Commercial Interferon-gamma Release Assays Research Articles

Evaluation of Diagnostic Performance of Three Commercial Interferon-Gamma Release Assays for Mycobacterium tuberculosis

Interferon-gamma release assays (IGRAs) have gained attention for the diagnosis of latent tuberculosis infection (LTBI) due to their higher specificity compared to the tuberculin skin test (TST). However, the IGRA’s performance varies across different populations. This study evaluated the diagnostic performance of three IGRAs (TBF-FIA, TBF-ELISA, and QFT-Plus) in Ghana, comparing them among individuals exposed and unexposed to MTB infection. Conducted in TB clinics across three regions, this prospective and cross-sectional study included healthy individuals with no known TB exposure (unexposed group) and patients with confirmed active TB (exposed group). Blood samples were tested using all three assays as per the manufacturers’ guidelines. The TBF-ELISA showed 3.4% higher sensitivity but 4.6% lower specificity compared to QFT-Plus. The TBF-FIA had sensitivity of 78.5–87.3% and specificity of 82.9–90.0%. These findings indicate that while the three IGRAs offer similar diagnostic accuracy, the variations in specificity and limited data on assays like TBF-FIA require further investigation.

Novel T cell interferon gamma release assay (IGRA) using spike recombinant protein for COVID19 vaccine response and Nucleocapsid for SARS-Cov2 response

We explored the performance of a whole blood interferon gamma release assay (IGRA) based on the stimulation of SARS-Cov2-specific T cells by purified recombinant proteins. Twenty volunteers vaccinated with BNT162b2 were selected first for T cell response evaluation using an in-house IGRA, a commercial IGRA, and ELISpot showing a S2 > S1 poly-epitopic response. Next, 64 vaccinated and 103 non-vaccinated individuals were tested for humoral and T cell response (IGRA-Spike/−nucleocapsid recombinant proteins). Following the second vaccine injection, humoral (100%) and IGRA-Spike T cell (95.3%) responses took place irrespective of sex, age, and vaccine type. The humoral response declined first, followed by IGRA-Spike T cell response after the second vaccine injection. Altogether, this study confirms the utility of the IGRA-Spike/−nucleocapsid assay to complement serology in COVID19 vaccinated individuals and those who have recovered from SARS-Cov2.

Commercial Interferon-gamma release assay to assess the immune response to first and second doses of mRNA vaccine in previously COVID-19 infected versus uninfected individuals

We analysed immunological response during vaccination by using quantitative anti-spike IgG antibodies (qAbs) and Interferon-gamma (IFNγ) production by SARS-CoV-2-specific CD4+ and CD8+ T cells (QuantiFERON® assay). Blood samples were collected at four time points: a day before the reception of first (T0) and second (T1) BNT162b2 doses, 14 (T2) and 28 days (T3) after second dose. Fifty individuals were included: 34 previously infected by SARS-CoV-2 (CoV2+) and 16 that were not (CoV2-). Among CoV2+, we only observed significant differences after the first dose in both qAbs and IFNγ+ T cells. CoV2- showed differences after each dose, and the response was lower than CoV2+. Older people presented a higher response in CoV2+, while in CoV2, young people responded best. Our results suggest that the second BNT162b2 vaccine dose is not a priority in people with previous COVID-19. QuantiFERON® is a good option to monitor T-cell immunity to SARS-CoV-2.

AB021. Comparing the performance of two interferon-gamma release assays in autoimmune skin disease patients: a prospective study

Autoimmune skin disease patients are standardly screened for tuberculosis (TB) via interferon-gamma release assays (IGRAs) prior to starting immunosuppressive drugs or enrolling in clinical trials. Two commercial IGRAs, T-SPOT.TB (T-SPOT) and QuantiFERON-Tb Gold (QFT-G), are reported as either determinate (positive or negative) or indeterminate. Both tests utilize similar immunoenzymatic reactions for interferon-gamma detection, but differ in quantification. Though QFT-G is more widely used, studies have demonstrated that T-SPOT has lower rates of indeterminate results in immunosuppressed patients. The newest generation of QFT-G, QuantiFERON-TB Gold Plus (QFT-Plus), has not been compared to T-SPOT in this patient population. We aim to investigate the performance of T-SPOT and QFT-Plus in autoimmune skin disease patients. This prospective study included 48 patients. Venous blood samples were collected and underwent TB screening with QFT-Plus and T-SPOT IGRAs. The proportions of indeterminate and determinate results among the two tests were compared. There were 2 indeterminate results with QFT-Plus and no indeterminate results with T-SPOT. There was one positive result for QFT-Plus and T-SPOT. Using a one-tailed Fischer test, there was no statistical significance when comparing QFT-Plus and T-SPOT in autoimmune skin disease patients (P=0.25). Although not statistically significant, it is clinically important as indeterminate results preclude these patients from receiving necessary treatment. Compared to previous studies on QFT-G, QFT-Plus showed improvement in reducing the amount of indeterminate results. We suggest using T-SPOT in TB screening for autoimmune skin disease patients who have an indeterminate QFT-G or QFT-Plus, as this test did not display any indeterminate results.

Detection of <i>M. tuberculosis</i> DNA in CD34-Positive Peripheral Blood Mononuclear Cells of Asymptomatic TB Contacts

Background: Haematopoietic stem cells expressing the CD34 surface marker have been posited as a niche for M. tuberculosis complex (MTBC) bacilli during latent tuberculosis infection (LTBI). Methods: We conducted a cross-sectional study in Ethiopia to determine whether MTBC DNA was detectable in peripheral blood mononuclear cells (PBMC) isolated from 100 ml blood taken from 197 asymptomatic adults with a history of recent household TB contact and/or HIV infection, using digital polymerase chain reaction (dPCR). A nested prospective study was conducted in a sub-set of 43 HIV-infected individuals to evaluate whether administration of isoniazid preventive therapy (IPT) was effective in clearing MTBC DNA from PBMC. Results: MTBC DNA was detected in PBMC of 156/197 participants (79.2%; 95% CI 73.5% to 84.9%). Where present, it was found more frequently in CD34-positive vs. CD34-negative PBMC (154/155 [99.4%] vs. 46/155 [29.7%], P<0.001). Prevalence of dPCR-detected MTBC DNA did not differ between QuantiFERON-negative vs. QuantiFERON-positive participants (77/99 [77.8%] vs. 79/98 [80.6%], P=0.73), but it was higher in HIV-infected vs. HIV-uninfected participants (67/75 [89.3%] vs. 89/122 [73.0%], P=0.006). By contrast, the proportion of QuantiFERON-positive participants was lower in HIV-infected vs. HIV-uninfected participants (25/75 [33.3%] vs. 73/122 [59.8%], P<0.001). Administration of IPT reduced prevalence of dPCR-detected MTBC DNA from 41/43 (95.3%) at baseline to 23/43 (53.5%) post-treatment (P<0.001), but it did not influence prevalence of QuantiFERON-positivity (17/43 [39.5%] at baseline vs. 13/43 [30.2%] post-treatment; P=0.13). Conclusions: We report a novel molecular microbiological biomarker of LTBI with properties that are distinct from those of a commercial interferon-gamma release assay. Our findings implicate the bone marrow as a niche for M. tuberculosis in latently infected individuals. Detection of MTBC DNA in PBMC has potential applications in the diagnosis of LTBI, in monitoring response to chemoprophylaxis and as an outcome measure in clinical trials of interventions to prevent or treat LTBI. Funding Statement: This work was supported by a grant from the United Kingdom Medical Research Council (Reference Number MR/P024548/1, to ARM). SF and STR acknowledge support from the Cambridge NIMR BRC antibiotic resistance theme. JM acknowledges support from the DELTAS Africa Initiative (ref DEL-15-011, via THRiVE-2). JFH, GJ and DMO’S acknowledge support from the UK government Department for Business, Energy & Industrial Strategy (BEIS). Declaration of Interests: STR has a pending patent that is relevant to the work. All other authors have no competing interests to declare. Ethics Approval Statement: The study was approved by the Ethiopian National Research Ethics Review Committee, Addis Ababa, Ethiopia (ref 310/253/2017). Written informed consent was obtained from all participants.

Can Interferon-γ Release Assays Be Useful for Monitoring the Response to Anti-tuberculosis Treatment?: A Systematic Review and Meta-analysis.

The number of studies which evaluated interferon-gamma release assays (IGRAs) results after anti-tuberculosis (TB) treatment has been rapidly increasing. The aim of this study was to investigate the potential use of IGRAs (QFT-GIT, T-SPOT.TB, QFT-Plus) in assessing the response to anti-TB treatment. We searched all studies in English language published from 1 October 2011 to 18 November 2018 in PubMed, Web of Science, and Scopus. Our search included the term "tuberculosis treatment AND interferon-γ release assay". We included studies evaluating the performance of commercial IGRAs (including QFT-GIT, T-SPOT.TB and QFT-Plus) before and after the anti-TB treatment. We performed subgroup analysis based on the age (children, adults), type of TB (active, latent, active and latent, and contacts exposed to MDR defined as MDR LTBI), type of IGRAs (QFT-GIT and T-SPOT.TB), and follow-up interval (2, 3, 4, 6, 9months). Of the 18 included studies, 12 used QFT-GIT for assessment of IGRA performance after therapy, 1 used T-SPOT.TB, and 3 used both QFT-GIT and T-SPOT.TB. Since then, only two studies have assessed the QFT-Plus performance during therapy. According to the results of the meta-analysis, the pooled rate of positive IGRAs (QFT-GIT and T-SPOT.TB) following anti-TB therapy was estimated at 76% [95% CI 70-81%] and no difference was found compared to the pooled positive rate of IGRAs before initiation of therapy which was 76% [95% CI 60-89%]. The subgroup analysis showed that the pooled rate of positive IGRAs (QFT-GIT and T-SPOT.TB) after anti-TB therapy was significantly higher in monitoring active TB subjects [80% (95% CI 74-88%)] than LTBI [71% (95% CI 70-81%)]. Available data are now sufficient to suggest that monitoring changes in the IGRAs (QFT-GIT and T-SPOT.TB) response during anti-TB treatment may have limited use in evaluating the effectiveness of treatment, while the monitoring changes in QFT-Plus during anti-tubercular treatment are recommended to determine treatment efficacy or for treatment monitoring. Further research is needed to establish the efficacy of this new assay as marker on a larger scale for treatment monitoring.

1390. A Novel Application of the Interferon-Gamma Release Assay (IGRA) Among End-Stage Heart Failure Patients Awaiting Heart Transplantation

BackgroundThe optimal approach to assay the immune status in heart failure is challenging because of the inherent complexity of chronic inflammation. Interferon-gamma release assays (IGRAs) measure an aspect of cell-mediated immunity encompassing both the innate and adaptive immunity. In this study, we evaluated the utility of a commercial IGRA for predicting mortality and infectious complications among heart transplant candidates.MethodsThis prospective cohort study was conducted between August 1, 2014 and January 31, 2019 at a medical center in Taiwan. All heart transplant candidates received an IGRA (QuantiFERON®-TB Gold In-Tube, QFT-GIT) at baseline as part of the initiative to screen for latent tuberculosis. Impaired cell-mediated immunity was defined as the release of <1 IU/mL of interferon-γ (IFN-γ) in response to the common mitogen in the positive control tube.The patients were then followed until death or January 31, 2019.ResultsA total of 102 patients were enrolled; of whom, 23 (22.5%) had impaired cell-mediated immunity at baseline. During the study period with a median follow-up of 1.90 years (IQR 1.17–3.56), 23 (22.5%) patients died and 45 (44.1%) patients developed an infectious complication. Overall mortality was significantly greater among those with impaired cell-mediated immunity [39.1% (9/23) vs. 17.7% (14/79), P = 0.031]. A trend toward higher rates of infection was observed among impaired cell-mediated immunity group [60.9% (14/23) vs. 39.2% (31/79), P = 0.066]. The most common cause of death was infection (56.5%). No patient developed active tuberculosis during the study and the most common infection was bacteremia (35.6%). In the age-adjusted multivariate analysis, impaired cell-mediated immunity was an independent predictor of mortality (HR 2.87, CI 1.23–6.68, P = 0.014) and subsequent infectious event (HR 3.00, CI 1.56–5.76, P = 0.001).ConclusionAn interferon-γ release assay utilizing the positive control tube of the QuantiFERON®-TB Gold In-Tube kit was predictive of overall mortality and infections among patients with advanced heart failure awaiting heart transplantation. Disclosures All authors: No reported disclosures.

571 Comparing the performance of two interferon-gamma release assays in autoimmune skin disease patients: A prospective study

Autoimmune skin disease patients are standardly screened for tuberculosis (TB) via interferon-gamma release assays (IGRAs) prior to starting immunosuppressive drugs or enrolling in clinical trials. Two commercial IGRAs, T-SPOT.TB and QuantiFERON-Tb Gold (QFT-G), are reported as either determinate (positive or negative) or indeterminate. Both tests utilize similar immunoenzymatic reactions for interferon-gamma detection, but differ in its quantification. Though QFT-G is more widely used, studies have demonstrated that T-SPOT.TB has lower rates of indeterminate results in immunosuppressed patients, and thus may prevent a delay in initiation of necessary therapies or enrollment in clinical trials. The newest generation of QFT-G, QuantiFERON-TB Gold Plus (QFT-Plus), has not been compared to T-SPOT.TB in this patient population. We aim to investigate the performance of T-SPOT.TB and QFT-Plus in autoimmune skin disease patients. This ongoing prospective study included 48 patients. Venous blood samples were collected and underwent TB screening with QFT-Plus and T-SPOT.TB IGRAs. The proportions of indeterminate and determinate results among the two tests were compared. There were 2 indeterminate results with QFT-Plus and no indeterminate results with T-SPOT.TB. There was one positive result seen with both QFT-Plus and T-SPOT.TB. Using a one-tailed Fischer test, there was no statistical significance when comparing QFT-Plus and T-SPOT.TB in autoimmune skin disease patients (p=0.25). Though this finding was not statistically significant, it is clinically important as indeterminate results preclude these patients from receiving necessary treatment. Compared to previous studies on QFT-G, QFT-Plus showed improvement in reducing the amount of indeterminate results. Despite this, we suggest using T-SPOT.TB in TB screening for autoimmune skin disease patients who have an indeterminate QFT-G or QFT-Plus, as this test did not display any indeterminate results. The results of this study are limited by small sample size.

A Novel Microfluidic Point-of-Care Biosensor System on Printed Circuit Board for Cytokine Detection.

Point of Care (PoC) diagnostics have been the subject of considerable research over the last few decades driven by the pressure to detect diseases quickly and effectively and reduce healthcare costs. Herein, we demonstrate a novel, fully integrated, microfluidic amperometric enzyme-linked immunosorbent assay (ELISA) prototype using a commercial interferon gamma release assay (IGRA) as a model antibody binding system. Microfluidic assay chemistry was engineered to take place on Au-plated electrodes within an assay cell on a printed circuit board (PCB)-based biosensor system. The assay cell is linked to an electrochemical reporter cell comprising microfluidic architecture, Au working and counter electrodes and a Ag/AgCl reference electrode, all manufactured exclusively via standard commercial PCB fabrication processes. Assay chemistry has been optimised for microfluidic diffusion kinetics to function under continual flow. We characterised the electrode integrity of the developed platforms with reference to biological sampling and buffer composition and subsequently we demonstrated concentration-dependent measurements of H2O2 depletion as resolved by existing FDA-validated ELISA kits. Finally, we validated the assay technology in both buffer and serum and demonstrate limits of detection comparable to high-end commercial systems with the addition of full microfluidic assay architecture capable of returning diagnostic analyses in approximately eight minutes.

Latent Tuberculosis Infection - Diagnosis and Treatment.

INTRODUCTION:Latent tuberculosis infection (LTBI) is defined as a state of persistent immune response to stimulation by Mycobacterium tuberculosis antigens without evidence of clinically manifested active tuberculosis (TB). Diagnosis and treatment for LTBI are important for TB, especially in high-risk populations. Tuberculin skin test (TST) and interferon-gamma release assays (IGRAs) are used to diagnose LTBI.AIM:The study aims to present the first results with IGRA test compared with TST in the screening of LTBI and the treatment results in the cases with LTBI in Macedonia.MATERIAL AND METHODS:In this study 73 cases diagnosed and treated with LTBI in 2016 were included. For diagnosis of LTBI, we used TST RT -23 5T.U. and commercial IGRA test such as QuantiFERON-TB Gold In-Tube (QFT-IT).RESULTS:Out of 73 cases with LTBI, 61.64% were men, and 38.36% were women. Among all age groups, the most frequent were cases between 5 and 14 years old (54.79%). Among the evaluated risk groups for LTBI, the most frequent were children household contacts with pulmonary TB cases (61-83.65%), followed by people living with HIV (9-12.33%) and only 3 cases with other medical reasons. Positive TST had 34 cases (46.57%) and positive IGRA test 25 cases (34.25%). Regarding the treatment regimes, we use two regimes: 50 cases (68.44%) received 6 months daily regime with Isoniazid, and 23 cases (31.51%) received 3 months daily regime with Isoniazid and Rifampicin. Treatment outcomes showed that the most patients completed treatment regimes: 55 (75.34%) and only 10 (13.09%) interrupted the treatment.CONCLUSION:Despite the progress made in the last few years, several challenges remain to be addressed for better management of LTBI which will contribute to strength TB control in the country.

The performance of T-cell Xtend reagent in increasing blood storage times for interferon gamma release assays.

T-cell Xtend (TCX) was introduced to extend the blood storage time for T-SPOT.TB test, a widely used commercial interferon gamma release assay (IGRA) for rapid in vitro tuberculosis. A total of 99 Uyghur suspected tuberculosis patients were recruited in this study. T-SPOT.TB test was performed with fresh blood (controls), 36hours delayed blood and delayed and TCX-treated (at 36hours) blood from each patient, respectively. White blood cells and lymphocytes proportion in peripheral blood mononuclear cells s and spot-forming cells in positive control wells decreased significantly in delayed blood samples when compared with controls, while this decrease was not detected in TCX-treated group. In the 58 patients with paired T-SPOT.TB results of three groups of samples, a higher positive rate was observed in TCX-treated group than both in controls and untreated group (41.4% vs 37.9% and 25.9%). The concordance of T-SPOT.TB results between the treated group and controls was 0.856, whereas the agreement between controls and untreated group was unsatisfactory (0.649). In the 23 elderly patients (>70 years old) with paired T-SPOT.TB results of controls and TCX group, treated group showed a non-significant trend toward higher positive rate than controls (43.5% vs 26.1%, P=.22). Meanwhile, TCX treatment reduced the risk of false negative T-SPOT.TB results in the elderly population. Deterioration of blood sample caused by long storage time can be neutralized by TCX treatment. The results provide data for the utility of TCX in a novel population and in Asian region, and reveal the potential of TCX to improve the accuracy of T-SPOT.TB test in elderly population.

Influence of the Spectrophotometer on Readings and Results Obtained from Commercial Equipment when using ELISA Post Interferon Gamma Release Assay for in vitro Diagnosis of Human Tuberculosis

Early and reliable laboratory diagnosis is very important to guide treatment of and control strategies for a disease. Some technical problems can occur due to laboratory facilities and methodological procedures. Many in vitro diagnoses are based on colorimetric methods such as the quantitative Enzyme- Linked Immuno Sorbent Assay (ELISA), whereby optical density (OD) is compared with a standard curve. The readings of these assays are based on absorption by a spectrophotometric device of light from a narrow or broad spectrum of waves. Objective: The aim of this work was to read the ELISA plate using different spectrophotometry equipment. Methods: Human plasma samples from healthy volunteers (n=50) and volunteers with tuberculosis (n=24) were prepared previously by whole blood incubation in the commercial Interferon Gamma Release Assay (IGRA) for in vitro diagnosis of tuberculosis and then the Interferon ELISA was performed using commercial equipment from the same manufacturer. The ELISA micro plates were read in three spectrophotometers with different filters/wavelengths: 450, 630 and 450 nm. The optical densities were established and analyzed using the manufacturer’s software program. The results of the readings performed at the recommended wavelength were compared with the other two filters/wavelengths. Results: Among the results obtained, 10 samples showed differences in the results of diagnosis. These discrepancies in metrology were associated with differences in the filters/wavelengths and were consequently identified as false results.

Management of latent Mycobacterium tuberculosis infection: WHO guidelines for low tuberculosis burden countries.

Latent tuberculosis infection (LTBI) is characterised by the presence of immune responses to previously acquired Mycobacterium tuberculosis infection without clinical evidence of active tuberculosis (TB). Here we report evidence-based guidelines from the World Health Organization for a public health approach to the management of LTBI in high risk individuals in countries with high or middle upper income and TB incidence of <100 per 100 000 per year. The guidelines strongly recommend systematic testing and treatment of LTBI in people living with HIV, adult and child contacts of pulmonary TB cases, patients initiating anti-tumour necrosis factor treatment, patients receiving dialysis, patients preparing for organ or haematological transplantation, and patients with silicosis. In prisoners, healthcare workers, immigrants from high TB burden countries, homeless persons and illicit drug users, systematic testing and treatment of LTBI is conditionally recommended, according to TB epidemiology and resource availability. Either commercial interferon-gamma release assays or Mantoux tuberculin skin testing could be used to test for LTBI. Chest radiography should be performed before LTBI treatment to rule out active TB disease. Recommended treatment regimens for LTBI include: 6 or 9 month isoniazid; 12 week rifapentine plus isoniazid; 3-4 month isoniazid plus rifampicin; or 3-4 month rifampicin alone.

Cross-sectional screening of healthcare workers at a regional chest clinic with an interferon gamma release assay: first report from Sri Lanka

Sri Lanka is a moderate burden middle-income setting where healthcare workers (HCWs) are not routinely screened for TB infection, even in moderate to high transmission risk settings. This study evaluated the use of a commercial interferon gamma release assay (IGRA) in HCW screening in comparison to the tuberculin skin test (TST) in a regional chest clinic. HCWs (n = 39) serving at the study clinic, where over 500 TB patients are registered and treated every year, were screened for LTBI with both the TST and an IGRA. Factors associated with positive test results as well as agreement between the two tests were evaluated. 47.2% of HCWs screened were TST positive (10mmcut-off) and positivity was associated with working in poorly ventilated areas (P = 0.019, OR 5.133 (95% CI 1.23 – 21.35)), although not associated with working in the sputum laboratory or TB treatment room, age or gender. IGRA positivity was significantly lower, 15.7%(P = 0.003). Positivity was associated with male gender (P = 0.046) and a shorter duration of service at the chest clinic (P = 0.036), though it was not associated with work in risk areas. Agreement between tests (TST 10mm cut-off) was fair with a kappa of 0.30 (P = 0.013). Positive IGRA results were seen only in TST-positive subjects who had a TST reading of >15mm. Occupational and non-occupational factors associated with TST and IGRA positivity differed between tests. Short duration of service was associated with IGRA positivity. The IGRA showed no advantage over the TST as a test for LTBI in this setting.

Do Anti-Tuberculous antibiotics or steroid therapy influence cytokine production in Quantiferon-TB gold in Tube-Based immunoassays?

The ability to monitor and confirm adequate treatment of latent tuberculosis (TB) infection would be a major advance. This would allow comparisons of antibiotic regimens and treatment durations, and help reduce transmission from subsequent reactivation following failed therapy. There has been recent interest in using commercial interferon-gamma release assays and other cytokine-based assays to monitor therapy. The potential immunomodulatory effects of therapeutic concentrations of anti-tuberculous drugs or steroids needs to be considered in assessing these assays for monitoring. We determined whether therapeutic concentrations of anti-tuberculous antibiotics or dexamethasone affect IFN-γ production in the QuantiFERON-TB-Gold In-Tube (QFT-IT) assay, as well as a range of other cytokines (TNF-α, IFN-γ, IL-lra, IL-2, IL-10, IL-13, IP-10, MIP-β). Blood was collected from ten adults with latent TB prior to starting preventive therapy. This was added to six sets of QFT-IT tubes containing therapeutic concentrations of isoniazid, rifampicin, isoniazid with rifampicin, ciprofloxacin, dexamethasone or nil. QFT-IT assays were then run according to manufacturer’s instructions. Remaining supernatant was used to measure the additional cytokines by Luminex assay. In four of ten participants the QFT-IT result changed from positive to negative as a result of incubation with antibiotics and/or dexamethasone. The greatest reduction in IFN-γ responses occurred with dexamethasone.

Frequent Detection of Latent Tuberculosis Infection among Aged Underground Hard Coal Miners in the Absence of Recent Tuberculosis Exposure

BackgroundMiners are at particular risk for tuberculosis (TB) infection due to exposure to silica dust and silicosis. The objectives of the present observational cohort study were to determine the prevalence of latent TB infection (LTBI) among aged German underground hard coal miners with silicosis or chronic obstructive pulmonary disease (COPD) using two commercial interferon-gamma release assays (IGRAs) and to compare their performance with respect to predictors of test positivity.MethodsBetween October 2008 and June 2010, miners were consecutively recruited when routinely attending pneumoconiosis clinics for an expert opinion. Both IGRAs, the QuantiFERON®-TB Gold In-Tube (QFT) and the T-SPOT®.TB (T-SPOT), were performed at baseline. A standardized clinical interview was conducted at baseline and at follow-up. The cohort was prospectively followed regarding the development of active TB for at least two years after inclusion of the last study subject. Independent predictors of IGRA positivity were calculated using logistic regression.ResultsAmong 118 subjects (mean age 75 years), none reported recent exposure to TB. Overall, the QFT and the T-SPOT yielded similarly high rates of positive results (QFT: 46.6%; 95% confidence interval 37.6–55.6%; T-SPOT: 61.0%; 95% confidence interval 52.2–69.8%). Positive results were independently predicted by age ≥80 years and foreign country of birth for both IGRAs. In addition, radiological evidence of prior healed TB increased the chance of a positive QFT result fivefold. While 28 subjects were lost to follow-up, no cases of active TB occurred among 90 subjects during an average follow-up of >2 years.ConclusionsConsidering the high prevalence of LTBI, the absence of recent TB exposure, and the currently low TB incidence in Germany, our study provides evidence for the persistence of specific interferon-gamma responses even decades after putative exposure. However, the clinical value of current IGRAs among our study population, although probably limited, remains uncertain.

P57 Comparative Cost-Effectiveness of IGRA to Detect Latent TB Infection in UK Inflammatory Bowel Disease Patients Initiating Anti-TNFα Agents

IntroductionTwo commercial Interferon Gamma release assays (IGRA) are approved in the UK by NICE to detect M tuberculosis (Mtb) infection. They use different test platforms. Both may provide borderline (neither...

Determining Mycobacterium tuberculosis Infection among BCG-Immunised Ugandan Children by T-SPOT.TB and Tuberculin Skin Testing

BackgroundChildren with latent tuberculosis infection (LTBI) represent a huge reservoir for future disease. We wished to determine Mycobacterium tuberculosis (M.tb) infection prevalence among BCG-immunised five-year-old children in Entebbe, Uganda, but there are limited data on the performance of immunoassays for diagnosis of tuberculosis infection in children in endemic settings. We therefore evaluated agreement between a commercial interferon gamma release assay (T-SPOT.TB) and the tuberculin skin test (TST; 2 units RT-23 tuberculin; positive defined as diameter ≥10 mm), along with the reproducibility of T-SPOT.TB on short-term follow-up, in this population.Methodology/Principal FindingsWe recruited 907 children of which 56 were household contacts of TB patients. They were tested with T-SPOT.TB at age five years and then re-examined with T-SPOT.TB (n = 405) and TST (n = 319) approximately three weeks later. The principal outcome measures were T-SPOT.TB and TST positivity. At five years, 88 (9.7%) children tested positive by T-SPOT.TB. More than half of those that were T-SPOT.TB positive at five years were negative at follow-up, whereas 96% of baseline negatives were consistently negative. We observed somewhat better agreement between initial and follow-up T-SPOT.TB results among household TB contacts (κ = 0.77) than among non-contacts (κ = 0.39). Agreement between T-SPOT.TB and TST was weak (κ = 0.28 and κ = 0.40 for T-SPOT.TB at 5 years and follow-up, respectively). Of 28 children who were positive on both T-SPOT.TB tests, 14 (50%) had a negative TST. Analysis of spot counts showed high levels of instability in responses between baseline and follow-up, indicating variability in circulating numbers of T cells specific for certain M.tb antigens.Conclusions/SignificanceWe found that T-SPOT.TB positives are unstable over a three-week follow-up interval, and that TST compares poorly with T-SPOT.TB, making the categorisation of children as TB-infected or TB-uninfected difficult. Existing tools for the diagnosis of TB infection are unsatisfactory in determining infection among children in this setting.

PTU-096 The use of commercial interferon-γ release assays to screen for mycobacterial infection in inflammatory bowel disease patients initiating anti-TNF agents

IntroductionTwo commercial Interferon Gamma release assays (IGRA) are approved in the UK by NICE and US FDA to detect M tuberculosis (Mtb) infection. The T-Spot.TB (TSTB) and Quanitferon Gold In-tube...

Interferon-gamma release assays for the tuberculosis serial testing of health care workers: a systematic review

BackgroundInterferon-gamma release assays (IGRAs) are increasingly used in the tuberculosis (TB) screening of health care workers (HCWs). However, comparatively high rates of conversions and reversion as well as growing evidence of substantial within-subject variability of interferon-gamma responses complicate their interpretation in the serial testing of HCWs.MethodsWe conducted a systematic review on the repeat use of the two commercial IGRAs, the QuantiFERON-TB Gold or In-Tube version (QFT) and the T-SPOT.TB (T-SPOT), in the serial testing and its with-subject variability among HCWs in order to provide guidance on how to interpret serial testing results in the context of the periodic screening of subjects with an increased occupational risk of latent TB infection (LTBI) in countries with low and intermediate TB incidence rates. The Medline, Embase, and Cochrane databases were searched without restrictions. Retrieved articles were complemented by additional hand searched records. Only studies that used commercial IGRAs among HCWs apart from contact and outbreak investigations and those fulfilling further predefined criteria were included.ResultsOverall, 20 studies, five using the T-SPOT and 19 using the QFT assay, were included. Fifteen studies met eligibility criteria for serial testing and five studies for within-subject variability. Irrespective of TB incidence rates in the study’s country of origin, reversion rates were consistently higher than conversion rates (range 22–71% vs. 1–14%). Subjects with baseline results around the diagnostic threshold were more likely to show inconsistent results on retesting. The within-subject variability of interferon-gamma responses was considerable across all studies systematically assessing it.ConclusionsOn the basis of reviewed studies we advocate using a borderline zone from 0.2–0.7 IU/ml for the interpretation of repeat QFT results in the routine screening of HCWs with an increased LTBI risk. Subjects with QFT results within this borderline zone, with suspected fresh infection, and those who are considered for preventive chemotherapy should be retested with the QFT within a period of about four weeks before preventive chemotherapy is recommended. However, the available data regarding the use of the T-SPOT in the serial testing of HCWs is remarkably limited and warrants further research.