Utility of interferon-gamma ELISPOT assay responses in highly tuberculosis-exposed patients with advanced HIV infection in South Africa

Efficacy and Risk Factors of Interferon-Gamma Release Assays among HIV-Positive Individuals

Latent tuberculosis is prevalent in HIV-infected people and has an impact on the progression of AIDS. The aim of this study is to match a more accurate IGRA method for the better detection of latent tuberculosis infection in HIV patients. All 2394 patients enrolled were tested using three IGRA methods. The positive rate consistency of pairwise comparison and risk factors were analyzed. Receiver operator characteristic (ROC) curve analysis was applied to evaluate the diagnostic value of T-SPOTTB. The positive rates of the three methods were statistically different (p < 0.001). The CD4⁺ T cell number statistically impacted the QuantiFERON and Wan Tai tests after the analysis with univariate logistic regression, while no statistical difference was observed in T-SPOT.TB. Additionally, there was a better sensitivity and specificity of T-SPOT.TB if the positive cut-off value of ESAT-6 and CFP-10 was 4.5 and 5.5, respectively. This study provides an insight into the IGRA methods and demonstrated that the positive response detected via QuantiFERON declined with decreased CD4⁺ T cells in the HIV-infected population; T-SPOT.TB functions independently of the CD4⁺ T cell level and Wan Tai was affected in some cases. This will be useful in the diagnosis of LTBI in the HIV-infected population, which will be a key step toward TB elimination in China.

Relationship between T-SPOT.TB responses and numbers of circulating CD4+ T-cells in HIV infected patients with active tuberculosis

This study sought to evaluate the performance of the T-SPOT.TB assay for the diagnosis of active tuberculosis (TB) in human immunodeficiency virus (HIV) infected patients. One hundred confirmed HIV-infected patients with active TB and known T-SPOT.TB and CD4+ T-cell counts were enrolled in this clinical retrospective study. We found that patients with lower CD4+ T-cell counts (11-50 cells/μL) had the lowest T-SPOT.TB positive rates (50%), and patients with higher CD4+ T-cell counts (50-100 cells/μL) had the highest T-SPOT.TB positive rates (75%). However, there were no significant differences between the T-SPOT.TB positive rates of patients with different CD4+ T-cell counts (< 10, 11-50, 51-100 and > 100 cells/μL) (χ(2) = 3.7747, p = 0.287). The patients with positive TB culture results had significantly higher T-SPOT.TB positive rates (78.9%) than patients that were culture-negative (44.3%) (χ(2) = 12.8303, p < 0.001). Other variables, including gender, age, TB disease classification, HIV RNA level, and highly reactive antiretroviral therapy (HAART), had no significant effects on T-SPOT.TB positive rates. The number of spot-forming cells (SFCs) reactive with ESAT-6, CFP-10 and ESAT-6/CFP-10-specific T cells detected by T-SPOT.TB were positively is strongly related to the degree of immunodeficiency, while the T-SPOT.TB positive rates are less dependent on the level of CD4+ T-cell depletion in HIV infection and active TB.

A multicenter clinical evaluation of Mycobacterium tuberculosis IgG/IgM antibody detection using the colloidal gold method

A specific immunoassay method with the colloidal gold labeling technique has been developed more and more for tuberculosis (TB) diagnosis. The aim of this multicenter clinical evaluation was to evaluate the performance of a new serological diagnostic kit (the Trustline TB IgG/IgM Rapid Test kit) for the detection of Mycobacterium tuberculosis infection in China, with the Aupu TB Ab (IgG) Colloidal Gold Test kit being used as a control. A total of 1,009 specimens were collected from three TB hospitals, including 628 patients with TB, and 219 non-TB and 162 healthy patients as negative controls. According to the clinical diagnostic results, the sensitivities of the Trustline kit and the Aupu kit were 61.3 % and 53.7 %, respectively. Using the bacteriological test results as the "gold standard" to compare the results of the two kits, the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and Youden index (YI) were 77.60 %, 79.8 %, 73.31 %, 81.50 %, and 0.574 by the Trustline kit, and 67.86 %, 88.9 %, 83.27 %, 77.40 %, and 0.568 by the Aupu kit, respectively. Further, the sensitivity of the Trustline kit and the Aupu kit for the smear staining and the bacterial culture being positive was 75.6 %, 76.6 % and 65.6 %, 66.5 %, and for the negative result, it was 53.8 %, 50.9 % and 47.5 %, 45.0 %, respectively. Additionally, 35 specimens were IgM-positive by the Trustline kit; of these, 30 (4.8 %) were from patients with TB and 5 (1.3 %) were from individuals without TB. The results showed that the experimental test had a much higher sensitivity than the other commercial test and exhibited a good detection rate for M. tuberculosis infection. Therefore, this kit can be used in the supplementary diagnosis and screening of TB.

Serological diagnostic assays for HIV-associated tuberculosis in sub-Saharan Africa?

In this issue of Clinical and Vaccine Immunology, Siev and colleagues present an evaluation of antibody responses to four immunodominant proteins of Mycobacterium tuberculosis in patients with HIV-associated pulmonary tuberculosis (TB) in South Africa (M. Siev, D. Wilson, S. Kainth, V. O. Kasprowicz, C. M. Feintuch, E. Jenny-Avital, and J. J. Achkar, 21:791-798, 2014, doi:http://dx.doi.org/10.1128/CVI.00805-13). This commentary discusses the enormous need for simple point-of-care assays for tuberculosis (TB) diagnosis in patients with and without HIV coinfection in high-burden settings and considers the potential role of serological assays and the huge challenges inherent in developing and validating such assays.

Predictive value of interferon-γ ELISPOT assay in HIV 1-infected patients in an intermediate tuberculosis-endemic area

The tuberculin skin test for diagnosing latent tuberculosis (TB) has some limitations for HIV-infected patients, especially in BCG vaccinated countries. The objective of this study was to identify the incidence rate of new TB cases among HIV-infected patients in an intermediate TB-endemic area and to examine its correlation with the ELISPOT assay. We prospectively followed up 124 patients with HIV-1 infection to monitor development of active TB disease after performing an ELISPOT assay (T-SPOT. TB test, Oxford Immunotec, Ltd., Abingdon, UK). A total of 120 patients were followed for a median of 947 days; four patients with active TB at enrollment were excluded. Eleven patients developed active TB during 238 person-years, giving a high incidence rate of 4621/100,000 person-years. Patients with positive ELISPOT responses had a higher TB incidence rate than those with negative ELISPOT responses; however this was not statistically significant [20% (6/30) vs. 6.02% (5/83), p=0.052]. A Cox regression analysis showed that the independent risk factors associated with progression of TB were low CD4(+) T cell counts, previous history of TB treatment, and positive ELISPOT results. Advanced HIV-infected patients who showed a positive TB ELISPOT assay had a higher rate of progression to TB in the intermediate TB-endemic area.

Improving the diagnosis of tuberculosis: From QuantiFERON to new techniques to diagnose tuberculosis infections

The diagnosis of latent and active tuberculosis in the HIV-positive population is challenged by diminished sensitivity of conventional tests, atypical presentations, and the lack of culture methods in the developing world, where the burden of co-infection is greatest. In response to these challenges, a variety of new diagnostics have emerged. These include interferon-gamma release assays for the diagnosis of latent tuberculosis (TB) infection and novel culture methods and molecular assays for the diagnosis of active tuberculosis. Although some tests (such as interferon-gamma release assays) are not clearly superior to existing diagnostics, other novel diagnostics, such as real-time polymerase chain reaction and the microscopic observed direct susceptibility assay hold much promise for prompt and accurate TB diagnosis in this population. Line-probe, nitrate reductase, and mycobacteriophage assays have also provided rapid alternatives to conventional time-consuming drug susceptibility testing and are critical to curtailing the spread of multidrug-resistant TB.

Attenuated Listeria monocytogenes vaccine vectors expressing influenza A nucleoprotein: preclinical evaluation and oral inoculation of volunteers

Listeria monocytogenes vectors have shown promise for delivery of viral and tumor antigens in animals. We used two mutant vector strains deleted for actA/plcB (BMB72) and actA/inlB (BMB54), and engineered both strains to secrete a heterologous nucleoprotein antigen from the Influenza A virus. Strains were evaluated in vitro and in mice. Twenty-two healthy volunteers received single oral doses of either strain in a physiological study of safety, shedding, and immunogenicity. Volunteers were observed in the hospital for seven days and had daily blood cultures, routine safety blood tests (complete blood count with differential; hepatic and renal function), and fecal cultures; none had fever, positive blood cultures, prolonged shedding, or serious or unexpected events. Four of 12 volunteers who received the actA/plcB-deleted strain had minor, transient, asymptomatic serum transaminase elevations (maximum increase 1.4× upper normal). Six of six volunteers who received ≥4 × 10(9) colony forming units had detectable mucosal immune responses to listerial antigens, but not to the vectored influenza antigen. Approximately half the volunteers had modest interferon-γ ELISpot responses to a complex listerial antigen, but none had increases over their baseline responses to the influenza antigen. Comparison with prior work suggests that foreign antigen expression, and perhaps also freezing, may adversely affect the organisms' immunogenicity.

Methylated HBHA produced in M. smegmatis discriminates between active and non-active tuberculosis disease among RD1-responders

Background

A challenge in tuberculosis (TB) research is to develop a new immunological test that can help distinguish, among subjects responsive to QuantiFERON TB Gold In tube (QFT-IT), those who are able to control Mtb replication (remote LTBI, recent infection and past TB) from those who cannot (active TB disease). IFN-γ response to the Heparin-binding-hemagglutinin (HBHA) of Mtb has been associated with LTBI, but the cumbersome procedures of purifying the methylated and immunological active form of the protein from Mtb or M. bovis Bacillus Calmette et Guerin (BCG) have prevented its implementation in a diagnostic test. Therefore, the aim of the present study was to evaluate the IFN-γ response to methylated HBHA of Mtb produced in M. smegmatis (rHBHAms) in individuals at different stages of TB who scored positive to QFT-IT.

Methodology/Principal Findings

87 individuals at different stages of TB who scored positive to QFT-IT were selected. IFN-γ response to in vitro whole blood stimulation with rHBHAms was evaluated by short-term and long-term tests and detected by ELISA or flow cytometry. We demonstrated that the IFN-γ response to rHBHAms is mediated by CD4⁺ T-cells with an effector-memory phenotype. This response, evaluated by short-term-tests, is significantly lower in active TB than in remote LTBI (p = 0.0010) and past TB (p = 0.0152). These results were confirmed by long-term tests. The qualitative data confirmed that IFN-γ responses higher than the cut-off point identified by ROC analysis are associated with the status of non-active disease.

Conclusions

In this study we show that the T-cell response to a recombinant and methylated HBHA of Mtb produced in M. smegmatis is useful to discriminate between active and non-active TB disease among those responsive to QFT-IT in a whole blood system. Further studies are needed to improve the accuracy of the assay.

T-SPOT.TB in the diagnosis of active tuberculosis among HIV-infected patients with advanced immunodeficiency

We evaluated the performance of T-SPOT.TB (a commercial interferon gamma release assay) and its accuracy for the diagnosis of active tuberculosis (TB) among HIV-infected subjects with advanced immunodeficiency. In a clinical prospective study, we assessed the performance of T-SPOT.TB for the diagnosis of active TB in HIV-infected patients with CD4 cell counts below 350 cells/mm(3) who were naive to antiretroviral and anti-TB therapies. Results were available from 147 patients, of whom 38 (25.9%) had active TB. The majority (85%) of the participants were male, with a median age of 40 years and a median CD4 cell count of 77 cells/mm(3). T-SPOT.TB yielded 15 (10.2%) indeterminate results. The indeterminate results were not associated with CD4 cell counts. However, younger patients were more likely to have an indeterminate result (OR = 0.91 per unit increase in age, p = 0.007). After excluding the indeterminate results, the sensitivity of T-SPOT.TB for the diagnosis of active TB was 37.1% and the specificity was 88.7%. The sensitivity of the T-SPOT.TB was independent of the CD4 cell count. However, its specificity was higher when used for patients with CD4 cell counts <100 cells/mm(3) when compared to patients with CD4 cell counts ≥100 cells/mm(3) (97.9% vs. 79.6%, p = 0.008). T-SPOT.TB could not be used as a routine tool to screen for active TB among HIV-infected patients with advanced immunodeficiency because of its poor performance and low sensitivity. However, it may be used as an adjunctive tool to diagnose active TB in this population due to its high specificity.

Recent advances in testing for latent TB

After more than a century of relying on skin testing for the diagnosis of latent TB infection, clinicians now have access to blood-based diagnostics in the form of interferon γ release assays (IGRAs). These tests are generally associated with higher sensitivity and specificity for diagnosis of latent TB infection. This article reviews the indications for testing and treatment of latent TB infection in the overall context of a TB control program and describes how IGRAs might be used in specific clinical settings and populations, including people having close contact with an active case of TB, the foreign born, and health-care workers.

Interferon γ responses to mycobacterial antigens protect against subsequent HIV-associated tuberculosis

BACKGROUND

The cellular immune responses that protect against tuberculosis have not been identified.

METHODS

We assessed baseline interferon γ (IFN‐γ) and lymphocyte proliferation assay (LPA) responses to antigen 85 (Ag85), early secretory antigenic target 6 (ESAT‐6), and Mycobacterium tuberculosis whole cell lysate (WCL) in human immunodeficiency virus (HIV)-infected and bacille Calmette‐Guérin (BCG)-immunized adults with CD4 cell counts of >or= 200 cells/μL who received placebo in the DarDar tuberculosis vaccine trial in Tanzania. Subjects were followed prospectively to diagnose definite or probable tuberculosis.

RESULTS

Tuberculosis was diagnosed in 92 of 979 subjects during a mean follow‐up of 3.2 years. The relative risk of tuberculosis among subjects with positive IFN‐γ responses to Ag85 was 0.51 (95% confidence interval [CI], 0.26-0.99; P = .049), to ESAT‐6 was 0.44 (95% CI, 0.23-0.85; P = .004), and to WCL was 0.67 (95% CI, 0.49-0.88; P = .002). The relative risk of tuberculosis was not significantly associated with baseline LPA responses. In a multivariate Cox regression model, subjects with IFN‐γ responses to ESAT‐6 and WCL had a lower hazard of developing tuberculosis, with a hazard ratio for ESAT‐6 of 0.35 (95% CI, 0.16–0.77; P = .009) and a hazard ratio for WCL of 0.30 (95% CI, 0.16-0.56; P < .001).

CONCLUSIONS

Baseline IFN‐γ responses to ESAT-6 and WCL were associated with protection from subsequent tuberculosis among HIV-infected subjects with childhood BCG immunization in a region of high tuberculosis prevalence. Trial registration. ClinicalTrials.gov identifier: NCT00052195.

Is IP-10 an accurate marker for detecting M. tuberculosis-specific response in HIV-infected persons?

Background

The suboptimal sensitivity of Interferon (IFN)-γ-based in-vitro assays, especially in immunocompromised individuals, emphasizes the need for alternative markers for diagnosing tuberculosis (TB). The objective of this study was to evaluate whether interferon-inducible protein (IP)-10, monocyte chemotactic protein (MCP)-2 and interleukin (IL)-2 can be useful biomarkers for evaluating a specific response to RD1 antigens associated to active TB disease in HIV-infected individuals.

Methodology/Principal Findings

The study was carried out in India, the country with the highest TB burden in the world. Sixty-six HIV-infected individuals were prospectively enrolled, 28 with active-pulmonary-TB and 38 without. The whole blood assay based on RD1-selected peptides (experimental test) and QuantiFERON-TB Gold In tube (QFT-IT) was performed. Plasma was harvested at day-1-post-culture and soluble factors were evaluated by ELISA. The results indicate that by detecting IP-10, the sensitivity of the experimental test and QFT-antigen (75% and 85.7% respectively) for active TB was higher compared to the same assays based on IFN-γ (42.9% and 60.7% respectively) and was not influenced by the ability to respond to the mitogen. By detecting IP-10, the specificity of the experimental test and QFT-antigen (57.9% and 13.2% respectively) for active TB was lower than what was reported for the same assays using IFN-γ-detection (78.9% and 68.4% respectively). On the other side, in vitro IL-2 and MCP-2 responses were not significantly associated with active TB.

Conclusions

HIV infection does not impair RD1-specific response detected by IP-10, while it significantly decreases IFN-γ-mediated responses. At the moment it is unclear whether higher detection is related to higher sensitivity or lower specificity of the assay. Further studies in high and low TB endemic countries are needed to elucidate this.

IFN-gamma, but not IP-10, MCP-2 or IL-2 response to RD1 selected peptides associates to active tuberculosis

OBJECTIVES

To evaluate whether in vitro response to Mycobacterium tuberculosis RD1 peptides selected by computational analysis, measured by IFN-gamma, IP-10, MCP-2 or IL-2 production, is associated with active tuberculosis (TB) in a country with a high incidence of TB.

METHODS

129 individuals were prospectively enrolled, 41 with active-pulmonary TB and 88 without (household contacts and community controls). A whole blood assay based on RD1 selected peptides was performed. Soluble factors were evaluated by ELISA in plasma harvested at day1-post-culture. Enrolled individuals were also tested by QuantiFERON TB-Gold In tube (QFT-IT) and tuberculin skin tests (TST).

RESULTS

IFN-gamma response to RD1 selected peptides was significantly higher in active TB patients than in household contacts and community controls. IP-10 and MCP-2 response did not differ between active TB patients and household contacts, although it was higher in these groups compared to community controls; conversely IL-2 response did not differ among the three groups. When IFN-gamma response to RD1 selected peptides was scored based on receiver-operator-characteristic analysis, active TB was predicted with 68% sensitivity and 86% specificity. QFT-IT and TST showed a sensitivity for active TB of 90% and 68% and a specificity of 58% and 59%, respectively.

CONCLUSIONS

IFN-gamma (but not IP-10, MCP-2 and IL-2) response to RD1 selected peptides is associated with active TB with a higher specificity than QFT-IT and TST.

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

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

Changing prevalence of tuberculosis infection with increasing age in high-burden townships in South Africa

SETTING

Crowded townships of Cape Town, South Africa, where human immunodeficiency virus (HIV) prevalence and tuberculosis (TB) notification rates are among the highest in the world.

OBJECTIVES

To determine age-specific prevalence rates of latent tuberculosis infection (LTBI) among HIV-negative individuals, and the annual risk and force of infection during childhood and adolescence.

DESIGN

A cross-sectional survey using a standardised tuberculin skin test (TST) in HIV-negative individuals aged 5-40 years. A TST diameter of > or =10 mm was defined as indicative of LTBI.

RESULTS

Among 1061 individuals, only 4.7% had low-grade TST responses of 1-9 mm. However, the proportions of individuals with TST > or =10 mm increased from 28.0% in the 5-10 year age stratum to 88.0% in the 31-35 year age stratum. The mean annual risk of infection was 3.9% up to 5 years of age. The estimated force of infection (the rate of acquisition of LTBI among the residual pool of non-infected individuals) increased throughout childhood to a maximum of 7.9% per year at age 15 years.

CONCLUSIONS

Extremely high rates of infection in childhood and adolescence result in very high LTBI prevalence rates in young adults who are most at risk of acquiring HIV infection. This may be an important factor fuelling the high rates of HIV-associated TB in southern Africa.

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.

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

Background

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

Methods

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

Results

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

Conclusion

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

Is the QuantiFERON-TB blood assay a good replacement for the tuberculin skin test in tuberculosis screening? a pilot study at Berkshire Medical Center

The QuantiFERON-TB Gold In-Tube method (QFT-GIT; Cellestis, Carnegie, Australia) is a recently US Food and Drug Administration-approved interferon-gamma release assay (IGRA) for the detection of tuberculosis infection, which has been screened for by the tuberculin skin test (TST) for nearly a century. We report a pilot study comparing the QFT-GIT and TST results for screening health care workers (HCWs) at Berkshire Medical Center (BMC; Pittsfield, MA), the second hospital in Massachusetts to use QFT-GIT. For the study, 40 BMC HCWs, 20 TST+ and 20 TST-, were screened with the QFT-GIT test. All 20 TST- subjects were also QFT-GIT-, while only 10 of 20 TST+ subjects were QFT-GIT+. The overall agreement between the QFT-GIT and TST results was 75% (kappa = 0.5; 95% confidence interval, 0.268-0.732). The suboptimal agreement was partially due to a higher specificity of QFT-GIT. Confounding factors (eg, bacille Calmette-Guérin vaccination status and birthplace) are discussed, and literature regarding IGRAs and their comparison with TST is reviewed.

[Factors related to non-prescription of tuberculin skin testing in a cohort of HIV-infected people]

INTRODUCTION

Tuberculin skin testing (TST) for tuberculosis (TB) is recommended for all patients with HIV infection because of the known relationship between these two conditions. In this report we analyze the incidence and variables associated with non-prescription of TST in a cohort of HIV-infected people.

PATIENTS AND METHODS

Longitudinal study conducted between 2000 and 2002 at 10 HIV hospital-based clinics. All HIV-infected patients who had not been regularly followed-up previously in dedicated clinics were identified. Data about TST and other variables related to TB were obtained from the clinical records. We calculated the percentage of patients who did not undergo TST and the associated factors, using odds ratios (ORs) and the 95% CI to investigate associations. A multivariate logistic regression analysis was performed.

RESULTS

A total of 1242 patients met the inclusion criteria. TST was not performed in 185 patients (17.6% of those eligible). The fact of being an intravenous drug abuser was associated with a higher probability of TST non-prescription (OR: 2.6, 95% CI 1.1-6.5), whereas being unemployed (OR: 0.6, 95% CI 0.3-1.0), having a CD4 cell count >200 (CD4 200-499: OR 0.5, 95% CI 0.3-0.9. CD4> or =500: OR 0.3, 95% CI 0.2-0.6), and contact with persons with TB (OR 0.2, 95% CI 0.1-0.5) were associated with a lower probability.

CONCLUSIONS

In this study, the percentage of TST non-prescription was quite high. The results suggest that TST non-prescription in this population is related to the clinicians' expectations regarding the results of the test and the patients' adherence to treatment for latent TB infection.

Epidemiology of HIV-associated tuberculosis

PURPOSE OF REVIEW

We review literature concerning the epidemiology of HIV-associated tuberculosis (HIV-TB), focusing on articles published between 2007 and 2008.

RECENT FINDINGS

An estimated 1.37 million new cases of HIV-TB occurred in 2007, representing 15% of the total global burden of TB. In addition, an estimated 456 000 HIV-TB deaths accounted for 23% of global HIV/AIDS mortality. Sub-Saharan Africa is the worst affected region with 79% of the disease burden. The epicentre of the coepidemic lies in the south of the continent, with South Africa alone accounting for over one quarter of all cases. A critical overlap between HIV and the global multidrug-resistant TB epidemics is emerging. Although it is as yet unclear whether HIV is driving a disproportionate increase in multidrug-resistant TB cases at a population level, HIV has nevertheless been a potent risk factor for institutional outbreaks, especially in South Africa and eastern Europe. Increasing data have highlighted the risk of TB among HIV-infected healthcare workers in resource-limited settings. However, many studies also show the major benefits to be derived from antiretroviral therapy in high-income and low-income countries.

SUMMARY

HIV-TB remains a major challenge to global health that requires substantial increases in resource allocation and concerted international action.

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.

Detection of tuberculosis in HIV-infected children using an enzyme-linked immunospot assay

OBJECTIVE

To evaluate an enzyme-linked immunospot assay (ELISPOT) for the diagnosis of tuberculosis (TB) in HIV-infected children with suspected TB and to compare the performance of ELISPOT with the tuberculin skin test (TST).

METHODS

Interferon-gamma responses to Mycobacterium tuberculosis-specific antigens were measured by ELISPOT in HIV-infected children with suspected TB. HIV-infected and HIV-uninfected children without TB were taken for comparison.

RESULTS

Results were available for 188 children, of whom 139 (74%) were HIV-infected. Of these, 22 were classified as having definite TB: 24 probable TB, 14 possible TB and 128 not having TB. The median (range) age of patients was 20 (10-54.1) months. Median interferon-gamma responses to early-secreted antigenic target-6 and culture filtrate protein-10 were higher in children with definite or probable TB compared with children without TB (P < 0.002). In HIV-infected children with an interpretable ELISPOT result, the ELISPOT was positive in 14/21 (66%) with definite TB. A significantly higher proportion of HIV-infected children with definite or probable TB had a positive ELISPOT compared with a positive TST [25/39 (64%) vs. 10/34 (29%), P = 0.005]. In contrast to TST, results from ELISPOT were not affected by young age or severe immunosuppression. In HIV-infected children without active TB disease, 27% had a positive ELISPOT, suggesting latent TB infection.

CONCLUSION

ELISPOT is more sensitive than TST for the detection of active TB in HIV-infected children. However, the sensitivity of current ELISPOT assays is not sufficiently high to be used as a rule out test for TB.

MenA is a promising drug target for developing novel lead molecules to combat Mycobacterium tuberculosis

Potent inhibitors of MenA (1,4-dihydroxy-2-naphtoate prenyltrasferase) in Mycobacterium tuberculosis are identified, and are also effective in inhibiting growth of Mycobacterium tuberculosis at low concentrations. The MenA inhibitors possess common chemical structural features of (alkylamino)oalkoxyphenyl)(phenyl)methanones. Significantly, the MenA inhibitors can be synthesized in a few steps with high overall yields. The representative MenA inhibitors are highly effective in killing nonreplicating Mycobacterium tuberculosis that is evaluated by using the Wayne low oxygen model. In addition, a series of drug resistant Mycobacterium spp. are sensitive to the MenA inhibitors. The results are expected to be of significance in terms of discovering new lead compounds that can be developed into new drugs to combat unmet diseases caused by Mycobacterium tuberculosis.

New diagnostic methods for tuberculosis

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Lymphocyte proliferation to mycobacterial antigens is detectable across a spectrum of HIV-associated tuberculosis

Background

Identifying novel TB diagnostics is a major public health priority. We explored the diagnostic characteristics of antimycobacterial lymphocyte proliferation assays (LPA) in HIV-infected subjects with latent or active TB.

Methods

HIV-infected subjects with bacille Calmette Guérin (BCG) scars and CD4 counts ≥ 200 cells/mm³ entering a TB booster vaccine trial in Tanzania had baseline in vivo and in vitro immune tests performed: tuberculin skin tests (TST), LPA and five day assays of interferon gamma (IFN-γ) release. Assay antigens were early secreted antigenic target 6 (ESAT-6), antigen 85 (Ag85), and Mycobacterium tuberculosis whole cell lysate (WCL). Subjects were screened for active TB at enrollment by history, exam, sputum smear and culture. We compared antimycobacterial immune responses between subjects with and without latent or active TB at enrollment.

Results

Among 1885 subjects screened, 635 had latent TB and 13 had active TB. Subjects with latent TB were more likely than subjects without TB to have LPA responses to ESAT-6 (13.2% vs. 5.5%, P < 0.0001), Ag85 (18.7% vs. 3.1%, P < 0.0001), and WCL (45.7% vs. 17.1%, P < 0.0001). Subjects with active TB also were more likely than those without active TB to have detectable LPA responses to ESAT-6 (38.5% vs. 8.1%, P = 0.0001), Ag85 (46.2% vs. 8.5%, P < 0.0001), and WCL (61.5% vs. 27.0%, P = 0.0053). In subjects with a positive TST, LPA responses to ESAT-6, Ag85 and WCL were more common during active TB (p < 0.0001 for all tests). In diagnosing active TB, in vivo and in vitro tests of mycobacterial immune responses had sensitivity and specificity as follows: TST 84.6% and 65.5%, ESAT-6 LPA 38.5% and 92.0%, Ag85 LPA 46.2% and 91.5%, and WCL LPA 61.5% and 73.0%. Detectable LPA responses were more common in patients with higher CD4 counts, and higher HIV viral loads.

Conclusion

Lymphoproliferative responses to mycobacteria are detectable during HIV-associated active TB, and are less sensitive but more specific than TST.

Trial registration

ClinicalTrials.gov Identifier NCT00052195.

Comparing QuantiFERON-tuberculosis gold, T-SPOT tuberculosis and tuberculin skin test in HIV-infected individuals from a low prevalence tuberculosis country

OBJECTIVE

To evaluate the interferon-gamma-releasing assays QuantiFERON-tuberculosis (TB) Gold and T-SPOT.TB in addition to tuberculin skin test (TST) for diagnosis of latent tuberculosis infection in HIV patients.

DESIGN, SETTING AND PARTICIPANTS

Prospective cross-sectional study for asymptomatic HIV-infected outpatients from a large University hospital.

INTERVENTION

Simultaneous performance of QuantiFERON-TB Gold, T-SPOT.TB and TST.

MAIN OUTCOME MEASURES

Incidence and risk factors for a positive test reaction and the concordance (kappa) between the tests were investigated.

RESULTS

Of 286 enrolled patients, 81% were men; median age was 44 years, the median CD4 cell count 408/microl (range 7-1510) with a median nadir of 126/microl (range 0-749). A number of patients (63.8%) had undetectable HIV RNA (<50 copies/ml). Both T-SPOT.TB and QuantiFERON-TB showed more positive test results than TST: 25.2 and 20.0% (P = 0.133) compared with 12.8% (P < 0.001 and P = 0.008, respectively). Agreement between T-SPOT.TB and TST (kappa = 0.201) respectively QuantiFERON-TB and TST (kappa = 0.335) was fair, but only poor between the serological assays (kappa = 0.146). T-SPOT.TB provided more indeterminate results than QuantiFERON-TB (8 vs. 1/256, P < 0.01). Patients with a positive QuantiFERON-TB result had higher median CD4 cell counts (457 vs. 405 cells/microl for patients with negative result, P = 0.044); the amount of released interferon-gamma correlated with CD4 cell counts (rho = 0.199; P < 0.002). T-SPOT.TB results were independent from CD4 cell counts.

CONCLUSION

In HIV-infected patients from a low prevalence TB country, both interferon-gamma assays are more sensitive than TST, but seem to be less sensitive than in immunocompetent patients. The blood tests show poor agreement and differ in their dependence on the CD4 cell count.

Potent immune responses of Ag-specific Vgamma2Vdelta2+ T cells and CD8+ T cells associated with latent stage of Mycobacterium tuberculosis coinfection in HIV-1-infected humans

OBJECTIVE

To investigate immune responses of peptide-specific CD4+ and CD8+ T cells, and nonpeptide-specific Vgamma2Vdelta2+ T cells during clinical quiescence of latent Mycobacterium tuberculosis coinfection in HIV-1-infected humans.

METHODS

One hundred HIV-1-infected individuals who had HIV infection only [HIV+tuberculosis-(TB-)], latent Mycobacterium tuberculosis coinfection (HIV + LTB), or active tuberculosis (HIV + TB) were recruited to measure mycobacterium purified protein derivative (PPD)-specific IFNgamma+ CD4+ and CD8+ T cells, and phosphoantigen HMBPP-specific IFNgamma+ Vgamma2Vdelta2+ T cells using enzyme-linked immunospot and intracellular cytokine staining assays.

RESULTS

Both HIV + TB and HIV + LTB groups had low levels of PPD-specific IFNgamma+ CD4+ T cells regardless of CD4+ peripheral blood lymphocytes counts. However, numbers of PPD-specific IFNgamma+ CD8+ T cells in the HIV + LTB group were significantly greater than those in the HIV + TB group. Surprisingly, numbers of phosphoantigen hydroxy-3-methyl-but-2-enyl pyrophosphate-specific IFNgamma+ Vgamma2Vdelta2+ T cells in the HIV + LTB group were much greater than those in the HIV + TB group (P < 0.001). This difference was present in the subgroups of HIV + LTB whatever the levels of CD4+ T-cell counts more than 200/microl or less than 200/microl. Numbers of hydroxy-3-methyl-but-2-enyl pyrophosphate-specific IFNgamma+ Vgamma2Vdelta2+ T cells were even five times greater than those of PPD-specific IFNgamma+ CD8 T cells within the HIV + LTB group.

CONCLUSION

Potent immune responses of hydroxy-3-methyl-but-2-enyl pyrophosphate-specific IFNgamma+ Vgamma2Vdelta2+ T cells and PPD-specific IFNgamma+ CD8+ T cells were detected in HIV + LTB persons but not HIV + TB patients. The robust immune responses of Vgamma2Vdelta2+ and CD8+ T effector cells were associated with the latent stage of Mycobacterium tuberculosis coinfection in HIV-1-infected humans.

Rates of tuberculosis transmission to children and adolescents in a community with a high prevalence of HIV infection among adults

BACKGROUND

Tuberculin skin test surveys are routinely used to test for tuberculosis (TB) infection in communities, but there are few data from tuberculin skin test surveys from countries in which both TB and human immunodeficiency virus (HIV) infection are prevalent.

METHODS

We conducted a tuberculin skin test survey among 831 school-going children aged 5-17 years in a community that was experiencing an increase in the prevalence of TB and HIV infection. Responses to purified protein derivative RT23 were measured 3 days after the test was administered to determine tuberculin skin test results.

RESULTS

The prevalence of tuberculin skin test results positive for TB (i.e., an induration >or=10 mm in diameter in response to the skin test) ranged from 26.2% among children aged 5-8 years to 52.5% among children aged 14-17 years. The overall annual risk of infection was 4.1% using a 10-mm cutoff and 2.0% using a 17.4-mm cutoff. Annual risks of infection were constant across age groups. This is consistent with the finding that TB incidence remained the same in children (P= .48) from 1999 through 2005, although total TB incidence and adult TB (determined by sputum smear test) incidence increased in this community during the same period (P<.001).

CONCLUSIONS

The annual risk of infection is high in the community. It appears that HIV infection-associated TB is not a major influence on the annual risk of infection and that TB transmission from adults to children may be associated with a subset of TB cases in the community. An improved understanding of TB transmission patterns is urgently needed help the implementation of novel strategies for reducing the annual risk of infection in this setting.

Proposed management of childhood tuberculosis in low-incidence countries

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

Diagnosing latent tuberculosis infection in the HIV era

Tuberculin skin testing (TST) and Interferon-gamma (IFNγ)release assays (IGRAs) are presently the only available assays for the detection of Mycobacterium tuberculosis infected individuals. IGRAs might progressively replace TST, as numerous published reports establish their higher specificity and similar sensitivity when tested in BCG vaccinated, immunocompetent individuals or in populations who may have been in contact with atypical mycobacteria. However, few published reports have commented on their role in TB diagnosis in immunocompromised individuals (HIV, immunosuppressive therapy, cancer…). It is the purpose of this report to review IGRAs published studies in HIV individuals in endemic and non endemic area for tuberculosis (TB). IGRAs were tested in the presence or absence of active TB but correlated to duration of exposure. In newly diagnosed active TB, IGRAs demonstrated a similar sensitivity to TST. In TB non infected individuals, TST and IGRAs also gave similar values when categorization of individuals was correlated to the risk of infection. A higher number of positive IGRAs was observed in individuals from TB endemic areas, in similar proportions to immunocompetent individuals. Comparison between the two IGRAs: QuantiFERON-TB Gold^® (QF-TB, Cellestis, Australia) and T-SPOT-TB^® (Oxford Immunotec, UK), and against TST, in the same HIV population demonstrates a higher sensitivity of T-SPOT-TB and TST than QF-TB. Indeterminate results, which correspond to the absence of a positive T-cell IFNγ response towards phytohemaglutinin (PHA), is a key point when comparing both IGRAs. This PHA control is indicative of the level of immunosuppression observed in the tested individual. QF-TB seems to present, in HIV populations, more indeterminate results than T-SPOT-TB. The calibration and/or concentration of PBMC on nitrocellulose membrane for the T-SPOT-TB, as compared to a whole blood assay, might explain this difference, with less indeterminate results with the T-SPOT-TB assay. Neither assay is able to differentiate active TB from latent TB infection (LTBI). Several laboratories have tried new antigenic epitopes to solve this issue. It is of importance that these studies need to be repeated on a larger scale by others to validate their results. Two blood assays might add information characterising the evolution from LTBI to active TB: either by losing protective immunity, as demonstrated by the whole blood killing assay, or by evaluating the kinetics of the antibodies synthesized against M. tuberculosis specific antigens. In conclusion, longitudinal studies are still needed to validate IGRAs and other assays and to define their respective predictive values.

Detection of polyfunctional Mycobacterium tuberculosis-specific T cells and association with viral load in HIV-1-infected persons

BACKGROUND

The human immunodeficiency virus type 1 (HIV-1) epidemic is associated with a significant increase in the incidence of tuberculosis (TB); however, little is known about the quality of Mycobacterium tuberculosis (MTB)-specific cellular immune responses in coinfected individuals.

METHODS

A total of 137 HIV-1-positive individuals in Durban, South Africa, were screened with the use of overlapping peptides spanning Ag85A, culture filtrate protein 10 (CFP-10), early secretory antigen target 6 (ESAT-6), and TB10.4, in an interferon (IFN)-gamma enzyme-linked immunospot (ELISPOT) assay. Intracellular cytokine staining for MTB-specific production of IFN-gamma, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-2 was performed, as was ex vivo phenotyping of memory markers on MTB-specific T cells.

RESULTS

A total of 41% of subjects responded to ESAT-6 and/or CFP-10, indicating the presence of latent MTB infection. The proportion of MTB-specific IFN-gamma(+)/TNF-alpha(+) CD4(+) cells was significantly higher than the proportion of IFN-gamma(+)/IL-2(+) CD4(+) cells (P = .0220), and the proportion of MTB-specific IL-2-secreting CD4 cells was inversely correlated with the HIV-1 load (P = .0098). MTB-specific CD8 T cells were predominately IFN-gamma(+)/TNF-alpha(+)/IL-2(-). Ex vivo memory phenotyping of MTB-specific CD4 and CD8 T cells indicated an early to intermediate differentiated phenotype for the population of effector memory cells.

CONCLUSIONS

Polyfunctional MTB-specific CD4 and CD8 T cell responses are maintained in the peripheral blood of HIV-1-positive individuals, in the absence of active disease, and the functional capacity of these responses is affected by HIV-1 disease status.

Evaluation of a model for efficient screening of tuberculosis contact subjects

RATIONALE

Contact tracing is an important component of tuberculosis (TB) control programs. Standardization of contact investigation protocols can make them more efficient.

OBJECTIVES

To develop a model to select contact subjects for screening.

METHODS

We prospectively collected standardized data on 325 TB index cases and their 2,009 contacts. Factors that independently influenced the risk of TB infection were included in the model, which was then validated in a second prospective cohort of 88 cases of TB and their 618 contacts.

MEASUREMENTS AND MAIN RESULTS

A total of eight independent risk factors were identified (odds ratio; 95% confidence interval): age, with three subgroups: 6-14 years (3.6; 1.6-8.0); 15-29 years (3.7; 1.8-7.7); > or =30 years (4.1; 2.0-8.5); cavitation on the index case's chest radiograph (1.6; 1.1-2.2); an index case sputum smear with 100 or more acid-fast bacilli per field (1.8; 1.2-2.8); household contact at night (2.1; 1.3-3.2); first-degree family relationship with the index case (2.1; 1.3-3.3); active smoking by the contact (1.6; 1.1-2.4); free health care (2.0; 1.2-3.2); and birth in a country with TB incidence rate higher than 25 of 100,000 (2.2; 1.5-3.2). Predictive probabilities were chosen to ensure false-negative rates lower than estimated TB infection background. The number of contacts to be investigated was reduced by 26% while maintaining a false-negative rate of 8%.

CONCLUSIONS

This study provides a standardized contact screening model which reduces resources required without negatively affecting disease control.