Comparison of Two Interferon-γ Assays and Tuberculin Skin Test for Tracing Tuberculosis Contacts

Tuberculous spondylitis in patients with end-stage renal disease undergoing chronic hemodialysis therapy — Report of two cases

Tuberculous spondylitis is more common in patients with chronic renal failure who receive hemodialysis because of their abnormal T-cell-mediated immunity. It frequently poses both diagnostic and therapeutic challenges. We describe two cases of tuberculous spondylitis in patients undergoing chronic hemodialysis therapy. They are IFN-γ assay diagnosed (QuantiFERON-TB Gold) and conservatively treated. Our cases suggest that IFN-γ assays equip clinicians with more accurate tools for tuberculosis control. A combination of T-SPOT.TB testing and MRI assessment may be the accurate method to diagnose tuberculous spondylitis in patients with end-stage renal disease.

IFN-gamma-release assays in the management of tuberculosis

New blood tests for TB are now available. One measures the release of IFN-gamma and the other estimates the number of cells secreting IFN-gamma after stimulation with antigens from Mycobacterium tuberculosis. The choice of antigens (esat-6 and cfp-10) is intended to distinguish TB infection from Bacille Calmette-Guerin vaccination. Tests differ in lymphocyte numbers, the use of an additional antigen (TB7.7 - Rv2654) and sensitivity in concurrent HIV infection. Their role in the routine diagnosis of TB is limited. In latent TB infection, the new tests correlate better with exposure to TB. However, the time course of the immune response, the significance of negative tests, conversions from positive to negative and vice versa and their value in predicting who will develop TB are not yet known. Prospective studies of these tests are needed to establish their practical value rather than theoretical role in latent TB infection. Cohorts of both immunocompetent and immunosuppressed subjects who may develop active disease should be examined.

T-Spot.TB outperforms tuberculin skin test in predicting tuberculosis disease

RATIONALE

Silicosis is a well-recognized risk factor for tuberculosis (TB).

OBJECTIVES

To compare T-Spot.TB with tuberculin skin test (TST) in predicting the development of TB.

METHODS

Male patients with silicosis without clinical suspicion of active TB, past history of TB, and treatment for latent TB infection (LTBI) were offered both T-Spot.TB and TST in the Pneumoconiosis Clinic of Hong Kong from 2004 to 2008, and followed prospectively until September 30, 2009, for development of TB.

MEASUREMENTS AND MAIN RESULTS

Active TB and culture- or histology-confirmed TB developed in 17 (5.5%) and 14 (4.5%) of 308 recruited subjects at an annual rate of 2,247 and 1,851 per 100,000 person-years, respectively. Active TB occurred in 7.4% (15 of 204) and 1.9% (2 of 104) of T-Spot.TB-positive and -negative subjects, respectively, whereas the corresponding figures for TST (cutoff 10 mm) were 6.4% (13 of 203) and 3.9% (4 of 205), respectively. A positive T-Spot.TB test significantly predicted the subsequent development of active TB (relative risk, 4.50; 95% confidence interval, 1.03-19.68) and culture- or histology-confirmed TB (relative risk, 7.80; 95% confidence interval, 1.02-59.63). Consistent results were obtained after exclusion of subjects treated for LTBI and adjustment for potential confounders. TST did not significantly predict the development of active TB or culture- or histology-confirmed TB, irrespective of the cutoff values with or without exclusion of subjects treated for LTBI. Culture filtrate protein 10 spot count, but not early secretary antigenic target 6 spot count, was significantly associated with subsequent TB development.

CONCLUSIONS

T-Spot.TB performs better than TST in the targeted screening of LTBI among patients with silicosis.

Commercial interferon gamma release assays compared to the tuberculin skin test for diagnosis of latent Mycobacterium tuberculosis infection in childhood contacts in the Gambia

BACKGROUND

We compared the performance of tuberculin skin test (TST), Quantiferon-TB Gold in-tube (QFT-GIT), and T-SPOT.TB in diagnosing latent tuberculosis (LTBI) among childhood TB contacts in a TB endemic setting with high BCG coverage. We evaluated the performance of interferon gamma release assays (IGRAs) and TST when combined in an algorithm.

METHODS

Childhood contacts of newly diagnosed TB patients were tested with TST, QFT-GIT, and T-SPOT. The level of exposure in contacts was categorized according to whether they slept in the same room, same house, or a different house as the index case. For the evaluation of combined test performance, prior estimates for prevalence of latent TB were used in Bayesian models that assumed conditional dependence between tests.

RESULTS

A total of 285 children were recruited. Overall, 26.5%, 33.0%, and 33.5% were positive for TST, T-SPOT, or QFT-GIT, respectively. All 3 tests responded to the gradient of sleeping proximity to the index case. Neither TST nor IGRA results were confounded by BCG vaccination. There was moderate agreement (kappa = 0.40-0.68) between all 3 tests. Combination of either IGRA with TST increased sensitivity (by 9.3%-9.6%) especially in contacts in the highest exposure category but was associated with loss of specificity (9.9%-11.3%).

CONCLUSION

IGRAs and TST are similar in their diagnostic performance for LTBI. An approximate 10% sensitivity benefit for using the TST and an IGRA in combination is associated with a slightly greater specificity loss. Testing strategies combining an IGRA and TST with an "or" statement may be useful only in situations where there is a high pretest probability of latent infection.

Interpreting tuberculin skin tests in a population with a high prevalence of HIV, tuberculosis, and nonspecific tuberculin sensitivity

Understanding the epidemiology and clinical course of tuberculosis is hampered by the absence of a perfect test for latent tuberculosis infection. The tuberculin skin test (TST) is widely used but suffers poor specificity in those receiving the bacille Calmette-Guérin vaccine and poor sensitivity in individuals with human immunodeficiency virus (HIV) infections. TST responses for a target population in Harare, Zimbabwe (HIV prevalence, 21%), recruited in 2005–2006, were interpreted by using a separate calibration population in Harare, for which interferon-gamma release assays (enzyme-linked immunosorbent spot (ELISpot)) results were also known. Statistical fitting of the responses in the calibration population allowed computation of the probability that an individual in the target population with a given TST and HIV result would have tested ELISpot positive. From this, estimates of the prevalence of tuberculosis infection, and optimal TST cutpoints to minimize misdiagnosis, were computed for different assumptions about ELISpot performance. Different assumptions about the sensitivity and specificity of ELISpot gave a 40%–57% prevalence of tuberculosis infection in the target population (including HIV-infected individuals) and optimal TST cutpoints typically in the 10 mm–20 mm range. However, the optimal cutpoint for HIV-infected individuals was consistently 0 mm. This calibration method may provide a valuable tool for interpreting TST results in other populations.

Comparison of T-cell interferon-gamma release assays for Mycobacterium tuberculosis-specific antigens in patients with active and latent tuberculosis

Through the use of QuantiFERON-TB Gold, a commercial IFN-γ assay, we compared differences in quantitative T-cell responses to Mycobacterium tuberculosis (MTB)-specific antigens [QuantiFERON TB-2G (QFT-2G)] between patients with active tuberculosis (TB) disease and those with latent TB infection (LTBI). The patient group consisted of 180 patients with active TB disease (culture-positive for MTB) and 50 screening contacts with LTBI-positive response to the QFT-2G test. We prospectively performed a tuberculin skin test (TST) and a QFT-2G test for all subjects. The median IFN-γ levels upon the application of both antigens, ESAT-6 and CFP-10, were significantly higher in patients with active TB disease than in those with LTBI. A combined positive response to both antigens occurred at a higher rate in patients with active TB disease than in those with LTBI. There were no significant relationships between the quantitative responses of IFN-γ to both antigens and the maximum induration on TST in both patient groups. We demonstrated significant differences in the quantitative responses of IFN-γ to MTB between patients with active TB disease and those with LTBI in this study. However, there was an overlap in the IFN-γ levels between active TB disease and LTBI groups. Therefore, it would be difficult to use the QFT-2G test to completely discriminate active TB disease from LTBI.

Kinetics of a tuberculosis-specific gamma interferon release assay in military personnel with a positive tuberculin skin test

Treatment of latent Mycobacterium tuberculosis infection on the basis of the tuberculin skin test (TST) result is inaccurate due to the false-positive TST results that occur after Mycobacterium bovis BCG vaccination or exposure to nontuberculous mycobacteria (NTM). Gamma interferon release assays (IGRAs) are based on M. tuberculosis-specific antigens. In a previous study among BCG-naïve military employees, a positive TST result after deployment was mostly associated with a negative IGRA result, suggesting exposure to NTM. Data regarding the kinetics of IGRAs are limited and controversial. The present study aimed to reassess the rate of false-positive TST results and to evaluate the kinetics of the Quantiferon TB Gold In-Tube assay (QFT-Git) in military personnel with a positive TST result. QFT-Git was performed at the time of inclusion in the study and was repeated after 2, 6, 12, and 18 or 24 months. Of 192 participants, 17 were recruits and 175 were screened after deployment (n = 169) or because of travel or health care work. Baseline positive QFT-Git results were observed in 7/17 (41.2%) and 12/174 (6.9%) participants, respectively. During follow-up, a negative QFT-Git result remained negative in 163/165 (98.8%) participants. Of 18 subjects with an initial positive QFT-Git result, reversion to a negative result occurred in 1/6 (16%) recruits, whereas it occurred in 8/12 (66%) subjects after deployment or with other risk factors (P = 0.046). The quantitative result was significantly lower in subjects with reversion than in those with consistent positive results (P = 0.017). This study confirmed a low rate of positive QFT-Git results among military personnel with a positive TST result after deployment, supporting the hypothesis of exposure to NTM. Reversion of the majority of initially low-positive QFT-Git results indicates that QFT-Git may be useful for the diagnosis of later reinfections.

Diagnosis and follow-up of treatment of latent tuberculosis; the utility of the QuantiFERON-TB Gold In-tube assay in outpatients from a tuberculosis low-endemic country

Background

Interferon-gamma (IFN-γ) Release Assays (IGRA) are more specific than the tuberculosis skin test (TST) in the diagnosis of latent tuberculosis (TB) infection (LTBI). We present the performance of the QuantiFERON^®-TB Gold In-tube (QFT-TB) assay as diagnostic test and during follow-up of preventive TB therapy in outpatients from a TB low-endemic country.

Methods

481 persons with suspected TB infection were tested with QFT-TB. Thoracic X-ray and sputum samples were performed and a questionnaire concerning risk factors for TB was filled. Three months of isoniazid and rifampicin were given to patients with LTBI and QFT-TB tests were performed after three and 15 months.

Results

The QFT-TB test was positive in 30.8% (148/481) of the total, in 66.9% (111/166) of persons with origin from a TB endemic country, in 71.4% (20/28) previously treated for TB and in 100% (15/15) of those diagnosed with active TB with no inconclusive results. The QFT-TB test was more frequently positive in those with TST ≥ 15 mm (47.5%) compared to TST 11-14 mm (21.3%) and TST 6-10 mm (10.5%), (p < 0.001). Origin from a TB endemic country (OR 6.82, 95% CI 1.73-26.82), recent stay in a TB endemic country (OR 1.32, 95% CI 1.09-1.59), duration of TB exposure (OR 1.59, 95% CI 1.14-2.22) and previous TB disease (OR 11.60, 95% CI 2.02-66.73) were all independently associated with a positive QFT-TB test. After preventive therapy, 35/40 (87.5%) and 22/26 (84.6%) were still QFT-TB positive after three and 15 months, respectively. IFN-γ responses were comparable at start (mean 6.13 IU/ml ± SD 3.99) and after three months (mean 5.65 IU/ml ± SD 3.66) and 15 months (mean 5.65 IU/ml ± SD 4.14), (p > 0.05).

Conclusion

Only one third of those with suspected TB infection had a positive QFT-TB test. Recent immigration from TB endemic countries and long duration of exposure are risk factors for a positive QFT-TB test and these groups should be targeted through screening. Since most patients remained QFT-TB positive after therapy, the test should not be used to monitor the effect of preventive therapy. Prospective studies are needed in order to determine the usefulness of IGRA tests during therapy.

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.

Quantitative evaluation of T-cell response after specific antigen stimulation in active and latent tuberculosis infection in adults and children

We have evaluated the quantitative T-cell response after specific Mycobacterium tuberculosis antigen stimulation in active tuberculosis (TB) and latent TB infection (LTBI) patients. In adults, the median number of T cells after RD1 antigen stimulation was significantly higher in active TB patients than in LTBI patients. In children, the number of responder T cells against the specific antigens was higher in active TB than in LTBI patients, although the differences were not significant. In summary, in patients with suspected clinical TB, although there is overlapping in the number of responder T cells between both groups, a T-cell count above the described threshold could suggest active TB, especially in patients with a high probability of having active TB and low probability of having LTBI. In addition, the results are consistent with the current evidence that T-cell response may indicate mycobacterial burden and disease activity.

Interferon-gamma release assays: new diagnostic tests for Mycobacterium tuberculosis infection, and their use in children

PURPOSE OF REVIEW

The testing and treatment of children at risk for Mycobacterium tuberculosis infection represents an important public health priority in the United States. Until recently, diagnosis has relied upon the tuberculin skin test (TST). New interferon-gamma release assays (IGRAs) offer improvements over TST, but these tests have not been studied in children until recently.

RECENT FINDINGS

Evidence regarding IGRA performance in children is accumulating rapidly. Overall, the findings demonstrate performance of IGRAs equivalent or superior to that of the TST. However, IGRAs have biological limitations similar to TST and some technical problems of their own, and critical gaps in our knowledge remain.

SUMMARY

Current evidence supports usage of IGRAs in children aged 5 years or older. IGRAs are preferred over TST when specificity is paramount or wherein patients might fail to return for TST reading. Evidence for use in children aged less than 5 years is insufficient at this time: the sensitivity is poorly defined, and TST is preferred for testing these children. Future IGRA research should focus on children aged less than 5 years for informing expanded usage in this vulnerable population.

A 100 year update on diagnosis of tuberculosis infection

BACKGROUND

Diagnosis and treatment of latent tuberculosis infection (LTBI) is a cornerstone of tuberculosis (TB) control in the developed world. In the last century, the tuberculin skin test (TST) was the only means of diagnosing LTBI. ELISpot and whole-blood ELISA, collectively known as interferon-gamma release assays (IGRAs), are promising new tools.

AREAS OF AGREEMENT

IGRAs are more specific than TST for diagnosis of LTBI as they are not confounded by previous bacille Calmette-Guerin (BCG) vaccination. Assessing IGRA sensitivity in the absence of a gold standard for LTBI is challenging. Studies have therefore used surrogate markers such as active TB and correlation with degree of TB exposure in contact investigations. These studies suggest that sensitivity of ELISpot is higher than TST while whole-blood ELISA has similar sensitivity to TST. Recent longitudinal studies demonstrating the prognostic power of these tests for development of active TB provide definitive evidence that positive IGRA results reflect infection with dormant yet viable bacilli.

AREAS OF CONTROVERSY

Is the prognostic power of IGRAs greater than the TST? What are the false-negative rates in immunocompromised individuals with LTBI at high risk of progressing to active TB?

GROWING POINTS

IGRAs have been incorporated into national guidelines, although their optimal deployment in diagnostic algorithms is evolving. The health economic benefits of utilizing IGRAs are increasingly recognized, partly because their high specificity avoids unnecessary chemoprophylaxis in BCG-vaccinated persons with false-positive TST results.

AREAS TIMELY FOR DEVELOPING RESEARCH

Current IGRAs are being improved and next-generation tests, with improved sensitivity, could enable the reliable exclusion of LTBI in immunocompromised individuals.

Comparison of interferon {gamma} release assays and conventional screening tests before tumour necrosis factor {alpha} blockade in patients with inflammatory arthritis

OBJECTIVE

To compare the performance of two interferon gamma release assays (IGRAs) and conventional screening tests in patients with inflammatory arthritis undergoing screening for latent tuberculosis infection (LTBI) before treatment with anti-tumour necrosis factor alpha (anti-TNFalpha) compounds.

METHODS

Successive patients were subjected to conventional LTBI screening, including a tuberculin skin test (TST). The T-SPOT.TB test was performed on all patients and the QuantiFERON-TB Gold test was performed on a large subset. The results of the IGRAs were compared with the results of conventional screening tests.

RESULTS

A total 150 patients were evaluated. The majority (57.9%) had rheumatoid arthritis. Previous vaccination with Bacille Calmette-Guerin was confirmed in 82% of patients. No patient had received prior anti-TB treatment. A total of 57 patients (38.0%) had at least one positive conventional risk factor. In contrast, an unequivocally positive T-SPOT.TB test was seen in only 14/143 (9.8%). There was 98.2% agreement between the two IGRAs. Statistically significant associations were found between each of the IGRAs and both TST and risk history, but not chest x-ray (CXR). A positive IGRA result was significantly associated with increased age. TB was not reactivated in any patient during the follow-up period.

INTERPRETATION

This study suggests that IGRAs may be useful when screening for LTBI before anti-TNFalpha therapy in patients with immune-mediated inflammatory diseases. The observations reported here also highlight the inadequate performance of CXR as a marker of LTBI.

Evidence-based comparison of commercial interferon-gamma release assays for detecting active TB: a metaanalysis

Test accuracy of interferon-gamma release assays (IGRAs) for diagnosing TB differs when using older or precommercial tools and inconsistent diagnostic criteria. This metaanalysis critically appraises studies investigating sensitivity and specificity of the commercial T-Spot.TB and the QuantiFERON-TB Gold In-Tube Assay (QFT-IT) among definitely confirmed TB cases. We searched Medline, EMBASE, and Cochrane bibliographies of relevant articles. Sensitivities, specificities, and indeterminate rates were pooled using a fixed effect model. Sensitivity of the tuberculin skin test (TST) was evaluated in the context of IGRA studies. In addition, the rates of indeterminates of both IGRAs were assessed. The pooled sensitivity of TST was 70% (95% CI, 0.67-0.72) compared with 81% (95% CI, 0.78-0.83) for the QFT-IT and 88% (95% CI, 0.85-0.90) for the T-Spot.TB. Sensitivity increased to 84% (95%CI, 0.81-0.87) and 89% (95% CI, 0.86-0.91) for the QFT-IT and T-Spot.TB, respectively, when restricted to performance in developed countries. In contrast, specificity of the QFT-IT was 99% (95% CI, 0.98-1.00) vs 86% for the T-Spot.TB (95% CI, 0.81-0.90). The pooled rate of indeterminate results was low, 2.1% (95% CI, 0.02-0.023) for the QFT-IT and 3.8% (95% CI, 0.035-0.042) for the T-Spot.TB, increasing to 4.4% (95% CI, 0.039-0.05) and 6.1% (95% CI, 0.052-0.071), respectively, among immunosuppressed hosts. The newest commercial IGRAs are superior, in comparison with the TST, for detecting confirmed active TB disease, especially when performed in developed countries.

An update on primary care management for tuberculosis in children

PURPOSE OF REVIEW

Tuberculosis (TB) is still a significant cause of mortality and morbidity among children worldwide. Recent advances in scientific and clinical research have looked into the epidemiology, diagnostic, therapeutic and preventive interventions in order to provide insights into more effective control.

RECENT FINDINGS

The risk of infection has been shown to be related to the duration and proximity of exposure to an infectious case, usually an adult or adolescent, rising with increased exposure in toddlers, associated with school entry, and in the teen years and early adulthood. Initial primary exposure to TB disease plays a significant role in the development of a latent TB infection, which may serve as a reservoir for future reactivation in adulthood. Diagnosis remains a dilemma for the clinician due to the lack of a gold standard. T-cell assays measuring production of interferon gamma have proven to be more specific than the Tuberculin Skin Test but are unable to distinguish between latent and active disease.

SUMMARY

Recent findings have shown the importance of addressing not only active TB disease in children but also latent TB infection. Advances in understanding TB in children provide insights to enhance efforts to control this disease.

New tools for detecting latent tuberculosis infection: evaluation of RD1-specific long-term response

Background

Interferon-gamma (IFN-γ) release assays (IGRAs) were designed to detect latent tuberculosis infection (LTBI). However, discrepancies were found between the tuberculin skin test (TST) and IGRAs results that cannot be attributed to prior Bacille Calmètte Guerin vaccinations. The aim of this study was to evaluate tools for improving LTBI diagnosis by analyzing the IFN-γ response to RD1 proteins in prolonged (long-term response) whole blood tests in those subjects resulting negative to assays such as QuantiFERON-TB Gold In tube (QFT-IT).

Methods

The study population included 106 healthy TST⁺ individuals with suspected LTBI (recent contact of smear-positive TB and homeless) consecutively enrolled. As controls, 13 healthy subjects unexposed to M. tuberculosis (TST^-, QFT-IT^-) and 29 subjects with cured pulmonary TB were enrolled. IFN-γ whole blood response to RD1 proteins and QFT-IT were evaluated at day 1 post-culture. A prolonged test evaluating long-term IFN-γ response (7-day) to RD1 proteins in diluted whole blood was performed.

Results

Among the enrolled TST⁺ subjects with suspected LTBI, 70/106 (66.0%) responded to QFT-IT and 64/106 (60.3%) to RD1 proteins at day 1. To evaluate whether a prolonged test could improve the detection of LTBI, we set up the test using cured TB patients (with a microbiologically diagnosed past pulmonary disease) who resulted QFT-IT-negative and healthy controls as comparator groups. Using this assay, a statistically significant difference was found between IFN-γ levels in cured TB patients compared to healthy controls (p < 0.006). Based on these data, we constructed a receiver operating characteristic (ROC) curve and we calculated a cut-off. Based on the cut-off value, we found that among the 36 enrolled TST+ subjects with suspected LTBI not responding to QFT-IT, a long term response to RD1 proteins was detected in 11 subjects (30.6%).

Conclusion

These results indicate that IFN-γ long-term response to M. tuberculosis RD1 antigens may be used to detect past infection with M. tuberculosis and may help to identify additional individuals with LTBI who resulted negative in the short-term tests. These data may provide useful information for improving immunodiagnostic tests for tuberculosis infection, especially in individuals at high risk for active TB.

Serial interferon-gamma release assays after rifampicin prophylaxis in a tuberculosis outbreak

Even though some studies have reported the results of serial interferon-gamma release assays (IGRAs) during isoniazid prophylactic treatment, serial results have not been reported after rifampicin prophylaxis. A contact investigation was conducted after a tuberculosis (TB) outbreak in an accommodation facility. The tuberculin skin test (TST) and the QuantiFERON-TB Gold In-Tube (QFT-GIT) test were performed in 214 contacts with normal chest radiographs. Rifampicin prophylaxis was initiated in TST+/QFT-GIT+ subjects, and the QFT-GIT test was repeated upon completion of 4 months of rifampicin treatment. Among the 214 contacts, the TST and QFT-GIT test results were positive in 67.7% and 56.7%, respectively, and the agreement between the two tests was fair-to-good (78.3%, kappa=0.55, p<0.001). The QFT-GIT test was positive in 77% (97/126) of contacts with positive TST results. Rifampicin prophylaxis was completed in 81 subjects with good compliance. Among 74 subjects with valid serial QFT-GIT test results, IFN-gamma levels decreased in 97.3% (72/74) of the subjects and QFT-GIT test reversion (positive to negative) was achieved in 31 subjects (41.9%). Subjects without QFT-GIT test reversion had a significantly higher baseline TST induration sizes (18.3+/-4.8 vs. 14.9+/-3.4mm, p<0.01) and IFN-gamma levels (18.6+/-17.9 vs. 3.2+/-7.5IU/mL, p<0.01) than the subjects with QFT-GIT test reversion. Thus, IGRAs may be useful in evaluating the therapeutic response to rifampicin prophylaxis in TB contacts. However, considering that this was not a controlled study, a prospective controlled study is needed to determine whether rifampicin prophylaxis truly affects QFT-GIT reversion.

Double-blind, randomized, placebo-controlled Phase I Clinical Trial of the therapeutical antituberculous vaccine RUTI

A Phase I interventional Clinical Trial was performed with a potential tuberculosis vaccine, based on detoxified cellular fragments of M. tuberculosis, named RUTI. The objective was to evaluate the safety profile and T-cell immune responses over a 6-month period following subcutaneous inoculation. The double-blind, randomized and placebo-controlled trial was conducted in healthy volunteers, all recruited at one site. RUTI, at each of the four tested doses, starting from 5microg and going up to 200microg, and placebo were inoculated to groups of 4 and 2 volunteers respectively, consecutively. RUTI appeared to be well tolerated as judged by local and systemic clinical evaluation, though vaccine dose dependent local adverse reactions were recorded. T-cell responses of blood lymphocytes to PPD and a number of antigen subunits were elevated, when compared with controls subjects. These results support the feasibility of future evaluation, to be targeted at subjects with latent tuberculosis infection (LTBI).

[Difficulties of TB diagnosis in children: QuantiFERON TB Gold In-Tube as useful tool]

Diagnosis of childhood tuberculosis (TB), active TB or latent tuberculosis infection (LTBI), is complicated by uncommon clinical, radiological and bacteriological features. The tuberculin skin test (TST) is imperfect: difficulty of the intradermal injection for the child, lack of sensibility and specificity. The stop of the systematic inoculation by the BCG since July 2007, in France, could lead to an increase of the incidence of the childhood TB. It is urgent to find new diagnostic tools: sensitive, specific, fast, of objective reading and little expensive. Interferon-gamma assays could be useful but the data are still insufficient in paediatrics and sometimes contradictory. A prospective study which compared the usefulness of QuantiFERON TB Gold In-Tube (QFT-IT) assay with TST to detect LTBI or active disease in 51 children was realised in University Hospital of Nancy. This allowed us to confirm interest of QFT-IT; however, surprisingly, very discordant QFT-IT and TST results were obtained (only five children were QFT-IT+/TST+). A high number (14%) of indeterminate QFT-IT occurred, without explanation by pre-analytical or clinical parameters. Further studies are needed to demonstrate the usefulness of this assay in diagnosing LTBI and particularly active TB in children.

Variation in T-SPOT.TB spot interpretation between independent observers from different laboratories

T-SPOT.TB is a specific assay for the diagnosis of tuberculosis. The assay needs to be performed with freshly isolated cells, and interpretation requires training. T-SPOT.TB has been used in various clinical-epidemiological settings, but so far no studies have evaluated the effect of interobserver variation in test reading. Our aim was to evaluate variation between different observers in reading T-SPOT.TB results. The study was nested within an ongoing cohort study, in which part of the T-SPOT.TB had been performed with frozen material. Culture plates were read visually by four different observers from two laboratories and by two automated readers. Of 313 T-SPOT.TB assays, 235 were performed with fresh cells and 78 were performed with frozen cells. No significant difference was found between results obtained with fresh cells and those obtained with frozen cells. The percentage of positive results varied between readers by maximally 15%; five/six raters were within a 6% difference in positive results. Analysis of the observed interrater differences showed that some individuals systematically counted more spots than others did. Because test interpretation includes subtraction of background values, this systematic variance had little influence on interindividual differences. The test result as positive or negative varied between independent raters, mainly due to samples with values around the cutoff. This warrants further study regarding determinants affecting the reading of T-SPOT.TB.

T-cell-based diagnosis of tuberculosis infection in children in Lithuania: a country of high incidence despite a high coverage with bacille Calmette-Guerin vaccination

Background

Lithuania is a country with a high incidence of tuberculosis (TB), despite a high coverage with bacille Calmette-Guerin (BCG) vaccination. Until now the only method used to detect latent TB infection was the tuberculin skin test (TST). However, TST may have a cross reactivity to the BCG vaccine and to environmental mycobacteria. The aim of this study was to conduct assessments of the diagnostic accuracy of the T-cell based test (T SPOT TB) for TB in children who had previously been BCG vaccinated and compare these with the results of the TST.

Methods

Between January 2005 and February 2007, children with bacteriologically confirmed TB, children having contacts with a case of infectious pulmonary TB and children without any known risk for TB were tested with both the TST and T SPOT TB.

Results

The TST and T SPOT TB tests were positive for all patients in the „culture-confirmed TB“ group. Whereas, in the „high risk for TB“ group, the TST was positive for 60%, but the T SPOT TB test, only for 17.8%. Meanwhile the results for the „low risk for TB“ group were 65.4% and 9.6%, respectively. A correlation between the TST and T SPOT TB was obtained in the "culture-confirmed TB" group where the TST ≥15 mm (r = 0.35, p < 0.001).

Conclusion

The T-cell based method is more objective than the TST for identifying latent TB infection in children who had been previously BCG vaccinated. This method could be useful in countries like Lithuania where there is a high incidence of TB despite a high coverage with BCG vaccination. It may also help to avoid unnecessary chemoprophylaxis when TST reactions are false-positive.

T-cell interferon-gamma release assays for the rapid immunodiagnosis of tuberculosis: clinical utility in high-burden vs. low-burden settings

PURPOSE OF REVIEW

The utility of T-cell interferon-gamma (IFN-gamma) responses to Mycobacterium tuberculosis specific antigens [interferon-gamma release assays (IGRAs)] in high-burden settings remains unclear and there is growing evidence that IGRA performance varies across high tuberculosis (TB) burden vs. low TB burden settings. Here we review the evidence supporting the utility of IGRAs in specific subgroups and compare their performance in high-burden vs. low-burden settings.

RECENT FINDINGS

Although the IGRA, compared with the tuberculin skin test (TST), has greater specificity in BCG-vaccinated individuals, treatment of latent tuberculosis infection is not a priority in high-burden setting. Nevertheless, in high-burden settings, the TST performs reasonably well and correlates as well, or better, with proxy measures of exposure.

SUMMARY

IGRAs may still be useful in high-burden settings in specific subgroups at high risk of progression, including young children, HIV-infected individuals and healthcare workers, but this requires confirmation. Although the IGRAs cannot distinguish between latent and active TB, their utility as rule-out tests, when combined with smear microscopy or the TST, requires further study. Prospective studies are required in high-burden settings to confirm whether IFN-gamma responses are predictive of high risk of progression to active TB, particularly in HIV-infected individuals.

In-hospital contact investigation among health care workers after exposure to smear-negative tuberculosis

Background

Smear-negative pulmonary tuberculosis (TB) accounts for a considerable proportion of TB transmission, which especially endangers health care workers (HCW). Novel Mycobacterium-tuberculosis-specific interferon-γ release assays (IGRAs) may offer the chance to define the burden of TB in HCW more accurately than the Mantoux tuberculin skin test (TST), but the data that is available regarding their performance in tracing smear-negative TB in the low-incidence, in-hospital setting, is limited. We conducted a large-scale, in-hospital contact investigation among HCW of a German university hospital after exposure to a single case of extensive smear-negative, culture-positive TB with pulmonary involvement. The objective of the present study was to evaluate an IGRA in comparison to the TST and to identify risk factors for test positivity.

Methods

Contacts were prospectively enrolled, evaluated using a standardized questionnaire, the IGRA QuantiFERON^®-TB Gold in Tube (QFT-GIT) and the TST, and followed-up for two years. Active TB was ruled out by chest x-ray in QFT-GIT-positive subjects. Independent predictors of test positivity were established through the use of logistic regression analysis.

Results

Out of the 143 subjects analyzed, 82 (57.3%) had close contact, but only four (2.8%) experienced cumulative exposure to the index case >40 hours. QFT-GIT results were positive in 13 subjects (9.1%), while TST results were positive in 40 subjects (28.0%) at an induration >5 mm. Overall agreement was poor between both tests (kappa = 0.15). Age was the only predictor of QFT-GIT-positivity (Odds ratio 2.7, 95% confidence interval 1.32–5.46), while TST-positivity was significantly related to Bacillus Calmette-Guérin vaccination and foreign origin. Logistic regression analysis showed no relation between test results and exposure. No secondary cases of active TB were detected over an observational period of two years.

Conclusion

Our findings suggest a low contagiosity of the particular index case. The frequency of positive QFT-GIT results may in fact reflect the pre-existing prevalence of latent TB infection among the study population. TB transmission seems unlikely and contact tracing not generally warranted after cumulative exposure <40 hours. However, the substantially lower frequency of positive QFT-GIT results compared to the TST may contribute to enhanced TB control in health care.

In vivo and in vitro effects of antituberculosis treatment on mycobacterial interferon-gamma T cell response

Background

In recent years, the impact of antituberculous treatment on interferon (IFN)-γ response to Mycobacterium tuberculosis antigens has been widely investigated, but the results have been controversial. The objective of the present study was: i) to evaluate longitudinal changes of IFN-γ response to M. tuberculosis-specific antigens in TB patients during antituberculous treatment by using the QuantiFERON-TB Gold (QFT-G) assay; ii) to compare the differences in T-cell response after a short or prolonged period of stimulation with mycobacterial antigens; iii) to assess the CD4+ and CD8+ T cells with effector/memory and central/memory phenotype; iv) to investigate the direct in vitro effects of antituberculous drugs on the secretion of IFN-γ.

Principal Findings

38 TB patients was evaluated at baseline and at month 2 and 4 of treatment and at month 6 (treatment completion). 27 (71%) patients had a QFT-G reversion (positive to negative) at the end of therapy, while 11 (29%) TB patients remained QFT-G positive at the end of therapy. Among the 11 patients with persistent positive QFT-G results, six had a complete response to the treatment, while the remaining 5 patients did not have a resolution of the disease. All 27 patients who became QFT-G negative had a complete clinical and microbiological recovery of the TB disease. In these patients the release of IFN-γ is absent even after a prolonged 6-day incubation with both ESAT-6 and CFP-10 antigens and the percentage of effector/memory T-cells phenotype was markedly lower than subjects with persistent positive QFT-G results. The in vitro study showed that antituberculous drugs did not exert any inhibitory effect on IFN-γ production within the range of therapeutically achievable concentrations.

Conclusions

The present study suggests that the decrease in the M. tuberculosis-specific T cells responses following successful anti-TB therapy may have a clinical value as a supplemental tool for the monitoring of the efficacy of pharmacologic intervention for active TB. In addition, the antituberculous drugs do not have any direct down-regulatory effect on the specific IFN-γ response.

New diagnostic methods for tuberculosis

PURPOSE OF REVIEW

During the last decade, laboratory tests for the detection of Mycobacterium tuberculosis (Mtb) have improved dramatically. Improvements in the ability to detect latent infection with Mtb, disease associated with Mtb, and strains resistant to commonly used antibiotics are reviewed.

RECENT FINDINGS

Advances in the detection of Mtb include light-emitting diode fluorescence microscopy, nucleic acid amplification of Mtb and drug-resistant strains, and more rapid liquid culture with adjunct drug susceptibility testing. In the detection of latent tuberculosis infection, interferon [gamma] release assays offer improved accuracy over the tuberculin skin test.

SUMMARY

The past 10 years have seen the most rapid growth in new diagnostics for Mtb in over a century. Although these tests offer improvements in the ability to detect Mtb, drug-resistant isolates, and those with latent tuberculosis infection, these improvements are counter-balanced by the need to deploy these tests in areas where Mtb burden is highest.

Use of T cell-based diagnosis of tuberculosis infection to optimize interpretation of tuberculin skin testing for child tuberculosis contacts

BACKGROUND

Treatment of recent tuberculosis infection in children aged <2 years is essential, because of high risk of progression to disease, but diagnosis is hindered by the inaccuracy of the tuberculin skin test (TST). More-accurate T cell-based tests of infection could enhance diagnosis by optimizing interpretation of the TST results.

METHODS

A total of 979 child tuberculosis contacts in Istanbul underwent the TST and enzyme-linked immunospot assay. Using enzyme-linked immunospot test results as a reference standard, we assessed the effect of age and bacille Calmette-Guérin (BCG) vaccination on the sensitivity and specificity of the TST, and we computed the optimal TST cutoff points, using receiver operating characteristic curves.

RESULTS

With a TST cutoff point of >or=10 mm, the sensitivity of the TST was 66% for children aged <2 years, which was lower than that for older children (P= .006). Specificity was 75% for BCG-vaccinated children, compared with 92% for unvaccinated children (P= .001). Optimal cutoff points improved TST specificity for children with 1 BCG scar, with little loss of sensitivity. Despite the use of optimal cutoff points, TST sensitivity remained <70% for children aged <2 years, specificity remained <87% for BCG-vaccinated children aged >or=2 years, and overall accuracy was low for children with >1 BCG scar.

CONCLUSIONS

Negative results of the TST cannot exclude tuberculosis infection for child tuberculosis contacts aged <2 years, which supports the use of preventive therapy regardless of the TST results for this age group. In children aged >or=2 years, the accuracy of the TST can be improved by adjustment of cutoff points for BCG-vaccinated children but remains poor for children with >1 BCG scar. This methodology can define optimal TST cutoff points for diagnosis of tuberculosis infection tailored to target populations.

IGRA tests perform similarly to TST but cause no adverse reactions: pediatric experience in Finland

Background

Two commercial interferon gamma release assays (IGRAs) (QuantiFERON^®-TB Gold in Tube and T SPOT^®-TB) to detect a contact with M. tuberculosis have recently become available. The majority of studies agree that the sensitivity and specificity of these methods are superior to the Tuberculin Skin Tests (TSTs) in detecting an exposure to bacteria in latently infected individuals and in clinical tuberculosis. However, the data in children remains limited.

Findings

Consecutively collected samples from children (n = 99) representing age range from zero to 18 years were analyzed in a retrospective non-blinded study. The two IGRAs were modified and adapted to the needs of Finland, a country of a low tuberculosis incidence. For 27 children, both tests were performed simultaneously and compared with the TST and clinician's diagnosis. The sensitivity, specificity, and accuracy of both IGRAs was determined. QuantiFERON TB Gold and T SPOT-TB performed (respectively) as follows: sensitivities 0.92 (95% confidence interval, CI, 0.67–0.99) and 0.85 (0.64–0.95); specificities 0.91 (0.77–0.97) and 1.00 (0.93–1.00); accuracies 0.91 (0.80–0.97) and 0.96 (0.88–0.99). This compares favorably to the TST whose known figures are 0.90, 0.95, and 0.95, respectively. The agreement between the IGRAs was high, k = 0.89. Finally, both methods agreed well with the TST, k = 0.86 for TST/QuantiFERON-TB Gold and k = 0.76 for TST/T SPOT-TB.

Conclusion

The sensitivity and specificity of IGRA methods compares well with the TST without the inconveniences and complications associated with TST, including exaggerated delayed type hypersensitivity reactions. These properties place them as acceptable substitutes for TST.

Latent tuberculosis diagnosis in children by using the QuantiFERON-TB Gold In-Tube test

BACKGROUND

The QuantiFERON-TB Gold test was the first blood test to be approved for the diagnosis of latent tuberculosis infection. Although it has been shown to be sensitive and specific in adults, limited data on its performance in children are available.

METHODS

This was a prospective study of children receiving health care in New York, New York. Each child was assessed for risk factors for Mycobacterium tuberculosis infection, underwent tuberculin skin testing, and had a QuantiFERON-TB Gold In-Tube test performed. The concordance between tuberculin skin test and QuantiFERON-TB Gold In-Tube test results was calculated, and the results were analyzed according to the likelihood of exposure to M tuberculosis.

RESULTS

Data for 207 children with valid tuberculin skin test and QuantiFERON-TB Gold In-Tube test results were analyzed. There was excellent correlation between negative tuberculin skin test results and negative QuantiFERON-TB Gold In-Tube test results; however, only 23% of children with positive tuberculin skin test results had positive QuantiFERON-TB Gold In-Tube test results. Positive QuantiFERON-TB Gold In-Tube test results were associated with increased likelihood of M tuberculosis exposure, and interferon gamma levels were higher in children with known recent exposure to M tuberculosis, compared with children with older exposure histories. Younger children produced lower interferon gamma levels in response to the mitogen (phytohemagglutinin) control used in the QuantiFERON-TB Gold In-Tube test, but indeterminant results were low for children of all ages. Performance characteristics were similar across all age groups.

CONCLUSION

The QuantiFERON-TB Gold In-Tube test is a specific test for M tuberculosis exposure in children, with performance characteristics similar to those for adults residing in regions with low levels of endemic disease. Concerns about test sensitivity, especially for children <2 years of age, will require additional prospective long-term evaluation.

Clinical evaluation of the T-SPOT.TB test for patients with indeterminate results on the QuantiFERON TB-2G test

OBJECTIVE

To evaluate the clinical utility of the T-SPOT.TB test for patients with indeterminate results on the QFT-2G test.

MATERIALS AND METHODS

Forty patients (10.6%) showed indeterminate results among 378 patients who underwent QFT-2G test because active TB disease was clinically suspected. T-SPOT.TB test was performed for these 40 patients before the initiation of antituberculous treatment.

RESULTS

Forty patients (10.6%) were judged as showing indeterminate results on QFT-2G test because the positive control presented a lower IFN-gamma level. Elderly patients (68.2 versus 57.7) or immunocompromised patients receiving immunosuppressive treatments and patients with a decrease in lymphocyte count, serum protein and albumin were more frequently recognized in the patients with indeterminate results compared to those with determinate results on QFT-2G test. T-SPOT.TB test could clearly demonstrate the results in 26 of the 40 patients (65.0%) with indeterminate results of QFT-2G test; these were divided into six patients with positive results and 20 with negative results of T-SPOT.TB test. Elderly patients (73.5 versus 64.3) or patients with underlying diseases such as malignant disease and those receiving immunosuppressive treatment and patients with hyponutritional conditions were more frequently recognized in the patients with indeterminate results compared to patients with determinate results on both tests.

CONCLUSION

We think it may be necessary to introduce T-SPOT.TB test to increase the diagnostic rate of TB disease including latent tuberculosis infection because indeterminate results of QFT-2G test might be further decreased using T-SPOT.TB test. Although 14 patients showed indeterminate results on both tests, the lymphocytes of these patients may not possess functional cytokine production activity.

Quantitative T-cell interferon-gamma responses to Mycobacterium tuberculosis-specific antigens in active and latent tuberculosis

The objective was to compare the quantitative T-cell responses measured by the commercial interferon-gamma (IFNgamma) release assays (IGRAs) in active and latent tuberculosis (TB) states. T-cell responses of culture-proven TB cases were compared with those of contacts with positive IGRA results and tuberculin skin tests >or= 15 mm. T-SPOT.TB results in 270 active TB cases and 183 community contacts showed the median spot-forming cells (SFCs) above negative control/2.5 x 10(5) peripheral blood mononuclear cells to be 27 (-1 to 203) vs 10 (-2 to 174) in response to ESAT-6 (p < 0.001); and 37 (0 to 293) vs 13 (0 to 225) to CFP-10 (p < 0.001). The median IFNgamma levels (antigen minus nil control) as measured by QuantiFERON-TB Gold In-tube in 270 cases and 142 contacts in congregate settings was 2.3 IU/ml (-0.58 to 31.44) vs 1.7 IU/ml (0.35 to 26.51, p = 0.98). Quantitative T-cell responses as measured by the T-SPOT.TB may indicate mycobacterial burden and disease activity, but cannot be used to discriminate active from latent TB.

Discordant QuantiFERON-TB Gold test results among US healthcare workers with increased risk of latent tuberculosis infection: a problem or solution?

OBJECTIVE

In late 2006, our hospital implemented use of the QuantiFERON-TB Gold (QFT-G) assay, a whole-blood interferon-gamma release assay, for detection of tuberculosis infection. All newly hired healthcare workers (HCWs) with positive Mantoux tuberculin skin test (TST) results were routinely tested with the QFT-G assay, to take advantage of its higher specificity. We then undertook a quality assurance review to evaluate the QFT-G test results in HCWs with multiple risk factors for latent tuberculosis infection (LTBI).

METHODS

The clinical records for TST-positive HCWs tested with the QFT-G assay were reviewed. HCWs with 2 or more risk factors commonly associated with LTBI were classified as "increased risk" (IR). IR HCWs who had negative QFT-G test results underwent repeat QFT-G testing and were offered testing with a different interferon-gamma release assay (T-SPOT.TB) and with extended T cell stimulation assays.

RESULTS

Of 143 TST-positive HCWs tested with the QFT-G assay, 26 (18%) had positive results, 115 (81%) had negative results, and 2 (1%) had indeterminate results. Of 82 IR HCWs, 23 (28%) had positive QFT-G test results, and 57 (70%) had negative results. Of the 57 IR HCWs with negative results, 43 underwent repeat QFT-G testing: 41 had negative results again, and 2 had positive results. These 43 HCWs were also offered additional testing with the T-SPOT.TB diagnostic, and 36 consented: 31/36 tested negative, and 5/36 tested positive. Extended assays using the antigens ESAT-6 and CFP-10 confirmed the positive results detected by the overnight assays and yielded positive results for an additional 7/36 (19%) of individuals; strikingly, all 36 HCWs had strongly positive test results with assays using purified protein derivative.

CONCLUSIONS

The extreme discordance between the results of our clinical diagnostic algorithm and the results of QFT-G testing raises concern about the sensitivity of the QFT-G assay for detection of LTBI in our HCWs. Results of extended stimulation assays suggest that many of our IR HCWs have indeed been sensitized to Mycobacterium tuberculosis. It is possible that the QFT-G assay identifies those at higher reactivation risk rather than all previously infected, but, in the absence of long-term follow-up data, we should interpret negative QFT-G results with some caution.

School based screening for tuberculosis infection in Norway: comparison of positive tuberculin skin test with interferon-gamma release assay

Background

In Norway, screening for tuberculosis infection by tuberculin skin test (TST) has been offered for several decades to all children in 9th grade of school, prior to BCG-vaccination. The incidence of tuberculosis in Norway is low and infection with M. tuberculosis is considered rare. QuantiFERON^®TB Gold (QFT) is a new and specific blood test for tuberculosis infection. So far, there have been few reports of QFT used in screening of predominantly unexposed, healthy, TST-positive children, including first and second generation immigrants. In order to evaluate the current TST screening and BCG-vaccination programme we aimed to (1) measure the prevalence of QFT positivity among TST positive children identified in the school based screening, and (2) measure the association between demographic and clinical risk factors for tuberculosis infection and QFT positivity.

Methods

This cross-sectional multi-centre study was conducted during the school year 2005–6 and the TST positive children were recruited from seven public hospitals covering rural and urban areas in Norway. Participation included a QFT test and a questionnaire regarding demographic and clinical risk factors for latent infection. All positive QFT results were confirmed by re-analysis of the same plasma sample. If the confirmatory test was negative the result was reported as non-conclusive and the participant was offered a new test.

Results

Among 511 TST positive children only 9% (44) had a confirmed positive QFT result. QFT positivity was associated with larger TST induration, origin outside Western countries and known exposure to tuberculosis. Most children (79%) had TST reactions in the range of 6–14 mm; 5% of these were QFT positive. Discrepant results between the tests were common even for TST reactions above 15 mm, as only 22 % had a positive QFT.

Conclusion

The results support the assumption that factors other than tuberculosis infection are widely contributing to positive TST results in this group and indicate the improved specificity of QFT for latent tuberculosis. Our study suggests a very low prevalence of latent tuberculosis infection among 9th grade school children in Norway. The result will inform the discussion in Norway of the usefulness of the current TST screening and BCG-policy.

Accuracy of immunodiagnostic tests for active tuberculosis using single and combined results: a multicenter TBNET-Study

Background

The clinical application of IFN-γ release assays (IGRAs) has recently improved the diagnosis of latent tuberculosis infection. In a multicenter study of the Tuberculosis Network European Trialsgroup (TBNET) we aimed to ascertain in routine clinical practice the accuracy of a novel assay using selected peptides encoded in the mycobacterial genomic region of difference (RD) 1 for the diagnosis of active tuberculosis in comparison with tuberculin skin test (TST), QuantiFERON-TB GOLD In-Tube (Cellestis Ltd., Carnegie, Australia) and T-SPOT.TB (Oxfordimmunotec, Abingdon, UK).

Principal Findings

425 individuals from 6 different European centres were prospectively enrolled. We found that sensitivity of the novel test, TST, QuantiFERON-TB GOLD In-Tube and T-SPOT.TB was respectively 73.1%, 85.3%, 78.1%, and 85.2%; specificity was respectively 70.6%, 48.0%, 61.9% and 44.3%; positive likelihood ratios were respectively 2.48, 1.64, 2.05, and 1.53; negative likelihood ratios were respectively 0.38, 0.31, 0.35, 0.33. Sensitivity of TST combined with the novel test, QuantiFERON-TB GOLD In-Tube and T-SPOT.TB increased up to 92.4%, 97.7% and 97.1%, respectively. The likelihood ratios of combined negative results of TST with, respectively, the novel test, QuantiFERON-TB GOLD In-Tube and T-SPOT.TB were 0.19, 0.07 and 0.10.

Conclusions

The assay based on RD1 selected peptides has similar accuracy for active tuberculosis compared with TST and commercial IGRAs. Then, independently of the spectrum of antigens used in the assays to elicit mycobacterial specific immune responses, the novel test, IGRAs, and the TST do not allow an accurate identification of active tuberculosis in clinical practice. However, the combined use of the novel assay or commercial IGRAs with TST may allow exclusion of tuberculosis.

Enhancement of human antigen-specific memory T-cell responses by interleukin-7 may improve accuracy in diagnosing tuberculosis

Children and immunocompromised adults are at an increased risk of tuberculosis (TB), but diagnosis is more challenging. Recently developed gamma interferon (IFN-gamma) release assays provide increased sensitivity and specificity for diagnosis of latent TB, but their use is not FDA approved in immunocompromised or pediatric populations. Both populations have reduced numbers of T cells, which are major producers of IFN-gamma. Interleukin 7 (IL-7), a survival cytokine, stabilizes IFN-gamma message and increases protein production. IL-7 was added to antigen-stimulated lymphocytes to improve IFN-gamma responses as measured by enzyme-linked immunosorbent assay (ELISA) and enzyme-linked immunospot (ELISPOT) assay. Antigens used were tetanus toxoid (n = 10), p24 (from human immunodeficiency virus [HIV], n = 9), and TB peptides (n = 15). Keyhole limpet hemocyanin was used as a negative control, and phytohemagglutinin was the positive control. IL-7 improved antigen-specific responses to all antigens tested including tetanus toxoid, HIV type 1 p24, and TB peptides (ESAT-6 and CFP-10) with up to a 14-fold increase (mean = 3.8), as measured by ELISA. Increased IFN-gamma responses from controls, HIV-positive patients, and TB patients were statistically significant, with P values of <0.05, 0.01, and 0.05, respectively. ELISPOT assay results confirmed ELISA findings (P values of <0.01, 0.02, and 0.03, respectively), with a strong correlation between the two tests (R(2) = 0.82 to 0.99). Based on average background levels, IL-7 increased detection of IFN-gamma by 39% compared to the level with antigen alone. Increased production of IFN-gamma induced by IL-7 improves sensitivity of ELISA and ELISPOT assays for all antigens tested. Further enhancement of IFN-gamma-based assays might improve TB diagnosis in those populations at highest risk for TB.

Paediatric tuberculosis

Tuberculosis continues to cause an unacceptably high toll of disease and death among children worldwide, particularly in the wake of the HIV epidemic. Increased international travel and immigration have led to a rise in childhood tuberculosis rates even in traditionally low burden, industrialised settings, and threaten to promote the emergence and spread of multidrug-resistant strains. Whereas intense scientific and clinical research efforts into novel diagnostic, therapeutic, and preventive interventions have focused on tuberculosis in adults, childhood tuberculosis has been relatively neglected. However, children are particularly vulnerable to severe disease and death following infection, and those with latent infection become the reservoir for future transmission following disease reactivation in adulthood, fuelling future epidemics. Further research into the epidemiology, immune mechanisms, diagnosis, treatment, and prevention of childhood tuberculosis is urgently needed. Advances in our understanding of tuberculosis in children would provide insights and opportunities to enhance efforts to control this disease.

A three-way comparison of tuberculin skin testing, QuantiFERON-TB gold and T-SPOT.TB in children

Background

There are limited data comparing the performance of the two commercially available interferon gamma (IFN-γ) release assays (IGRAs) for the diagnosis of tuberculosis (TB) in children. We compared QuantiFERON-TB gold In Tube (QFT-IT), T-SPOT.TB and the tuberculin skin test (TST) in children at risk for latent TB infection or TB disease.

Methods and Findings

The results of both IGRAs were compared with diagnosis assigned by TST-based criteria and assessed in relation to TB contact history. Results from the TST and at least one assay were available for 96 of 100 children. Agreement between QFT-IT and T-SPOT.TB was high (93% agreement, κ = 0.83). QFT-IT and T-SPOT.TB tests were positive in 8 (89%) and 9 (100%) children with suspected active TB disease. There was moderate agreement between TST and either QFT-IT (75%, κ = 0.50) or T-SPOT.TB (75%, κ = 0.51). Among 38 children with TST-defined latent TB infection, QFT-IT gold and T-SPOT.TB assays were positive in 47% and 39% respectively. Three TST-negative children were positive by at least one IGRA. Children with a TB contact were more likely than children without a TB contact to have a positive IGRA (QFT-IT LR 3.9; T-SPOT.TB LR 3.9) and a positive TST (LR 1.4). Multivariate linear regression analysis showed that the magnitude of both TST induration and IGRA IFN-γ responses was significantly influenced by TB contact history, but only the TST was influenced by age.

Conclusions

Although a high level of agreement between the IGRAs was observed, they are commonly discordant with the TST. The correct interpretation of a negative assay in a child with a positive skin test in clinical practice remains challenging and highlights the need for longitudinal studies to determine the negative predictive value of IGRAs.

Comparison of the interferon- gamma release assay and the tuberculin skin test for contact investigation of tuberculosis in BCG-vaccinated health care workers

Health care workers are at increased risk of Mycobacterium tuberculosis infection. The tuberculin skin test (TST) is frequently false positive in BCG-vaccinated health care workers. QuantiFERON-TB GOLD (QFT-G) is a sensitive and specific interferon-gamma release assay unaffected by BCG vaccination. This study compared TST and QFT-G in the diagnosis of latent TB infection in BCG-vaccinated health care workers. 39 health care workers exposed to a smear-positive TB patient were enrolled. Initial TST was positive in 33 (84.6%) cases, but only 4 (10.2%) cases using QFT-G. TST conversion occurred in 2/6 (33.3%), compared to 4/32(12.5%), cases using QFT-G. A higher proportion of QFT converters was associated with intimate contact, although not reaching statistical significance. Face-to-face contact >1 h was significantly associated with QFT-G conversion >or=0.7 IU/ml (OR 8.63, 95%CI 1.08-69.07, p=0.04). Agreement between TST and QFT-G was 18.0%, (kappa: -0.03). Concordance between TST and QFT (>or=0.35 IU/ml) conversion was 40.0%(kappa=-0.40), and 60.0%(kappa=0.00) if QFT >or=0.7 IU/ml was used. Agreement increased with increasing TST cut-offs. TST is not useful in contact investigation among BCG-vaccinated health care workers, in an area with intermediate burden of TB. QFT may provide additional information for the diagnosis and strategic management of preventive treatment of LTBI in BCG-vaccinated health care workers in a country with intermediate burden of TB.