assays

In 1993, the World Health Organisation (WHO) declared tuberculosis (TB) a global health threat, adopted the Directly Observed Therapy - Short Course (DOTS) strategy, and set two targets for control and elimination of the disease: to detect 70% of sputum smear positive cases and to successfully treat 85% of those cases. The recommended diagnostic tool under DOTS remains sputum smear microscopy, a simple, yet ineffective, technique that only detects roughly half of TB cases. In India, where TB killed 450,000 people in 2005, both WHO targets for detection and treatment were met in the smear positive population covered by DOTS. However, HIV co-infection and multidrug-resistant TB (MDR-TB) pose formidable threats to TB control: TB in HIV-positive patients is often smear-negative, and microscopy cannot detect drug resistance. Although, the reliance on DOTS has proven effective in areas where both HIV prevalence and drug resistance are low, in India, the National TB Programme should consider complementing the antiquated technique of microscopy in order to diagnose smear-negative, extrapulmonary, and MDR-TB cases. Integrating existing rapid molecular diagnostics with the Indian National TB Programme is timely, and would be extremely beneficial to address the two major threats to TB control in the country.

Proposed management of childhood tuberculosis in low-incidence countries

The incidence of childhood tuberculosis continues to decline in central Europe, but due to migration from high incidence countries paediatricians will still be confronted with it. The management of childhood tuberculosis in low-incidence, high-income countries differs from most high-incidence countries. The primary measures for preventing the transmission of tuberculosis to children are the detection of adult source cases, detection of latent TB infection (LTBI) in children by history, tuberculin skin testing and, if necessary and recommended, interferon-gamma release assays. Children with LTBI should receive preventive therapy. The inclusion of tuberculosis in the differential diagnosis of unclear pulmonary and extrapulmonary disease remains important, and tuberculosis has to be managed according to international standards.

Tuberculosis and nontuberculous mycobacterial infections in older adults

Tuberculosis is one of the world's great public health crises. It is estimated by the World Health Organization that roughly one third of the world's populations, or some 2 billion people, are infected with Mycobacterium tuberculosis, the causative agent. More than 8 million people every year develop active tuberculosis disease, and 2 million die as a result. This article reviews tuberculosis and nontuberculous mycobacterial infections in older adults.

Use of an interferon-gamma release assay to diagnose latent tuberculosis infection in foreign-born patients

BACKGROUND

The tuberculin skin test (TST) has a low specificity in the setting of bacille Calmette-Guérin (BCG) vaccination. Interferon-gamma release assays (IGRAs) appear to be more specific but have not been validated in this population under routine clinical conditions. We sought to validate the routine clinical use of the T-SPOT.TB test (Oxford Immunotec; Oxford, UK), an IGRA, in a predominantly foreign-born population with a high rate of BCG vaccination.

METHODS

We compared the TST and the T-SPOT.TB test in 96 subjects at a New York City Department of Health tuberculosis clinic. We aimed to determine which test better predicted being a close contact of a case of active tuberculosis, a surrogate for latent tuberculosis infection.

RESULTS

A positive T-SPOT.TB test result was strongly associated with being a close contact of a case of active tuberculosis after adjustment for potential confounders (adjusted odds ratio, 2.9; 95% confidence interval, 1.1 to 7.3; p = 0.03). A positive TST result was associated with being a contact only in subjects without BCG vaccination (p = 0.02). The T-SPOT.TB test was more specific for being a close contact than the TST (p < 0.001). Specificity in BCG-vaccinated subjects was 3% for the TST compared with 70% for the T-SPOT.TB test (p < 0.001).

CONCLUSIONS

The T-SPOT.TB test is superior in routine clinical use to the TST for identifying high-risk individuals among foreign-born populations with high rates of BCG vaccination.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Rapid diagnostic testing for mycobacterial infections

Tests based on nucleic acid amplification can rapidly detect mycobacteria in clinical samples. These appear to be promising and may change how mycobacterial diseases are diagnosed in the future. Utilization of nucleic acid hybridization and DNA sequencing has enabled the identification of mycobacteria to the species level and detection of mutations associated with antimicrobial resistance. Combining nucleic acid amplification with genotypic identification methods allows detection and identification of mycobacteria directly in clinical samples and, to a limited extent, detection of antimicrobial resistance. IFN-gamma-based assays provide results faster than the tuberculin skin test and address many of its shortcomings, and are thus poised to replace the latter in the coming years.

What is the role of diagnostic laparoscopy in a gastroenterology unit?

BACKGROUND

Diagnostic laparoscopy is known to be a relatively safe invasive procedure. However, its use has decreased owing to the development of imaging techniques, and fewer gastroenterologists now practice diagnostic laparoscopy. Our aim was to examine the role of diagnostic laparoscopy in a gastroenterology unit in the era of advanced imaging techniques.

METHODS

We retrospectively reviewed 855 diagnostic laparoscopy cases. Its safety and efficacy were evaluated for various indications.

RESULTS

No mortality was observed, and complications were noted in ten patients (1.2%). Among the indications were evaluation of chronic liver disease (n = 673), liver tumor (n = 15), ascites of unknown origin and peritoneal disease (n = 142), and staging of intra-abdominal malignancy (n = 25). In patients with chronic liver disease, 461 were diagnosed as having chronic viral hepatitis, based on clinical data including imaging studies, but the diagnosis was changed to cirrhosis after a laparoscopic exam in 69 patients (15.0%). In patients with ascites of unknown origin and peritoneal disease, the diagnostic yield was 87.2% (123/141). In 24 (19.5%) of the 123 patients, the diagnosis changed or the less probable diagnosis was confirmed after laparoscopic examination. The confirmed diagnoses were mainly primary peritoneal disease, including peritoneal tuberculosis, in 17 patients, peritoneal metastatic carcinoma in five, and mesothelioma in two.

CONCLUSIONS

Diagnostic laparoscopy in a gastroenterology unit is safe and useful, especially for confirmation of liver cirrhosis and primary peritoneal disease evaluation.

The IS6110 repetitive DNA element of Mycobacterium tuberculosis is not detected in exhaled breath condensate of patients with active pulmonary tuberculosis

BACKGROUND

A large tertiary referral hospital in inner-city Chicago.

OBJECTIVES

To determine whether the IS6110 repetitive DNA element of Mycobacterium tuberculosis is detected in exhaled breath condensate of patients with newly diagnosed active pulmonary tuberculosis.

METHODS

Ten hospitalized patients with positive Ziehl-Neelson-stained sputum smears were studied. Concurrent sputum cultures for mycobacteria were performed as well. Exhaled breath condensate was collected from each patient within 6 days of initiating antituberculosis chemotherapy (median 1.5 days). These samples were analyzed by polymerase chain reaction (PCR) using primers designed to amplify the IS6110 DNA fragment of M. tuberculosis. Exogenous M. tuberculosis DNA was added to exhaled breath condensate samples to detect PCR inhibitors. Concurrent cultures of exhaled breath condensate for mycobacteria were performed.

RESULTS

M. tuberculosis was identified in 9 of 10 sputum cultures. One isolate was identified as Mycobacterium kansasii. The IS6110 repetitive DNA element of M. tuberculosis was not detected in any of the 10 exhaled breath condensate samples. Exogenous M. tuberculosis DNA added to these samples elicited the characteristic band pattern of M. tuberculosis on agarose gel electrophoresis. No PCR inhibitors were detected. Cultures of exhaled breath condensate showed no growth of mycobacteria.

CONCLUSIONS

The IS6110 repetitive DNA element of M. tuberculosis is not detected in exhaled breath condensate of patients with newly diagnosed active pulmonary tuberculosis.

Implementation validation performed in Rwanda to determine whether the INNO-LiPA Rif.TB line probe assay can be used for detection of multidrug-resistant Mycobacterium tuberculosis in low-resource countries

We validated the implementation of the INNO-LiPA Rif.TB line probe assay, a diagnostic test for rapid detection of multidrug-resistant tuberculosis (MDR-TB), in Rwanda. No substantial difference was found between results obtained in Rwanda and results obtained in Belgium with the same samples. This rapid diagnostic test for MDR-TB can therefore be reliably implemented in a resource-poor setting.

T-cell assays for the diagnosis of latent tuberculosis infection: moving the research agenda forward

For nearly a century, the tuberculin skin test was the only tool available for the detection of latent tuberculosis infection. A recent breakthrough has been the development of T-cell-based interferon-gamma release assays. Current evidence suggests interferon-gamma release assays have higher specificity than the tuberculin skin test, better correlation with surrogate markers of exposure to Mycobacterium tuberculosis in low-incidence settings, and less cross-reactivity as a result of BCG vaccination compared with the tuberculin skin test. The body of literature supporting the use of interferon-gamma release assays has rapidly expanded. However, several unresolved and unexplained issues remain. To address these issues, a group of experts met in Geneva, Switzerland, in March, 2006, to discuss the research evidence on T-cell-based assays, their clinical usefulness, limitations, and directions for future research, with a specific focus on resource-limited and high HIV prevalence settings. On the basis of 2 days of discussions, a comprehensive research agenda was generated, which will propel the field forward by stimulating focused high-impact research and encourage the investment of resources needed to tackle priority research questions, especially in resource-limited settings. Ultimately, if adequately financed, the research findings will inform appropriate use of novel latent tuberculosis infection diagnostics in global tuberculosis control.

Messenger RNA expression of IL-8, FOXP3, and IL-12beta differentiates latent tuberculosis infection from disease

Differentiation of active from latent tuberculosis (TB) is a major challenge in the control of TB. In this study, PBMC from latent TB-infected subjects, TB patients, and tuberculin skin test-negative donors stimulated with the Mycobacterium tuberculosis (Mtb)-specific Ag, early secretory antigenic target 6, and mRNA for 45 immune-related genes was measured by quantitative real-time PCR. Univariate analysis showed significant differences in the expression of 10 genes (IFN-gamma, FOXP3, IL-1alpha, IL-1beta, IL-2, IL-6, IL-8, IL-12alpha, IL-12beta, and IL-24) in PBMC from TB patients vs latent TB-infected subjects (p < 0.01). Multivariate logistic regression and classification and regression tree analyses revealed that expression of three genes, IL-8, FOXP3, and IL-12beta, is predictive for TB vs latent Mtb infection. Thus, measurement of Ag-specific expression of these three genes may offer a specific and noninvasive means of differentiating between latent Mtb infection and TB.

Analysis of latent tuberculosis and mycobacterium avium infection data using mixture models

BACKGROUND

Estimation of the frequency of latent tuberculosis infection (LTBI) is difficult in areas with low tuberculosis infection rates and high exposure to non-tuberculous mycobacteria (NTM), including BCG vaccination. The objective was to assess LTBI and M avium infection and to estimate their probability based on skin tests responses in an infant population from a region with the aforementioned characteristics.

METHODS

A population-based tuberculin skin test (TST) and sensitin (M avium) survey was conducted on seven years old infants in Biscay, a province from The Basque Country (Spain). 2268 schoolchildren received sensitin and 5277 TST. Participation rate was 89%. Commonly used estimation methods were compared with a method based on the fit of mixture models using the Expectation Maximization algorithm. Functions estimating the probabilities of LTBI and M avium infection given the observed skin tests responses were developed for vaccinated and unvaccinated children.

RESULTS

LTBI prevalences varied widely according to the estimation method. The mixture model provided prevalences higher than expected although intermediates between those obtained by currently recommended approaches. Exposure to previous BCG vaccine produces an upward shift of an average of about 3 mm on the induration size to attain the same probability of infection.

CONCLUSION

Our results confirm the commonplace exposure to NTM which effect should be taken into account when performing and assessing tuberculin surveys. The use of mixture analysis under the empirical Bayes framework allows to better estimate the probability of LTBI in settings with presence of other NTM and high BCG-vaccination coverage. An estimation of the average effect of BCG vaccination on TST induration is also provided. These models maximise information coming from classical tuberculin surveys and could be used together with the newly developed blood tests to improve survey's specificity and cost-effectiveness.

New tools and emerging technologies for the diagnosis of tuberculosis: part I. Latent tuberculosis

Nearly a third of the world's population is estimated to be infected with Mycobacterium tuberculosis. This enormous pool of latently infected individuals poses a major hurdle for global tuberculosis (TB) control. Currently, diagnosis of latent TB infection (LTBI) relies on the tuberculin skin test (TST), a century-old test with known limitations. In this review, the first of a two-part series on new tools for TB diagnosis, recent advances in the diagnosis of LTBI are described. The biggest advance in recent years has been the development of in vitro T-cell-based interferon-gamma release assays (IGRAs) that use antigens more specific to M. tuberculosis than the purified protein derivative used in the TST. Available research evidence on IGRAs suggests they have higher specificity than TST, better correlation with surrogate markers of exposure to M. tuberculosis in low-incidence settings, and less cross-reactivity due to BCG vaccination than the TST. IGRAs also appear to be at least as sensitive as the purified protein derivative-based TST for active TB. In the absence of a gold standard for LTBI, sensitivity and specificity for LTBI are not well defined. Besides high specificity, other potential advantages of IGRAs include logistical convenience, avoidance of poorly reproducible measurements, such as skin induration, need for fewer patient visits and the ability to perform serial testing without inducing the boosting phenomenon. Overall, due to its high specificity, IGRAs may be useful in low-endemic, high-income settings where cross-reactivity due to BCG might adversely impact the utility of TST. However, despite the growing evidence supporting the use of IGRAs, several unresolved and unexplained issues remain. The review concludes by highlighting areas where evidence is lacking, and provides an agenda for future research. Active TB and drug resistance are discussed in Part II; 423-432 of this issue.

New tools and emerging technologies for the diagnosis of tuberculosis: part II. Active tuberculosis and drug resistance

Tuberculosis (TB) is one of the world's most important infectious causes of morbidity and mortality among adults. Between 8 and 9 million develop TB disease, and approximately 2 million die from TB each year. Despite this enormous global burden, case detection rates are low, posing major hurdles for TB control. Conventional TB diagnosis continues to rely on smear microscopy, culture and chest radiography. These tests have known limitations. Conventional tests for detection of drug resistance are slow, tedious and difficult to perform in field conditions. This second half of a two-part review series on new tools for TB diagnosis describes recent advances and emerging technologies in the diagnosis of active disease, and detection of drug resistance. For diagnosis, new tools include newer versions of nucleic acid amplification tests, immune-based assays, skin patch test and rapid culture systems. For drug resistance, new tools include line-probe assays, bacteriophage-based assays, molecular beacons and microscopic observation drug susceptibility assay. Although the ideal test for TB is still not in sight, substantial progress has been made in the past decade. With the resurgence of interest in the development of new tools for TB control, it is likely that the next decade will see greater progress and tangible benefits. However, the challenge will be to ensure that new tools undergo rigorous evaluations in field conditions, and also to make sure that benefits of promising new tools actually reach the populations in developing countries that need them most. Latent TB is discussed in Part I; 413-422 of this issue.

Antimycobacterial Agents. Novel Diarylpyrrole Derivatives of BM212 Endowed with High Activity toward Mycobacterium tuberculosis and Low Cytotoxicity

On the basis of suggestions derived either from a pharmacophoric model for antitubercular agents or from a structure-activity relationship analysis of many pyrroles previously described by us, we report here the design and synthesis of new analogues of 1,5-(4-chlorophenyl)-2-methyl-3-(4-methylpiperazin-1-yl)methyl-1H-pyrrole (BM212). Various substituents with different substitution patterns were added to both positions 1 and 5 of the pyrrole nucleus to evaluate their influence on the activity toward Mycobacterium tuberculosis (MTB) and atypical mycobacteria. Biological data showed that, although some nontuberculosis mycobacterial strains were found to be sensitive, MIC values were higher than those found toward MTB. The best compound (1-(4-fluorophenyl)-2-methyl-3-(thiomorpholin-4-yl)methyl-5-(4-methylphenyl)-1H-pyrrole, 5) possessed a MIC of 0.4 microg/mL (better than BM212 and streptomycin) and a very high protection index (160), better than BM212, isoniazid, and streptomycin (6, 128, and 128, respectively). Finally, molecular modeling studies were performed to rationalize the activity of the new compounds in terms of both superposition onto a pharmacophoric model for antitubercular compounds and their hydrophobic character.

Advances in the diagnosis and treatment of tuberculosis

Although truly major advances that would revolutionize tuberculosis (TB) diagnosis and treatment have not been realized, we are beginning to see the innovations that have been prompted by the recognition of the economic potential of the market for new diagnostic tests and treatments for TB and considerably increased public and private funding. Despite the enormous global burden of TB and the overall low rates of case detection worldwide, conventional approaches to diagnosis have, until recently, relied on tests that have major limitations. In this review of advances in diagnosis, we focus on strengths and limitations of newer tests that are available for the diagnosis of latent and active tuberculosis and rapid detection of drug resistance, specifically, tests that measure release of IFN-gamma in response to stimulation by Mycobacterium tuberculosis antigens, nucleic acid amplification for identification of M. tuberculosis complex, and rapid tests for detecting drug resistance. Standard regimens for treating TB have not changed for more than 30 yr and still require a minimum of 6 mo to have a high likelihood of a lasting cure. In this article, we focus on important changes in the philosophy of treatment, emphasizing the responsibility of the provider to assure successful completion of treatment, and on the roles of existing anti-TB agents and newer drugs such as rifabutin, rifapentine, and fluoroquinolones.

In house reverse line hybridization assay for rapid detection of susceptibility to rifampicin in isolates of Mycobacterium tuberculosis

We developed a Reverse Hybridization Assay (RHA) slightly modified from the Rifoligotyping assay and analyzed the presence of mutations in a specific region of rpoB gene in 157 isolates (90 rifampin-resistant and 67 rifampin sensitive) of Mycobacterium tuberculosis from patients attended in South and Southeast region of Brazil. Comparing to standardized drug susceptibility testing results, the sensitivity and specificity of the RHA was respectively 93% (95% IC: 86.6%-97.2%) and 100% respectively. Additionally, a high agreement (kappa coefficient 95%) between the RHA assay and sequencing was obtained. Among the 90 rifampicin-resistant isolates, RHA identified point mutations in the following codons: 42 isolates (46.6%) in 531; 29 isolates (32.2%) in 526, 6 isolates (6.7%) in 516, 3 isolates (3.3%) in 522, 2 isolates (2.2%) in 515, 514, 513 and 1 isolate (1.1%) in 511, 524 and 525. Mutations in different codons were simultaneously identified in 8 isolates (8.9%). The RHA used in the present study had a high accuracy and can be rapidly performed. However, more reproducible hybridization conditions should be looked for to increase reliability of mutant probe interpretation.