A comparative study of two different methods for the detection of latent tuberculosis in HIV-positive individuals in Chile

Tuberculin skin test versus QuantiFERON-TB gold in-tube for latent tuberculosis screening in people living with HIV in a resource-limited setting

OBJECTIVE

To compare QuantiFERON-TB Gold-in-Tube (QFT) and tuberculin skin test (TST) in the diagnosis of latent tuberculosis infection (LTBI) among people living with HIV (PLWHIV).

METHODS

A cross-sectional study was carried out between 2017-2018. Tuberculin skin test and QFT were performed and their concordance was measured. The gold standard for LTBI was defined as positivity to any of the tests. A logistic regression model was carried out to predict the QFT result in patients with a negative TST.

RESULTS

A total of 510 PLWHIV were included, with 409 (80.2%) being male. The mean age of the patients was 41.3 ± 11.8 years. The median time since HIV diagnosis was 5 years (IQR 2-10), with a median CD4⁺ count of 541 (IQR 340-757) cells/mm³. Overall, 20 patients had an isolated TST+, 22 an isolated QFT+ and 15 had both positive. Concordance between tests showed a kappa coefficient of .37. Overcrowding was the only predictor for a positive QFT after a negative TST (p = .003).

CONCLUSION

There was fair agreement between tests in PLWHIV. In conditions of limited access to QTF, a TST-based strategy could be considered, with sequential use of QTF in high-risk patients with a negative result, especially those who live in overcrowded conditions.

Evaluation of role of interferon gamma release assays in the diagnosis of latent tuberculosis in human immunodeficiency virus-infected patients

Introduction:

Tuberculosis (TB) is the most common opportunistic infection in human immunodeficiency virus (HIV)-infected individuals. The risk of eventually developing active TB from latent TB infection (LTBI) is about 10% per year in HIV-positive patients in contrast to 10% lifetime risk in HIV-negative patients. Until recently, the tuberculin skin test (TST) was the only tool available for diagnosing LTBI. Interferon-gamma release assays (IGRAs) were recently developed and address many of the limitations of TST test, especially in immunocompromised state.

Aims and Objectives:

(1) To determine the prevalence of latent, active pulmonary, and multidrug-resistant (MDR)-TB among HIV-positive patients in and around Aligarh region; (2) sensitivity and specificity of TST and IGRAs for diagnosis of LTBI in HIV positive patients; and (3) to assess drug resistance and mutational patterns of the clinical isolates of MDR-TB in HIV-TB co-infection.

Materials and Methods:

A cross-sectional study was done on all the patients attended the ICTC centre, JNMC, AMU Aligarh, seropositive for HIV, i.e. 469 (sample size) for the study period of 2 years from October 2015 to October 2017. All 469 HIV-positive patients were screened for latent and active pulmonary TB. Diagnosis of TB (active and latent) was made using clinical, radiological, and microbiological tests. TST and IGRA testing along with CD4 cell counts were also determined. Line probe assay was also done to assess drug resistance and mutational patterns of MDR-TB in HIV patients.

Results:

In our study, prevalence of HIV infection was 5.04%. Sixty-seven (14.28%) patients were as active TB (HIV-TB co-infection), out of which only one patient (1.49%) was confirmed as MDR-TB, 117 (24.94%) were diagnosed as LTBI. It was also evaluated that IGRA has more sensitivity (75%) and specificity (76%) than TST with sensitivity of 71.7% and specificity 66%.

Conclusion:

As there is no gold standard test for latent TB, longitudinal follow-up is needed to interpret discordant test results. There is a need to interpret negative QFT results with caution and to test for latent TB at higher CD4 counts, if possible. Interferon gamma assays can become better tool for diagnosis of especially for latent TB. However, more research study required for establish their relevance, especially in immunocompromised states.

Caracterización de los pacientes menores de 15 años con tuberculosis en el Hospital Universitario San Vicente Fundación, 2011-2018

La Tuberculosis (TB) es la enfermedad infecciosa que más daño ha causado a la especie humana a lo largo de toda la historia, tanto por el número de enfermos como de muertos. Se ha calculado que en los últimos 200 años ha sido la responsable de la muerte de más de 1.000 millones de personas (1). La TB sigue siendo una de las enfermedades infecciosas más importante en esta época, y es el fiel reflejo de las enormes diferencias económicas y sociales que siguen existiendo en la población mundial1,2. Objetivo: describir las características demográficas y clínicas de los pacientes menores de 15 años con TB en el período 2011 – 2018 en un Hospital de cuarto nivel de la ciudad de Medellín – Colombia. Metodología: estudio observacional descriptivo de corte transversal. Incluyó pacientes menores de 15 años que asistieron al Hospital Universitario San Vicente Fundación (HUSVF) a quienes se les diagnosticó TB pulmonar y/o extrapulmonar, en el período comprendido entre enero de 2011 a diciembre de 2018. Resultados: 184 historias de pacientes con TB cumplieron los criterios de inclusión. Setenta y un pacientes (38.6 %) correspondían a TB pulmonar, 59 (32 %) a otras TB intratorácicas y 54 (29.3 %) a TB extrapulmonar. Las formas de TB más frecuentes fueron: ganglionar, del sistema nervioso central (SNC) y diseminada. De los niños menores de 5 años, el 50 % presentaron algún grado de desnutrición. La confirmación microbiológica por cultivo o baciloscopia (BK) estuvo presente en 91 pacientes (49.4 %) y por Reacción en Cadena de la Polimerasa (PCR) en 72 (39.1 %). Conclusiones: la TB infantil requiere un alto índice de sospecha. La suma de criterios es muy importante para su diagnóstico dada la fisiopatología de la enfermedad, sin embargo la búsqueda exhaustiva de la micobacteria es una estrategia útil para un tratamiento efectivo.

QuantiFERON-TB Gold In-tube test for the diagnosis of active and latent tuberculosis in selected health facilities of Addis Ababa, Ethiopia

Objective

To determine the performance of QuantiFERON-TB IN-Gold for the diagnosis active tuberculosis and latent tuberculosis.

Results

A total of 213 participants (136 tuberculosis suspects, 66 latently infected) were enrolled. Of 213, 21 (15.4%) of the tuberculosis suspects and 3 (4.5%) of the latent tuberculosis groups were human immunodeficiency virus infected. The sensitivity, specificity, positive and negative predictive value of QuantiFERON-TB IN-Gold for the diagnosis of active tuberculosis was 70.3% (26/37), 49.5% (49/99), 34.7% (26/75) and 83.1% (49/59) respectively. A kappa value of 0.316 (p = 0.001, 95% CI 1.605–1.609) between QuantiFERON-TB IN-Gold and tuberculin skin test were found.

Performance of the QuantiFERON-TB Gold Assay Among HIV-infected Children With Active Tuberculosis in France

BACKGROUND

Data regarding the use of QuantiFERON to assist the diagnosis of active tuberculosis (TB) in HIV-infected children are limited, especially in countries with low incidence of TB/HIV coinfection.

METHODS

QuantiFERON results were analyzed in 63 HIV-infected children who presented to our hospital in Paris, France. Seventeen HIV-uninfected children with active TB (4 culture-confirmed) were included for comparison.

RESULTS

The 63 HIV-infected children (median age: 11 yr) had 113 QuantiFERON tests. Thirty-four (54%) were born in sub-Saharan Africa. Vertical HIV transmission was documented for 50 of 52 (96%) and stage III HIV-infection for 30 of 50 children (60%). Over the study period, active TB was diagnosed in 7 of 63 HIV-infected children (3 culture-confirmed). Additional ongoing or previous opportunistic infections were present in 4 of 7. QuantiFERON results were positive in 2 of 7 HIV-infected children with active TB (sensitivity: 29%) and 16 of 17 HIV-uninfected children with active TB (sensitivity: 94%). At initial QuantiFERON testing of the 63 HIV-infected children, 8 (13%) had positive results (1, active TB; 5, latent TB; 2, previous TB) and 51 (81%) had negative results. Of 33 children with repeat testing after an initially positive or negative result, the only change was one conversion from a negative to a positive result at the onset of active TB. The 4 children (6%) with indeterminate quantiFERON results had a concomitant opportunistic infection. Results of repeat testing after clinical stabilization were negative in all 4.

CONCLUSIONS

QuantiFERON testing performed poorly for active TB diagnosis in this series of children with advanced HIV infection.

Accurate diagnosis of latent tuberculosis in children, people who are immunocompromised or at risk from immunosuppression and recent arrivals from countries with a high incidence of tuberculosis: systematic review and economic evaluation

BACKGROUND

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB) [(Zopf 1883) Lehmann and Neumann 1896], is a major cause of morbidity and mortality. Nearly one-third of the world's population is infected with MTB; TB has an annual incidence of 9 million new cases and each year causes 2 million deaths worldwide.

OBJECTIVES

To investigate the clinical effectiveness and cost-effectiveness of screening tests [interferon-gamma release assays (IGRAs) and tuberculin skin tests (TSTs)] in latent tuberculosis infection (LTBI) diagnosis to support National Institute for Health and Care Excellence (NICE) guideline development for three population groups: children, immunocompromised people and those who have recently arrived in the UK from high-incidence countries. All of these groups are at higher risk of progression from LTBI to active TB.

DATA SOURCES

Electronic databases including MEDLINE, EMBASE, The Cochrane Library and Current Controlled Trials were searched from December 2009 up to December 2014.

REVIEW METHODS

English-language studies evaluating the comparative effectiveness of commercially available tests used for identifying LTBI in children, immunocompromised people and recent arrivals to the UK were eligible. Interventions were IGRAs [QuantiFERON(®)-TB Gold (QFT-G), QuantiFERON(®)-TB Gold-In-Tube (QFT-GIT) (Cellestis/Qiagen, Carnegie, VA, Australia) and T-SPOT.TB (Oxford Immunotec, Abingdon, UK)]. The comparator was TST 5 mm or 10 mm alone or with an IGRA. Two independent reviewers screened all identified records and undertook a quality assessment and data synthesis. A de novo model, structured in two stages, was developed to compare the cost-effectiveness of diagnostic strategies.

RESULTS

In total, 6687 records were screened, of which 53 unique studies were included (a further 37 studies were identified from a previous NICE guideline). The majority of the included studies compared the strength of association for the QFT-GIT/G IGRA with the TST (5 mm or 10 mm) in relation to the incidence of active TB or previous TB exposure. Ten studies reported evidence on decision-analytic models to determine the cost-effectiveness of IGRAs compared with the TST for LTBI diagnosis. In children, TST (≥ 5 mm) negative followed by QFT-GIT was the most cost-effective strategy, with an incremental cost-effectiveness ratio (ICER) of £18,900 per quality-adjusted life-year (QALY) gained. In immunocompromised people, QFT-GIT negative followed by the TST (≥ 5 mm) was the most cost-effective strategy, with an ICER of approximately £18,700 per QALY gained. In those recently arrived from high TB incidence countries, the TST (≥ 5 mm) alone was less costly and more effective than TST (≥ 5 mm) positive followed by QFT-GIT or T-SPOT.TB or QFT-GIT alone.

LIMITATIONS

The limitations and scarcity of the evidence, variation in the exposure-based definitions of LTBI and heterogeneity in IGRA performance relative to TST limit the applicability of the review findings.

CONCLUSIONS

Given the current evidence, TST (≥ 5 mm) negative followed by QFT-GIT for children, QFT-GIT negative followed by TST (≥ 5 mm) for the immunocompromised population and TST (≥ 5 mm) for recent arrivals were the most cost-effective strategies for diagnosing LTBI that progresses to active TB. These results should be interpreted with caution given the limitations identified. The evidence available is limited and more high-quality research in this area is needed including studies on the inconsistent performance of tests in high-compared with low-incidence TB settings; the prospective assessment of progression to active TB for those at high risk; the relative benefits of two-compared with one-step testing with different tests; and improved classification of people at high and low risk for LTBI.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42014009033.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Comparison of Interferon-γ Release Assays and the Tuberculin Skin Test for Diagnosis of Tuberculosis in Human Immunodeficiency Virus: A Systematic Review

Background

It remains uncertain if interferon-γ release assays (IGRAs) are superior to the tuberculin skin test (TST) for the diagnosis of active tuberculosis (TB) or latent tuberculosis infection (LTBI) in immunosuppressed populations including people with human immunodeficiency virus (HIV) infection. The purpose of this study was to systematically review the performance of IGRAs and the TST in people with HIV with active TB or LTBI in low and high prevalence TB countries.

Methods

We searched the MEDLINE database from 1966 through to January 2017 for studies that compared results of the TST with either the commercial QuantiFERON-TB Gold in Tube (QFTGT) assay or previous assay versions, the T-SPOT.TB assay or in-house IGRAs. Data were summarized by TB prevalence. Tests for concordance and differences in proportions were undertaken as appropriate. The variation in study methodology was appraised.

Results

Thirty-two studies including 4,856 HIV subjects met the search criteria. Fourteen studies compared the tests in subjects with LTBI in low TB prevalence settings. The QFTGT had a similar rate of reactivity to the TST, although the first-generation version of that assay was reactive more commonly. IGRAs were more frequently positive than the TST in HIV infected subjects with active TB. There was considerable study methodology and population heterogeneity, and generally low concordance between tests. Both the TST and IGRAs were affected by CD4 T-cell immunodeficiency.

Conclusion

Our review of comparative data does not provide robust evidence to support the assertion that the IGRAs are superior to the TST when used in HIV infected subjects to diagnose either active TB or LTBI.

Interferon-gamma release assay for the diagnosis of latent tuberculosis infection: A latent-class analysis

BACKGROUND

Accurate diagnosis and subsequent treatment of latent tuberculosis infection (LTBI) is essential for TB elimination. However, the absence of a gold standard test for diagnosing LTBI makes assessment of the true prevalence of LTBI and the accuracy of diagnostic tests challenging. Bayesian latent class models can be used to make inferences about disease prevalence and the sensitivity and specificity of diagnostic tests using data on the concordance between tests. We performed the largest meta-analysis to date aiming to evaluate the performance of tuberculin skin test (TST) and interferon-gamma release assays (IGRAs) for LTBI diagnosis in various patient populations using Bayesian latent class modelling.

METHODS

Systematic search of PubMeb, Embase and African Index Medicus was conducted without date and language restrictions on September 11, 2017 to identify studies that compared the performance of TST and IGRAs for LTBI diagnosis. Two IGRA methods were considered: QuantiFERON-TB Gold In Tube (QFT-GIT) and T-SPOT.TB. Studies were included if they reported 2x2 agreement data between TST and QFT-GIT or T-SPOT.TB. A Bayesian latent class model was developed to estimate the sensitivity and specificity of TST and IGRAs in various populations, including immune-competent adults, immune-compromised adults and children. A TST cut-off value of 10 mm was used for immune-competent subjects and 5 mm for immune-compromised individuals.

FINDINGS

A total of 157 studies were included in the analysis. In immune-competent adults, the sensitivity of TST and QFT-GIT were estimated to be 84% (95% credible interval [CrI] 82-85%) and 52% (50-53%), respectively. The specificity of QFT-GIT was 97% (96-97%) in non-BCG-vaccinated and 93% (92-94%) in BCG-vaccinated immune-competent adults. The estimated figures for TST were 100% (99-100%) and 79% (76-82%), respectively. T-SPOT.TB has comparable specificity (97% for both tests) and better sensitivity (68% versus 52%) than QFT-GIT in immune-competent adults. In immune-compromised adults, both TST and QFT-GIT display low sensitivity but high specificity. QFT-GIT and TST are equally specific (98% for both tests) in non-BCG-vaccinated children; however, QFT-GIT is more specific than TST (98% versus 82%) in BCG-vaccinated group. TST is more sensitive than QFT-GIT (82% versus 73%) in children.

CONCLUSIONS

This study is the first to assess the utility of TST and IGRAs for LTBI diagnosis in different population groups using all available data with Bayesian latent class modelling. Our results challenge the current beliefs about the performance of LTBI screening tests, and have important implications for LTBI screening policy and practice. We estimated that the performance of IGRAs is not as reliable as previously measured in the general population. However, IGRAs are not or minimally affected by BCG and should be the preferred tests in this setting. Adoption of IGRAs in settings where BCG is widely administered will allow for a more accurate identification and treatment of LTBI.

Quantitative IFN-γ and IL-2 Response Associated with Latent Tuberculosis Test Discordance in HIV-infected Pregnant Women

RATIONALE

Pregnant women with latent tuberculosis infection (LTBI) are at high risk for development of TB, especially if infected with HIV.

OBJECTIVES

To assess the performance of LTBI tests in pregnant and postpartum women infected with HIV, investigate the immunology behind discordance in pregnancy, and explore the implications for the development of postpartum TB.

METHODS

We screened pregnant women in their second/third trimester and at delivery for LTBI using the tuberculin skin test (TST) and IFN-γ release assay (IGRA) (QuantiFERON Gold). A subset of antepartum women had longitudinal testing, with repeat testing at delivery and postpartum and additional cytokines measured from the IGRA supernatant. The kappa statistic and Wilcoxon rank sum test were used to determine agreement and comparison of cytokine concentrations, respectively.

MEASUREMENTS AND MAIN RESULTS

Of 252 enrolled, 71 (28%) women had a positive IGRA but only 27 (10%) had a positive TST (P < 0.005). There was 75% agreement (kappa, 0.25). When stratified by pregnancy versus delivery, 20% had IGRA(+)/TST(-) discordance at each time point. A positive IGRA was associated with known TB contact (odds ratio, 3.6; confidence interval, 1.2-11.1; P = 0.02). Compared with IGRA(+)/TST(+), women with IGRA(+)/TST(-) discordance had significantly less IFN-γ (1.85 vs. 3.48 IU/ml; P = 0.02) and IL-2 (46.17 vs. 84.03 pg/ml; P = 0.01). Five developed postpartum TB, of which three had IGRA(+)/TST(-) discordance during pregnancy.

CONCLUSIONS

Choice of LTBI test in pregnant women infected with HIV affects results. Pregnant women with IGRA(+)/TST(-) discordance had less IFN-γ and IL-2 than those with concordant-positive results and may represent an especially high-risk subset for the development of active TB postpartum.

The cursed duet today: Tuberculosis and HIV-coinfection

The tuberculosis (TB) and HIV syndemic continues to rage and are a major public health concern worldwide. This deadly association raises complexity and represent a significant barrier towards TB elimination. TB continues to be the leading cause of death amongst HIV-infected people. This paper reports the challenges that lay ahead and outlines some of the current and future strategies that may be able to address this co-epidemic efficiently. Improved diagnostics, cheaper and more effective drugs, shorter treatment regimens for both drug-sensitive and drug-resistant TB are discussed. Also, special topics on drug interactions, TB-IRIS and TB relapse are also described. Notwithstanding the defeats and meagre investments, diagnosis and management of the two diseases have seen significant and unexpected improvements of late. On the HIV side, expansion of ART coverage, development of new updated guidelines aimed at the universal treatment of those infected, and the increasing availability of newer, more efficacious and less toxic drugs are an essential element to controlling the two epidemics. On the TB side, diagnosis of MDR-TB is becoming easier and faster thanks to the new PCR-based technologies, new anti-TB drugs active against both sensitive and resistant strains (i.e. bedaquiline and delamanid) have been developed and a few more are in the pipeline, new regimens (cheaper, shorter and/or more effective) have been introduced (such as the "Bangladesh regimen") or are being tested for MDR-TB and drug-sensitive-TB. However, still more resources will be required to implement an integrated approach, install new diagnostic tests, and develop simpler and shorter treatment regimens.

Performance of point-of-care urine test in diagnosing tuberculosis suspects with and without HIV infection in selected peripheral health settings of Addis Ababa, Ethiopia

Background

There are few rapid point-of-care tests (POCT) for tuberculosis (TB) for use in resource-constrained settings with high levels of human immunodeficiency virus (HIV). This hinders early tuberculosis (TB) treatment. This cross-sectional study evaluates the recently developed urine Determine tuberculosis lipoarabinomannan (TB LAM) antigen test. A total of 122 participants with signs and symptoms of TB, including 21 (17.1%) participants positive for HIV, were enrolled from September 2011 to March 2012 at three selected health centers in Addis Ababa, Ethiopia. Blood, sputum and urine samples were collected. Löwenstein-Jensen (LJ) solid culture was used as a gold standard to evaluate the performance of the Determine TB LAM antigen test. Data were analyzed using STATA (Statacorp LP, USA).

Results

Of the 122 participants with suspected TB, 35 (28.7%) had TB confirmed bacteriologically by LJ culture. The overall sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of Determine TB LAM (for both HIV-positive and HIV-negative participants) was 37.1% (95% CI 21.5–55.1), 97.7% (95% CI 91.9–99.7), 86.7% (95% CI 59.5–98.3) and 79.4% (95% CI 70.5–86.6), respectively. However, in participants who were co-infected with TB and HIV, sensitivity, specificity, PPV and NPV were 55.6% (95% CI 21.2–86.3), 100% (95% CI 73.5–100), 100% (95% CI 47.8–100) and 75.0% (95% CI 47.6–92.7). Moreover, the level of immunosuppression of the HIV-infected TB patients was found to have a significant association with the performance of Determine TB LAM (χ² = 7.89, p = 0.002).

Conclusions

The Determine TB LAM test is a potential alternative in peripheral health settings for TB diagnosis in patients who are co-infected with HIV, with advanced immunosuppression.

Screening and treatment of latent tuberculosis infection among HIV-infected patients in resource-rich settings

Current international guidelines recommend screening and treatment of latent tuberculosis (TB) infection in HIV-infected patients in all settings. The main factors affecting the risk of TB in HIV-infected patients include the level of immunosuppression, coverage of antiretroviral therapy and local TB burden. In resource-rich settings where antiretroviral therapy is more accessible and HIV-infected patients are expected to be diagnosed at an earlier stage, local TB burden remains a key factor on their risk of TB. This article reviewed the epidemiology of latent TB infection among the adult HIV-infected patients, and the use and benefit of screening and treatment of latent TB infection in resource-rich settings in the past decade. While such practice should be continued in countries with medium or high TB burden, targeted screening and treatment only for HIV-infected patients with additional risk factors for TB might be a more practical option in resource-rich countries with low TB burden.

The Clinical Usefulness of Tuberculin Skin Test versus Interferon-Gamma Release Assays for Diagnosis of Latent Tuberculosis in HIV Patients: A Meta-Analysis

BACKGROUND

Accurate diagnosis of latent tuberculosis infection (LTBI) is becoming increasingly concerning due to the increasing the HIV epidemic, which have increased the risk for reactivation to active tuberculosis (TB) infection. LTBI is diagnosed by tuberculin skin test (TST) and interferon-gamma release assays (IGRAs).

OBJECTIVES

The aim of the present study was to conduct a meta-analysis of published papers on the agreement (kappa) between TST and QuantiFERON-TB Gold In-Tube (QFT-GIT) tests for diagnosis of LTBI in HIV patient.

METHODS

Electronic databases including PubMed/Medline, Elsevier/Scopus and Embase/Ovid were reviewed up Jan. 2016. We performed a random effect model meta-analysis for estimation of pooled Kappa between the two methods of diagnosis. Meta regression was used for assessing potential heterogeneity and Egger's test was used for assessing small study effect and publication bias.

RESULTS

The initial search strategy produced 6744 records. Of them, 23 cross-sectional studies met the inclusion criteria and 20 studies entered in meta-analysis. The pooled kappa was and prevalence-adjusted and bias-adjusted kappa (PABAK) were 0.37 (95% CI: 0.28, 0.46) and 0.59 (0.49, 0.69). The discordance of TST-/QFT-GIT+ was more than TST+/QFT-GIT-. Kappa estimate between two tests was linearly associated with age and prevalence index and inversely associated with bias index.

CONCLUSION

Fair agreement between TST and QFT-GIT makes it difficult to know whether TST is as useful as the QFT-GIT in HIV-infected patients. The higher discordance of TST-/QFT-GIT+ in compared to TST+/QFT-GIT- can induce the higher sensitivity of QFT-GIT for diagnosis LTBI in HIV patients. Disagreement between two tests can be influenced by error in measurements and prevalence of HIV.

Utility of QuantiFERON-TB Gold In-Tube Test in the Diagnosis of Latent TB in HIV-Positive Patients in a Medium-TB Burden Country

BACKGROUND

The authors aimed to compare TST with QuantiFERON-TB Gold In-Tube (QFT) for detecting latent tuberculosis infection (LTBI) in HIV-infected patients in Iran as a TB-medium endemic country.

METHODS

In a cross-sectional design,130 HIV-positive patients in HIV clinic of Tehran University were studied. Patients screened for LTBI with QFT and TST simultaneously. Concordance between 2 tests results and variables associated with tests discordance were assessed.

RESULTS

Positive results found in 24.6% for TST and 7.7% for QFT. Overall agreement between them was 73.85% (Kappa = 0.083). History of imprisonment was associated with more positive TST (P = 0.014) and QFT (P = 0.01). Patients with intravenous drug use (IDU) history had significant discordant results (0.018).

CONCLUSION

The authors recommend QFT for all negative cases of TST in HIV-positive patients especially who had history of IDU.

Development and evaluation of a new interferon-gamma release assay for the diagnosis of tuberculosis infection in HIV-infected individuals in China

BACKGROUND

Human immunodeficiency virus (HIV)-infected individuals are at high risk of contracting tuberculosis (TB) disease, and current methods for diagnosing TB infection are less effective in this population. We developed and evaluated a new interferon-gamma release assay (IGRA), named A.TB, in HIV-infected individuals, with and without active TB, in a setting of high TB burden and low HIV prevalence.

METHODS

A total of 255 subjects were divided into 3 groups according to their HIV and TB status: HIV+ without active TB (n = 123), HIV+/TB+ (n = 79), and HIV-/TB+ (n = 65). The A.TB assay was performed in parallel with the QuantiFERON-TB Gold In-Tube (QFT-GIT) and tuberculin skin test (TST).

RESULTS

The positive rate was 59.3% (n = 123) by A.TB and 53.8% (n = 106) by QFT-GIT. We observed a strong concordance of 81.2% (k = 0.612) between the two IGRAs. The QFT-GIT results were affected by low CD4(+) cell count (p = 0.013), while A.TB results were not. A.TB was also performed in patients with active TB (n = 65) and patients with active TB and HIV co-infection (n = 79). The sensitivity of A.TB in these groups was 80.0% and 81.0%, respectively.

CONCLUSION

The A.TB results were not affected by low CD4(+) cell count in the co-infected cohort. With further evaluation, A.TB may prove to be a valuable tool for diagnosing TB in HIV-infected patients.

Tuberculin skin test and QuantiFERON-TB Gold In-tube Test for latent tuberculosis in Thai HIV-infected adults

BACKGROUND AND OBJECTIVE

Limited data exist for the performance of QuantiFERON-TB Gold In-tube Test (QFT-IT) in comparison to tuberculin skin test (TST) for detecting latent tuberculosis (LTB) in patients with human immunodeficiency virus (HIV) infection from tuberculosis (TB)-endemic Asia-Pacific countries.

METHODS

A cohort study of Thai HIV-infected patients without history of TB or LTB treatment was conducted from March 2012 through March 2013. Each patient underwent simultaneous TST and QFT-IT.

RESULTS

Among the 150 enrolled subjects, the median age was 40 years (range 17-65), 53% were male, and the median CD4 count was 367 cells/μL (range 8-1290). Reactive TST and positive QFT-IT were 16% and 13%, respectively, with low concordance between tests (kappa = 0.26); correlation between TST reaction size and level of interferon-γ was moderate (r = 0.34). Independent factors associated with discordant results were long-term smoking (adjusted odds ratio (aOR) 5.74; P = 0.002) for TST-reactive, QFT-IT-negative subjects, and age greater than 52 years (aOR 5.56; P = 0.02) and female gender (aOR 4.40; P = 0.04) for TST non-reactive, QFT-IT-positive subjects. The level of agreement between both tests improved when using a TST cut-off of ≥ 10 mm (kappa = 0.39).

CONCLUSIONS

In our setting where QFT-IT is available but has limited use due to cost, TST with a cut-off of 10 mm for reactivity should be the initial LTB test. HIV-infected women and persons older than 52 years with non-reactive TST and long-term smokers with reactive TST may benefit from subsequent QFT-IT.

Poor agreement between interferon-gamma release assays and the tuberculin skin test among HIV-infected individuals in the country of Georgia

BACKGROUND

Improved tests to diagnose latent TB infection (LTBI) are needed. We sought to evaluate the performance of two commercially available interferon-gamma release assays (IGRAs) compared to the tuberculin skin test (TST) for the diagnosis of LTBI and to identify risk factors for LTBI among HIV-infected individuals in Georgia, a country with high rates of TB.

METHODS

HIV-patients were enrolled from the National AIDS Center in Tbilisi, Georgia. After providing informed consent, each participant completed a questionnaire, had blood drawn for QuantiFERON-TB Gold in-Tube (QFT-GIT) and T-SPOT.TB testing and had a TST placed. The TST was read at 48-72 hrs with ≥ 5 mm induration considered positive.

RESULTS

Between 2009-2011, 240 HIV-infected persons (66% male) with a median age of 38 years and a median CD4 count of 255 cells/μl (IQR: 124-412) had diagnostic testing for LTBI performed. 94% had visible evidence of a BCG scar. The TST was positive in 41 (17%) patients; QFT-GIT in 70 (29%); and T-SPOT.TB in 56 (24%). At least one diagnostic test was positive in 109 (45%) patients and only among 13 (5%) patients were all three tests positive. Three (1%) QFT-GIT and 19 (8%) T-SPOT.TB test results were indeterminate. The agreement among all pairs of tests was poor: QFT-GIT vs. T-SPOT.TB (κ = 0.18, 95% CI .07-.30), QFT-GIT vs. TST (κ = 0.29, 95% CI .16-.42), and TST vs. T-SPOT.TB (κ = 0.22, 95% CI .07-.29). Risk factors for LTBI varied by diagnostic test and none showed associations between positive test results and well-known risk factors for TB, such as imprisonment, drug abuse and immunological status.

CONCLUSIONS

A high proportion of HIV patients had at least one positive diagnostic test for LTBI; however, there was very poor agreement among all tests. This lack of agreement makes it difficult to know which test is superior and most appropriate for LTBI testing among HIV-infected patients. While further follow-up studies will help determine the predictive ability of different LTBI tests, improved modalities are needed for accurate detection of LTBI and assessment of risk of developing active TB among HIV-infected patients.

The proportions of people living with HIV in low and middle-income countries who test tuberculin skin test positive using either a 5 mm or a 10 mm cut-off: a systematic review

Background

A positive tuberculin skin test (TST) is often defined by skin induration of ≥10 mm in people who are HIV-seronegative. However, to increase sensitivity for detection of Mycobacterium tuberculosis infection in the context of impaired immune function, a revised cut-off of ≥5 mm is used for people living with HIV infection. The incremental proportion of patients who are included by this revised definition and the association between this proportion and CD4+ cell count are unknown.

Methods

The literature was systematically reviewed to determine the proportion of people living with HIV (PLWH) without evidence of active tuberculosis in low and middle-income countries who tested TST-positive using cut-offs of ≥5 mm and ≥10 mm of induration. The difference in the proportion testing TST-positive using the two cut-off sizes was calculated for all eligible studies and was stratified by geographical region and CD4+ cell count.

Results

A total of 32 studies identified meeting criteria were identified, providing data on 10,971 PLWH from sub-Saharan Africa, Asia and the Americas. The median proportion of PLWH testing TST-positive using a cut-off of ≥5 mm was 26.8% (IQR, 19.8-46.1%; range, 2.5-81.0%). Using a cut-off of ≥10 mm, the median proportion of PLWH testing TST-positive was 19.6% (IQR, 13.7-36.8%; range 0–52.1%). The median difference in the proportion of PLWH testing TST-positive using the two cut-offs was 6.0% (IQR, 3.4-10.1%; range, 0–37.6%). Among those with CD4+ cell counts of <200, 200–499 and ≥500 cells/μL, the proportion of positive tests defined by the ≥5 mm cut-off that were between 5.0 and 9.9 mm in diameter was similar (12.5%, 12.9% and 10.5%, respectively).

Conclusions

There is a small incremental yield in the proportion of PLWH who test TST-positive when using an induration cut-off size of ≥5 mm compared to ≥10 mm. This proportion was similar across the range of CD4+ cell strata, supporting the current standardization of this cut-off at all levels of immunodeficiency.

The performance of quantiferon-TB gold in-tube (QFT-IT) test compared to tuberculin skin test (TST) in detecting latent tuberculosis infection (LTBI) in the presence of HIV coinfection in a high TB-burden area with BCG-vaccinated population

OBJECTIVES

To compare quantiferon-TB gold "in tube" (QFT-IT) with the conventional tuberculin skin test (TST) for the diagnosis of latent tuberculosis infection (LTBI) in HIV-infected adults in a setting highly endemic for tuberculosis with BCG vaccinated population in Bangalore, Karnataka, India.

PATIENTS AND METHODS

The study population (100 BCG-vaccinated adults) was divided into 4 groups: HIV patients with TB patient contact, HIV patients with past history of TB, TB patients (positive control), and healthy volunteers (negative control).

RESULTS

Overall agreement between TST and QFT-IT was 52.4% (κ = 0.22). Increasing the TST cutoff value from 5 mm to 10 mm among HIV-positive groups resulted in better agreement 62.5% in Group 1 and 81.2% in Group 2.

DISCUSSION

In a setting with high TB prevalence, the TST gives increased false positives in HIV-positive groups if 5 mm is used as the cutoff value. This could be minimized by increasing the cutoff to 10 mm.

CONCLUSION

The 2-step approach (initial testing of all cases with TST and confirmation of only those positive in TST by testing with QFT-IT) will be economical and help in treating LTBI cases in lower middle income countries like India.

Systematic review of TST responses in people living with HIV in under-resourced settings: implications for isoniazid preventive therapy

BACKGROUND

People living with HIV (PLWH) who have positive tuberculin skin tests (TST) benefit from isoniazid preventive therapy (IPT) whereas those testing TST-negative do not. Revised World Health Organization guidelines explicitly state that assessment of TST is not a requirement for initiation of IPT. However, it is not known what proportions of patients will benefit from IPT if implemented without targeting according to TST status. We therefore determined the proportions of PLWH who test TST-positive.

METHODOLOGY/PRINCIPAL FINDINGS

We systematically reviewed the literature published between January 1990 and February 2012 to determine the proportions of patients without active tuberculosis attending HIV care services in low and middle-income countries who tested TST-positive (≥5 mm induration). Proportions were also determined for different CD4 count strata. Data from 19 studies with 9,478 PLWH from sub-Saharan Africa, Asia and Central and South America were summarized. The vast majority were not receiving antiretroviral therapy (ART). A sub-analysis was conducted of 5 studies (5,567 subjects) from high TB prevalence countries of PLWH with negative TB screens attending HIV care and treatment settings for whom CD4 stratified data were available. The median proportion of PLWH testing TST-positive overall was 22.8% (range, 19.5-32.6%). The median (range) proportions with CD4 cell counts of <200, 200-499 or ≥500 cells/µL who tested positive were 12.4% (8.2-15.3%), 28.4% (20.1-36.9%) and 37.4% (31.3-56.3%), respectively. Heterogeneity in the data precluded calculation of pooled summary estimates.

CONCLUSIONS/SIGNIFICANCE

In most settings, if IPT is administered to PLWH pre-ART without assessment of TST status, only a minority of those treated are likely to benefit, especially among those with the lowest CD4 cell counts. This may be inefficient use of resources and cost-effectiveness analyses should take this into account. Local knowledge of TST response rates may help inform policies. New simple means of identifying those who will benefit from IPT are needed to permit appropriate targeting of this intervention.

Contribution of interferon gamma release assays testing to the diagnosis of latent tuberculosis infection in HIV-infected patients: a comparison of QuantiFERON-TB Gold In Tube, T-SPOT.TB and tuberculin skin test

BACKGROUND

Diagnosis and treatment of latent tuberculosis infection (LTBI) is the most effective strategy to control tuberculosis (TB) among patients with HIV infection. The tuberculin skin test (TST) was the only available method to identify LTBI. The aim of the present work was to evaluate the usefulness of the interferon-gamma release assays (IGRAs): QuantiFERON-tuberculosis (TB) Gold-In-Tube test (QFG) and T-SPOT.TB for the diagnosis of LTBI in a diverse cohort of HIV-infected patients.

METHODS

A prospective study was carried out in consecutive patients cared for in a single institution in Spain from January 2009 to October 2010. IGRAs and TST were performed simultaneously. TST induration ≥ 5 mm was considered positive.

RESULTS

QFG, T-SPOT.TB and TST were performed in 373 subjects. Median CD4 cell count was 470/μl with a median nadir of 150/μl. TST, QFG and T-SPOT.TB were positive in 13.3%, 7.5% and 18.5% cases respectively. Among 277 patients with neither past or current TB nor previous treatment for LTBI and who had TST results, a positive TST result was obtained in 20 (7.2%) cases. When adding QFG results to TST, there were a total of 26 (8.6%) diagnoses of LTBI. When the results of both IGRAs were added, the number of diagnoses increased to 54 (17.9%) (incremental difference: 10.7% [95% confidence interval [CI]:5.3-16.2%] [p < 0.001]), and when both IGRAs were added, the number of diagnoses reached 56 (18.5%) (incremental difference: 11.3% [95% CI:5.7%-16.9%] [p < 0.001]). Patients with a CD4 cell count greater than 500 cells/μl and prior stay in prison were more likely to have a diagnosis of LTBI by TST and/or QFG and/or T-SPOT.TB (adjusted odds ratio [aOR]: 3.8; 95% CI, 1.4 - 9.9; and aOR: 3.3; 95% CI, 1.3 - 8.3, respectively).

CONCLUSIONS

IGRAs were more sensitive than TST for diagnosis of M. tuberculosis infection in HIV-infected patients. Dual sequential testing with TST and IGRAs may be the optimal approach for LTBI screening in this population.

Comparison of interferon gamma-inducible protein-10 and interferon gamma-based QuantiFERON TB Gold assays with tuberculin skin test in HIV-infected subjects

We aimed to compare the positivity of the QuantiFERON TB gold in-tube (QFT-IT antigens) specific interferon gamma (IFN-γ/QFT-IT) and IFN-γ-inducible protein-10 (IP-10/QFT-IT) assays with tuberculin skin test (TST) among human immunodeficiency virus (HIV)-infected individuals in a TB endemic setting. A total of 180 HIV-infected subjects, with no evidence of active TB, were recruited. IFN-γ and IP-10 levels specific to QFT-IT antigens were measured in plasma from QFT-IT tubes. The overall positivity of TST at the 5-mm cut-off point (19%) was significantly lower when compared to IFN-γ/QFT-IT (38%) and IP-10/QFT-IT (45%) assays. The positivity of IP-10/QFT-IT was significantly higher than that of IFN-γ/QFT-IT (P = 0.038). Indeterminate results for IFN-γ/QFT-IT and IP-10/QFT-IT were more frequent in subjects with CD4 count <100 cells/μL than in those with >100 cells/μL. IFN-γ/QFT-IT (9%) yielded significantly higher number of indeterminate results than IP-10/QFT-IT (5%). The frequency of these responses is higher than the proportion of individuals with positive TST results. However, 6 IFN-γ/QFT-IT- or IP-10/QFT-IT-negative subjects were positive for TST at the 5-mm cut-off point. Prospective and prognostic studies are required to clarify the significance of these data.

Improved sensitivity of an interferon-gamma release assay (T-SPOT.TB™) in combination with tuberculin skin test for the diagnosis of latent tuberculosis in the presence of HIV co-infection

BACKGROUND

Interferon-gamma release assays (IGRA) are more specific than the tuberculin skin test (TST) for the diagnosis of Mycobacterium tuberculosis infection. Data on sensitivity are controversial in HIV infection.

METHODS

IGRA (T-SPOT.TB) was performed using lymphocytes stored within 6 months before culture-confirmed tuberculosis was diagnosed in HIV-infected individuals in the Swiss HIV Cohort Study.

RESULTS

64 individuals (69% males, 45% of non-white ethnicity, median age 35 years (interquartile range [IQR] 31-42), 28% with prior AIDS) were analysed. Median CD4 cell count was 223 cells/μl (IQR 103-339), HIV-RNA was 4.7 log10 copies/mL (IQR 4.3-5.2). T-SPOT.TB resulted positive in 25 patients (39%), negative in 18 (28%) and indeterminate in 21 (33%), corresponding to a sensitivity of 39% (95% CI 27-51%) if all test results were considered, and 58% (95% CI 43-74%) if indeterminate results were excluded. Sensitivity of IGRA was independent of CD4 cell count (p = 0.698). Among 44 individuals with available TST, 22 (50%) had a positive TST. Agreement between TST and IGRA was 57% (kappa = 0.14, p = 0.177), and in 34% (10/29) both tests were positive. Combining TST and IGRA (at least one test positive) resulted in an improved sensitivity of 67% (95% CI 52-81%). In multivariate analysis, older age was associated with negative results of TST and T-SPOT.TB (OR 3.07, 95% CI 1,22-7.74, p = 0.017, per 10 years older).

CONCLUSIONS

T-SPOT.TB and TST have similar sensitivity to detect latent TB in HIV-infected individuals. Combining TST and IGRA may help clinicians to better select HIV-infected individuals with latent tuberculosis who qualify for preventive treatment.

Performance of QuantiFERON-TB Gold test compared to tuberculin skin test in detecting latent tuberculosis infection in HIV- positive individuals in Iran

BACKGROUND:

There is limited data about the performance of QuantiFERON-TB Gold (QFT-G) test in detecting latent tuberculosis infection (LTBI) in our region. We intended to determine the performance of QFT-G compared to conventional tuberculin skin test (TST) in detecting LTBI in HIV-positive individuals in Iran.

METHODS:

This study was conducted in a HIV clinic in Tehran, Iran in April 2007. A total of 50 consecutive HIV-positive patients, not currently affected with active tuberculosis (TB), were recruited; 43 (86%) were male. The mean age was 38 ± 7.2 years (21–53). All had history of Bacillus Calmette Guerin (BCG) vaccination. A TST with purified protein derivative (PPD) and whole-blood interferon-gamma release assay (IGRA) in reaction to ESAT-6 and CFP-10 antigens was performed and measured by enzyme-linked immuno-sorbent assay (ELISA). The agreement between TST and QFT-G results were analyzed using Kappa test.

RESULTS:

A total of 36 (72%) patients had negative and 14 (28%) revealed positive TST. For QFT-G, 20 (40%) tested positive, 19 (38%) tested negative, and the results in 11 cases (22%) were indeterminate. A total of 14 (28%) patients had a CD4 count of <200. Of the 14, TST + group, 12 had QFT-G +, only one case TST+/QFT-G-, and QFT-G was indeterminate in one TST positive case. Of the 36 patients with negative TST tests, 8 (22%) had positive GFT-G and 10 (28%) yielded indeterminate results. There was no association between a positive TST and receiving highly active anti-retroviral therapy (HAART) or absolute CD4 counts. Similarly, the association between QFT-G results and receiving HAART or CD4 counts was not significant (P = 0.06). Although TST results were not significantly different in patients with CD4 < 200 vs. CD4 >200 (P = 0.295), association between QFT-G results and CD4 cutoff of 200 reached statistical significance (P = 0.027). Agreement Kappa coefficient between TST and QFT-G was 0.54 (Kappa = 0.54, 95% CI = 38.4-69.6,P < 0.001).

CONCLUSION:

Detecting LTBI in HIV-positive individuals showed moderate agreement between QFT-G and LTBI in our study. Interestingly, our findings revealed that nontuberculous mycobacteria and prior BCG vaccination have minimal influence on TST results in HIV patients in Iran.

Community-based cross-sectional survey of latent tuberculosis infection in Afar pastoralists, Ethiopia, using QuantiFERON-TB Gold In-Tube and tuberculin skin test

Background

There is little information concerning community-based prevalence of latent tuberculosis infection (LTBI) using T-cell based interferon-γ (IFN-γ) release assays (IGRAs), particularly in TB endemic settings. In this study, the prevalence of LTBI in the Afar pastoral community was assessed using QuantiFERON-TB Gold In-Tube (QFTGIT) and tuberculin skin tests (TST).

Methods

A community-based cross-sectional survey of LTBI involving 652 apparently healthy adult pastoralists was undertaken in the pastoral community of Amibara District of the Afar Region between April and June 2010.

Results

The prevalence of LTBI was estimated as 63.7% (363/570) using QFTGIT at the cut-off point recommended by the manufacturer (≥ 0.35 IU/ml IFN-γ), while it was 74.9% (427/570) using a cut-off point ≥ 0.1 IU/ml IFN-γ. The QFTGIT-based prevalence of LTBI was not significantly associated with the gender or age of the study participants. However, the prevalence of LTBI was 31.2% (183/587) using TST at a cut-off point ≥ 10 mm of skin indurations, and it was higher in males than females (36.8% vs. 23.5%, X² = 11.76; p < 0.001). There was poor agreement between the results of the tests (k = 0.098, 95% CI, 0.08 - 0.13). However, there was a positive trend between QFTGIT and TST positivity (X² = 96.76, P < 0.001). Furthermore, individuals with skin indurations ≥ 10 mm were 13.6 times more likely to have positive results using QFTGIT than individuals with skin indurations of 0 mm (adjusted OR = 13.6; 95%CI, 7.5 to 24.7, p < 0.001).

Conclusions

There is currently no agreed gold standard for diagnosis of LTBI. However, the higher prevalence of LTBI detected using QFTGIT rather than TST suggests that QFTGIT could be used for epidemiological studies concerning LTBI at the community level, even in a population unreactive to TST. Further studies of adults and children will be required to assess the effects of factors such as malnutrition, non-tuberculosis mycobacterial infections, HIV and parasitic infections on the performance of QFTGIT.

Risk factors associated with positive QuantiFERON-TB Gold In-Tube and tuberculin skin tests results in Zambia and South Africa

Introduction

The utility of T-cell based interferon-gamma release assays for the diagnosis of latent tuberculosis infection remains unclear in settings with a high burden of tuberculosis.

Objectives

To determine risk factors associated with positive QuantiFERON-TB Gold In-Tube (QFT-GIT) and tuberculin skin test (TST) results and the level of agreement between the tests; to explore the hypotheses that positivity in QFT-GIT is more related to recent infection and less affected by HIV than the TST.

Methods

Adult household contacts of tuberculosis patients were invited to participate in a cross-sectional study across 24 communities in Zambia and South Africa. HIV, QFT-GIT and TST tests were done. A questionnaire was used to assess risk factors.

Results

A total of 2,220 contacts were seen. 1,803 individuals had interpretable results for both tests, 1,147 (63.6%) were QFT-GIT positive while 725 (40.2%) were TST positive. Agreement between the tests was low (kappa = 0.24). QFT-GIT and TST results were associated with increasing age (adjusted OR [aOR] for each 10 year increase for QFT-GIT 1.15; 95% CI: 1.06–1.25, and for TST aOR: 1.10; 95% CI 1.01–1.20). HIV positivity was less common among those with positive results on QFT-GIT (aOR: 0.51; 95% CI: 0.39–0.67) and TST (aOR: 0.61; 95% CI: 0.46–0.82). Smear positivity of the index case was associated with QFT-GIT (aOR: 1.25; 95% CI: 0.90–1.74) and TST (aOR: 1.39; 95% CI: 0.98–1.98) results. We found little evidence in our data to support our hypotheses.

Conclusion

QFT-GIT may not be more sensitive than the TST to detect risk factors associated with tuberculous infection. We found little evidence to support the hypotheses that positivity in QFT-GIT is more related to recent infection and less affected by HIV than the TST.

Interferon-gamma release assays for the diagnosis of latent tuberculosis infection in HIV-infected individuals: a systematic review and meta-analysis

OBJECTIVE

To determine whether interferon-gamma release assays (IGRAs) improve the identification of HIV-infected individuals who could benefit from latent tuberculosis infection therapy.

DESIGN

Systematic review and meta-analysis.

METHODS

We searched multiple databases through May 2010 for studies evaluating the performance of the newest commercial IGRAs (QuantiFERON-TB Gold In-Tube [QFT-GIT] and T-SPOT.TB [TSPOT]) in HIV-infected individuals. We assessed the quality of all studies included in the review, summarized results in prespecified subgroups using forest plots, and where appropriate, calculated pooled estimates using random effects models.

RESULTS

The search identified 37 studies that included 5736 HIV-infected individuals. In three longitudinal studies, the risk of active tuberculosis was higher in HIV-infected individuals with positive versus negative IGRA results. However, the risk difference was not statistically significant in the two studies that reported IGRA results according to manufacturer-recommended criteria. In persons with active tuberculosis (a surrogate reference standard for latent tuberculosis infection), pooled sensitivity estimates were heterogeneous but higher for TSPOT (72%; 95% confidence interval [CI], 62-81%) than for QFT-GIT (61%; 95% CI, 47-75%) in low-/middle-income countries. However, neither IGRA was consistently more sensitive than the tuberculin skin test in head-to-head comparisons. Although TSPOT appeared to be less affected by immunosuppression than QFT-GIT and the tuberculin skin test, overall, differences among the three tests were small or inconclusive.

CONCLUSIONS

Current evidence suggests that IGRAs perform similarly to the tuberculin skin test at identifying HIV-infected individuals with latent tuberculosis infection. Given that both tests have modest predictive value and suboptimal sensitivity, the decision to use either test should be based on country guidelines and resource and logistic considerations.

Impact of peripheral lymphocyte count on the sensitivity of 2 IFN-gamma release assays, QFT-G and ELISPOT, in patients with pulmonary tuberculosis

OBJECTIVE

This study evaluated the effect of peripheral lymphocyte count on 2 interferon-gamma release assays [QuantiFERON TB-Gold (QFT-G) and enzyme-linked immunospot (ELISPOT)] and their sensitivity in patients with pulmonary tuberculosis, including HIV-negative immunocompromised patients.

PATIENTS AND METHODS

Two hundred thirty patients with microbiologically confirmed active pulmonary tuberculosis were subjected to the tests. Lymphocyte counts were analyzed simultaneously.

RESULTS

Overall sensitivity was 74% (159/215; 95% CI, 68-80%) for QFT-G and 92% (198/215; 89-96%) for ELISPOT (p<0.0001). In patients with peripheral lymphocyte counts of > or =1000/microL, sensitivity was high for both QFT-G (88%, 111/126; 82-94%) and ELISPOT (97%, 122/126; 94-100%). However, the sensitivity decreased significantly with decreasing peripheral lymphocyte count for both QFT-G (test for trend p<0.0001) and ELISPOT (test for trend p=0.007). When lymphocyte counts were <500/microL, the sensitivity was 81% (25/31; 66-96%) for ELISPOT, but only 39% (12/31; 21-57%) for QFT-G.

CONCLUSION

Both QFT-G and ELISPOT are sensitive methods for detecting active pulmonary tuberculosis, but their sensitivity partly depends on peripheral lymphocyte counts. At low lymphocyte count conditions, ELISPOT is superior to QFT-G for detecting tuberculosis, irrespective of age, gender, and nutrition.

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.

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.

Usefulness of interferon-gamma release assays for diagnosing TB infection and problems with these assays

The specificity of the tuberculin skin test (TST) in the diagnosis of tuberculosis infection is seriously compromised because of extensive use of the bacille Calmette-Guérin (BCG) vaccination. The interferon-gamma release assay (IGRA), a new diagnostic using Mycobacterium tuberculosis-specific antigens has been introduced in response to these needs. In this review, published findings on the performance of the QuantiFERON-TB (QFT), one of the IGRA formats, are summarized and discussed. In addition to its high specificity, the QFT has considerably high sensitivity, comparable with or superior to that of the TST, if applied to patients with active tuberculosis as a surrogate of latent tuberculosis infection. When applied to patients with immunosuppression, such as aging patients, or those with HIV infection, those with immunosuppressive drug therapies, or those with renal hemodialysis, QFT is shown to be more robust than the TST. As regards the dynamics of QFT responses to chemotherapy, there are many reports showing a decrease in responses during the treatment, which indicates the possibility that QFT could be used as a tool for monitoring the progress of treatment. However, there are discordant reports that warrant further study.

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.

IFN-gamma release assays in tuberculosis management in selected high-risk populations

Tuberculosis (TB) is the most deadly infectious disease in the world. TB control relies on passive case findings and targeted treatment of latently infected individuals at high risk of disease progression. Tuberculin skin testing (TST) is conventionally used for detection of TB infection. Recently, blood assays measuring the release of IFN-gamma by TB-specific effector memory T cells have been developed to overcome TST limitations. Overall, IFN-gamma release assays are more specific than TST, more sensitive in detecting active TB and correlate better with TB exposure in immune-competent patients, at least in low-burden settings. There are three US FDA-approved assays commercially available: the ELISpot-based assay T-SPOT.TB (Oxford Immunotech, UK) and two ELISA-based formats, QuantiFERON TB Gold (QFT) and QFT-in tube (Cellestis, Australia). Recent international guidelines and consensus statements recommend the use of IFN-gamma release assays at different levels in TB management. However, conclusive evidence-based information targeting populations at high TB risk, including HIV-infected individuals, children and patient candidates for biotherapy with TNF-alpha blockers, are lacking. The aim of this review is to focus our attention on studies addressing the performance of commercial IFN-gamma release assays in clinical management of TB infection in these highly selected settings to provide a more comprehensive picture of the actual scenario and to identify areas to be investigated further.

Role of interferon gamma release assay in active TB diagnosis among HIV infected individuals

Background

A rapid and specific test is urgently needed for tuberculosis (TB) diagnosis especially among human immunodeficiency virus (HIV) infected individuals. In this study, we assessed the sensitivity of Interferon gamma release assay (IGRA) in active tuberculosis patients who were positive for HIV infection and compared it with that of tuberculin skin test (TST).

Methodology/Principal Findings

A total of 105 HIV-TB patients who were naïve for anti tuberculosis and anti retroviral therapy were included for this study out of which 53 (50%) were culture positive. Of 105 tested, QuantiFERON-TB Gold in-tube (QFT-G) was positive in 65% (95% CI: 56% to 74%), negative in 18% (95% CI: 11% to 25%) and indeterminate in 17% (95% CI: 10% to 24%) of patients. The sensitivity of QFT-G remained similar in pulmonary TB and extra-pulmonary TB patients. The QFT-G positivity was not affected by low CD4 count, but it often gave indeterminate results especially in individuals with CD4 count <200 cells/µl. All of the QFT-G indeterminate patients whose sputum culture were positive, showed ≤0.25 IU/ml of IFN-γ response to phytohemagglutinin (PHA). TST was performed in all the 105 patients and yielded the sensitivity of 31% (95% CI: 40% to 22%). All the TST positives were QFT-G positives. The sensitivity of TST was decreased, when CD4 cell counts declined.

Conclusions/Significance

Our study shows neither QFT-G alone or in combination with TST can be used to exclude the suspicion of active TB disease. However, unlike TST, QFT-G yielded fewer false negative results even in individuals with low CD4 count. The low PHA cut-off point for indeterminate results suggested in this study (≤0.25 IU/ml) may improve the proportion of valid QFT-G results.

The impact of HIV infection and CD4 cell count on the performance of an interferon gamma release assay in patients with pulmonary tuberculosis

BACKGROUND

The performance of the tuberculosis specific Interferon Gamma Release Assays (IGRAs) has not been sufficiently documented in tuberculosis- and HIV-endemic settings. This study evaluated the sensitivity of the QuantiFERON TB-Gold In-Tube (QFT-IT) in patients with culture confirmed pulmonary tuberculosis (PTB) in a TB- and HIV-endemic population and the effect of HIV-infection and CD4 cell count on test performance.

METHODOLOGY/PRINCIPAL FINDINGS

161 patients with sputum culture confirmed PTB were subjected to HIV- and QFT-IT testing and measurement of CD4 cell count. The QFT-IT was positive in 74% (119/161; 95% CI: 67-81%). Sensitivity was higher in HIV-negative (75/93) than in HIV-positive (44/68) patients (81% vs. 65%, p = 0.02) and increased with CD4 cell count in HIV-positive patients (test for trend p = 0.03). 23 patients (14%) had an indeterminate result and this proportion decreased with increasing CD4 cell count in HIV-positive patients (test for trend p = 0.03). Low CD4 cell count (<300 cells/microl) did not account for all QFT-IT indeterminate nor all negative results. Sensitivity when excluding indeterminate results was 86% (95% CI: 81-92%) and did not differ between HIV-negative and HIV-positive patients (88 vs. 83%, p = 0.39).

CONCLUSIONS/SIGNIFICANCE

Sensitivity of the QFT-IT for diagnosing active PTB infection was reasonable when excluding indeterminate results and in HIV-negative patients. However, since the test missed more than 10% of patients, its potential as a rule-out test for active TB disease is limited. Furthermore, test performance is impaired by low CD4 cell count in HIV-positive patients and possibly by other factors as well in both HIV-positive and HIV-negative patients. This might limit the potential of the test in populations where HIV-infection is prevalent.