Tuberculin Skin Test Response Research Articles

The tuberculin skin test in school going adolescents in South India: associations of socio-demographic and clinical characteristics with TST positivity and non-response.

BackgroundIndia has generally used 1 TU purified protein derivative (PPD) as opposed to 2 TU PPD globally, limiting comparisons. It is important to assess latent TB infection in adolescents given that they may be a target group for new post-exposure TB vaccines.The aim of this study is to describe the pattern and associations of tuberculin skin test (TST) responses (0.1 ml 2 TU) in adolescents in South India.Methods6643 school-going adolescents (11 to <18 years) underwent TST. Trained tuberculin reader made the reading visit between 48 and 96 hours after the skin testResultsOf 6608 available TST results, 9% had 0 mm, and 12% ≥10 mm responses. The proportion of TST positive (≥10 mm) was higher among older children, boys, those with a history of TB contact and reported BCG immunization Those with no TST response (0 mm) included younger participants (<14 years), those whose mothers were illiterate and those with a recent history of weight loss. Those of a higher socio-economic status (houses with brick walls, LPG gas as cooking fuel) and those with a visible BCG scar were less likely to be non-responders.ConclusionProportion of non-responders was lower than elsewhere in the world. Proportion of TST positivity was higher in those already exposed to TB and in children who had been BCG immunized, with a zero response more likely in younger adolescents and those with recent weight loss.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-014-0571-7) contains supplementary material, which is available to authorized users.

Association between HLA-DR4 haplotypes and tuberculin skin test response in the Aché population.

The human leukocyte antigen (HLA) system has a major role in the regulation of the immune response as it is involved in the defense against pathogens. Evidence for association with tuberculosis (TB) is more consistent for class II than for class I HLA genes. TB is important among indigenous peoples in South America, not only because of its historical role in regional depopulation, but also because it is still widespread. The aim of this study was to evaluate the association of HLA class II alleles, haplotypes and genotypes and tuberculin skin test response (TST) in 76 individuals of the Aché population. Poisson Regression was employed to assess risk genotypes. DRB1*04, DQA1*03 and DQB1*03:02 were associated with TST response in this population.

The frequencies of IFNγ+IL2+TNFα+ PPD-specific CD4+CD45RO+ T-cells correlate with the magnitude of the QuantiFERON® gold in-tube response in a prospective study of healthy indian adolescents.

BackgroundQuantiFERON-TB Gold In-Tube (QFT) is an IFNγ-release assay used in the diagnosis of Mycobacterium tuberculosis (MTB) infection. The risk of TB progression increases with the magnitude of the MTB-specific IFNγ-response. QFT reversion, also associated with low Tuberculin Skin Test responses, may therefore represent a transient immune response with control of M. tuberculosis infection. However, studies at the single cell level have suggested that the quality (polyfunctionality) of the T-cell response is more important than the quantity of cytokines produced.ObjectiveTo explore the quality and/or magnitude of mycobacteria-specific T-cell responses associated with QFT reversion and persistent QFT-positivity.MethodsMulti-color flowcytometry on prospectively collected peripheral blood mononuclear cells was applied to assess mycobacteria-specific T-cell responses in 42 QFT positive Indian adolescents of whom 21 became QFT negative (reverters) within one year. Ten QFT consistent negatives were also included as controls.ResultsThere was no difference in the qualitative PPD-specific CD4+ T-cell response between QFT consistent positives and reverters. However, compared with QFT consistent positives, reverters displayed lower absolute frequencies of polyfunctional (IFNγ+IL2+TNFα+) CD4+ T-cells at baseline, which were further reduced to the point where they were not different to QFT negative controls one year later. Moreover, absolute frequencies of these cells correlated well with the magnitude of the QFT-response.ConclusionWhereas specific polyfunctional CD4+ T-cells have been suggested to protect against TB progression, our data do not support that higher relative or absolute frequencies of PPD-specific polyfunctional CD4+ T-cells in peripheral blood can explain the reduced risk of TB progression observed in QFT reverters. On the contrary, absolute frequencies of these cells correlated with the QFT-response, suggesting that this readout reflects antigenic load.

Tuberculin Skin Test Distribution following a Change in BCG Vaccination Policy

BackgroundEpidemiologic data regarding tuberculin skin test (TST) responses are an important basis for TB control strategies. This study analyzed TST responses in Korea, which experienced a rapid change in BCG vaccination status.MethodsTST responses in young adults were examined over 5 years. Participants with active TB lesions were excluded.ResultsA total of 5,552 participants were enrolled with median age of 21 years. When an induration diameter ≥10 mm was used as the criterion for a positive test, TST positivity fell (from 28.0% in 2005 to 15.3% in 2009); however, they remained steady when the criterion was ≥15–20 mm. A positive TST was associated with a personal or family of TB, the presence of a Bacille Calmette-Guérin (BCG) scar, and age (odds ratio [95% confidence interval] = 4.03 [2.61–6.22], 2.91 [1.80–4.71], 1.50 [1.31–1.72], and 1.15 [1.09–1.20], respectively). Among these factors, the decrease of participants with BCG scars was the most prominent change, which appeared to be associated with the change of TST positivity rate.ConclusionOverall, the rate of TST positivity in Korea decreased. However, this trend seems associated with the change of BCG vaccination strategy rather than successful control of LTBI. This study showed that change in BCG vaccination strategy can have great impact on TB epidemiologic survey based on TST.

Prevelence of latent tuberculosis and associated risk factors in children under 5 years of age in Karachi, Pakistan

Background: As infected children represent a large proportion of the pool from which tuberculosis (TB) cases will arise and its associated risk factors that influence TB infection are basic cause for burden of TB. Aim: This study was to determine the prevalence of latent TB and associated risk factors in children less than 5 year of age in Karachi, Pakistan. Setting and Design: Cross-sectional study and it was conducted in tertiary care hospital in Karachi. Materials and Methods: In this study, children who were living in contact with individuals who had proven smear-positive pulmonary TB cases were investigated. A tuberculin skin test (TST) was performed on each child. TST sizes ≥5 and 10 mm, respectively, were considered positive. Statistical Analysis: A random effects logistic regression model, which takes into account the clustering of contacts within households, was used to assess the relationship between the tuberculin response of the contact and risk factors. Results are reported as unadjusted and adjusted odds ratios and their 95% confidence intervals. The likelihood ratio test was used to assess the overall significance of risk factors, tests for trend, and tests for interaction. Results: The distribution of TST responses followed a bimodal pattern, with 135 (35%) children presenting a palpable induration. The risk of positive TST response in the child increased with the geographic proximity of the child to the individual with TB within the household and with the degree of activities shared with the individual with TB. Nutritional status and presence of a bacille Calmette-Guérin (BCG) scar were not independent risk factors for TST positivity in this population. On multivariate analysis, the effect of geographic proximity to the individual with TB, household size, and duration of cough in the index case persisted for TST responses ≥5 mm. Conclusions: Positive TST in a child reflects most probably TB infection rather than previous BCG vaccination. Contact tracing can play a major role in the control of TB in Pakistan.

Evaluation of Tuberculin Skin Test Response and Interfering Factors in Patients with Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) is the most common rheumatologic disease in pediatric age group. Mycobacterium tuberculosis infection (TB) is an important cause of mortality and morbidity in patients with inflammatory rheumatologic disease. The objective of this study is to determine to what extent active disease and use of drugs in JIA affects response to PPD skin test and thus to investigate the significance of PPD skin test in the diagnosis of latent TB. 77 children diagnosed with JIA according to ILAR diagnostic criteria and routinely followed by our rheumatology clinic were included in the patient group. Patients were grouped according to subtypes of disease, activity status and drugs they used. Control group was formed from 58 healthy children. PPD skin test was applied to each subject and the number of BCG scars of all cases was recorded. We found no significant difference in PPD induration diameters between JIA and control group (p > 0.05). The number of BCG scar is similar in both groups. In the control group, age and number of BCG scars and PPD skin test diameter are positively correlated. But there is no such significant relationship in patients with JIA (p > 0.05). PPD induration diameter of patients with active disease is significantly shorter than patients in remission (p > 0.05). PPD induration diameter of patients treated with steroid and disease modifying anti-rheumatic drug (DMARD) and underwent remission were not significantly different from the control group. When compared with patients using other drugs, patients on remission using steroid and DMARD have shorter PPD induration diameter. Activity of disease and drugs used (steroid, DMARD) affects PPD response. In the diagnosis of latent TB, normal range of PPD diameter in healthy child changes in JIA patient with active disease. That the PPD diameter is shorter than normal range could indicate underlying TB infection. This fact should be considered in the follow-up of the patients with JIA.

Use of tuberculin skin test, IFN-γ release assays and IFN-γ-induced protein-10 to identify children with TB infection

Current tests of tuberculosis (TB) infection (tuberculin skin test (TST), interferon (IFN)-γ-release assays (IGRAs) and IFN-γ-induced protein (IP)-10) have limitations and their value when used consecutively to identify infected children has not been explored. This study describes TST, IGRA and IP-10 responses in children in contact with adults with TB, the agreement of the tests and whether using multiple tests indentifies more infected children. 330 children (aged 1-15 yrs) in contact with adults with pulmonary TB and 156 controls were studied in Ethiopia. Children exposed to adults with high bacilli grades in sputum were more likely to have positive TST, IFN-γ and IP-10 than controls. The agreement of positive tests was directly associated with the sputum bacilli grades (p<0.001 for all). The agreement of negative tests was higher in control children. The consecutive use of the tests increased the number of children classified as having at least one positive test. Using three tests increases the number of children classified as infected. This increase is associated with the bacilli load of the adults. Using only one test may underestimate the proportion of infected children, but the interpretation of the data is difficult due to the lack of reference standards.

Effect of Ascaris Lumbricoides specific IgE on tuberculin skin test responses in children in a high-burden setting: a cross-sectional community-based study.

BackgroundM.tuberculosis (M.tb) is associated with enhanced T helper cell type 1 (Th1) immune responses while helminth infection is associated with T helper cell type 2 (Th2) immune responses. Our aim was to investigate whether helminth infection could influence the ability to generate an appropriate Th1 immune response that is characterized by a positive tuberculin skin test (TST), in M.tb exposed children.MethodsWe completed a community-based, cross sectional household contact tracing study, using matched enrolment of HIV negative children with and without documented household M.tb exposure. We documented demographics, clinical characteristics, HIV status, M.tb exposure (using a standard contact score) and M.tb infection status (TST > = 10 mm). Ascaris lumbricoides-specific IgE was used as proxy for Ascaris infection/exposure.ResultsOf 271 children (median age 4 years (range: 4 months to 15 years)) enrolled, 65 participants (24%) were serum positive for Ascaris IgE. There were 168 (62%) children with a documented household tuberculosis contact and 107 (40%) were (TST) positive overall.A positive TST was associated with increasing age (Odds Ratio (OR) =1.17, p < 0.001), increasing M.tb contact score (OR = 1.17, p < 0.001), previous tuberculosis treatment (OR = 4.8, p = 0.06) and previous isoniazid preventive treatment (OR = 3.16, p = 0.01). A visible bacillus Calmette-Guérin (BCG) scar was associated with reduced odds of being TST positive (OR = 0.42, p = 0.01).Ascaris IgE was not associated with TST status in univariate analysis (OR = 0.9, p = 0.6), but multivariable logistic regression analysis suggested an inverse association between Ascaris IgE status and a positive TST (OR = 0.6, p = 0.08), when adjusted for age, and M.tb contact score. The addition of an age interaction term to the model suggested that the age effect was stronger among Ascaris IgE positive children; the effect of being Ascaris IgE positive significantly reduced the odds of being TST positive amongst younger children while this effect weakened with increasing age.ConclusionsOur preliminary findings highlight a high prevalence of both Ascaris exposure/infection and M.tb infection in children in an urban setting. Helminth exposure/infection may reduce the immune response following M.tb exposure when controlling for epidemiological and clinical covariates. These findings might be relevant to the interpretation of immunological tests of M.tb infection in children.

Influence of HTLV-1 on the clinical, microbiologic and immunologic presentation of tuberculosis

BackgroundHTLV-1 is associated with increased susceptibility to Mycobacterium tuberculosis infection and severity of tuberculosis. Although previous studies have shown that HTLV-1 infected individuals have a low frequency of positive tuberculin skin test (TST) and decreasing in lymphoproliferative responses compared to HTLV-1 uninfected persons, these studies were not performed in individuals with history of tuberculosis or evidence of M. tuberculosis infection. Therefore the reasons why HTLV-1 infection increases susceptibility to infection and severity of tuberculosis are not understood.The aim of this study was to evaluate how HTLV-1 may influence the clinical, bacteriologic and immunologic presentation of tuberculosis.MethodsThe study prospectively enrolled and followed 13 new cases of tuberculosis associated with HTLV-1 (cases) and 25 patients with tuberculosis without HTLV-1 infection (controls). Clinical findings, bacterial load in the sputum, x-rays, immunological response and death were compared in the two groups.ResultsThere were no differences in the demographic, clinical and TST response between the two study groups. IFN-γ and TNF-α production was higher in unstimulated cultures of mononuclear cells of case than in control patients (p < 0.01). While there was no difference in IFN-γ production in PPD stimulated cultures, TNF-α levels were lower in cases than in controls (p = 0.01). There was no difference in the bacterial load among the groups but sputum smear microscopy results became negative faster in cases than in controls. Death only occurred in two co-infected patients.ConclusionWhile the increased susceptibility for tuberculosis infection in HTLV-1 infected subjects may be related to impairment in TNF-α production, the severity of tuberculosis in co-infected patients may be due to the enhancement of the Th1 inflammatory response, rather than in their decreased ability to control bacterial growth.

Value of the tuberculin skin testing and of an interferon-gamma release assay in haemodialysis patients after exposure to M. tuberculosis

BackgroundPatients with end-stage renal disease (ESRD) and Mycobacterium tuberculosis infection pose a high risk of developing active TB disease. It is therefore important to detect latent TB infection (LTBI) to be able to offer treatment and prevent progression to TB disease. We assessed the value of the tuberculin skin test (TST) and of an interferon-gamma release assay (Quantiferon®-TB Gold in-Tube, QFT) for diagnosing LTBI in ESRD patients, after prolonged exposure to a highly contagious TB case in a haemodialysis unit. As a high number of patients presented erythema without induration in the TST response, this type of reaction was also analysed.MethodThe TST and QFT were simultaneously performed twelve weeks after the last possible exposure to a bacilliferous TB patient. If the first TST (TST-1) was negative, a second TST (TST-2) was performed 15 days later to detect a booster response. A comparison was made between the TST responses (including those cases with erythema without induration) and those for the QFT. The correlation with risk of infection and the concordance between tests were both analysed.ResultsA total of 52 patients fulfilled the inclusion criteria. Overall, 11 patients (21.2%) had a positive TST response: 3 for TST-1 and 8 for TST-2, and 18 patients (34.6%) showed a positive QFT response (p = 0.065). Erythema without induration was found in 3 patients at TST-1 and in a further 9 patients at TST-2. The three patients with erythema without induration in TST-1 had a positive TST-2 response. Concordance between TST and QFT was weak for TST-1 (κ = 0.21); it was moderate for overall TST (κ = 0.49); and it was strong if both induration and erythema (κ = 0.67) were considered.ConclusionsIn patients with ESRD, erythema without induration in the TST response could potentially be an indicator of M. tuberculosis infection. The QFT shows better accuracy for LTBI diagnosis than the TST.

The Affecting Factors and Comparison of Tuberculin Skin Test in Peritoneal Dialysis and Hemodialysis Patients

Compared with the general population, patients with chronic renal failure have increased tuberculosis (TB) prevalence and mortality rates. In this study, we aimed to investigate tuberculin skin test (TST) positivity rates in hemodialysis (HD) and peritoneal dialysis (PD) patients and the factors influencing TST positivity. Ninety-two HD patients and 44 PD patients who had been on HD and PD treatment for at least 3 months were recruited into the study. TST was administered in all patients. Positivity was defined as an induration diameter >10 mm. At least 5 mm of induration following skin testing together with a chest radiography indicating previous infection was defined as latent TB infection. TST positivity rates, diameter of TST indurations, and serum albumin levels in HD patients were higher than the PD patients. TST induration size was not correlated with any other parameters in both HD and PD groups. TST-positive patients had higher albumin levels and lower leukocyte count than the TST-negative patients. In TST-positive patients, albumin level was correlated with the duration of dialysis but TST induration size was not correlated with the lymphocyte count and albumin level. In our study, TST positivity of patients was found in 30.4% of HD patients, 9% of PD patients, and 23.5% of total patients. It is still recommended to use TST for the screening test of TB. We found a significant relationship between TST and albumin level. It should be remembered that TST response may be lower in PD patients, especially in cases in which TB is suspected.

Lack of correlation between BCG-induced tuberculin skin test sensitisation and protective immunity in cattle

Vaccination of cattle with Mycobacterium bovis Bacille Calmette-Guérin (BCG) can provide significant protection against bovine tuberculosis (TB). However, BCG vaccination sensitises animals to respond to the tuberculin skin-test. This provides a potential operational impediment to the use of BCG as a cattle vaccine since the tuberculin skin-test is the primary surveillance tool used by many countries with ‘test and slaughter’ control strategies. Currently, it is also unclear what BCG-induced skin-test conversion means in respects to BCG's protective immunity. In the current study we first investigated the duration of tuberculin skin-test sensitisation in calves neonatally vaccinated with BCG. BCG vaccination induced strong skin-test responses in calves during their first 6 months. However, a rapid decay in skin-test sensitivity was observed after this time. Between 6 and 9 months this represented a reduction from 80% to 8% of calves providing a positive response in the single intradermal comparative cervical tuberculin test at standard interpretation. We next investigated the relationship between BCG induced skin-test sensitivity and retention of protective immunity. Calves were neonatally vaccinated with BCG and subsequently divided into 2 groups based on retention or loss of tuberculin skin-test responses after 6 months. In contrast to their skin-test responsiveness, these vaccinates maintained their tuberculin specific IFN-γ blood responses. Moreover, irrespective of their pre-challenge skin-test responses, following M. bovis challenge both groups of BCG vaccinated calves demonstrated comparable levels of protection, as evidenced by reduced TB-associated pathology. Therefore, we have demonstrated that following neonatal BCG vaccination of cattle, tuberculin skin-test responder frequencies waned rapidly after 6 months but importantly, loss of skin-test sensitivity did not correlate with loss of protective immunity. These findings could have implications for the practical application of BCG based cattle vaccines.

Force of tuberculosis infection among adolescents in a high HIV and TB prevalence community: a cross-sectional observation study

BackgroundUnderstanding of the transmission dynamics of tuberculosis (TB) in high TB and HIV prevalent settings is required in order to develop effective intervention strategies for TB control. However, there are little data assessing incidence of TB infection in adolescents in these settings.MethodsWe performed a tuberculin skin test (TST) and HIV survey among secondary school learners in a high HIV and TB prevalence community. TST responses to purified protein derivative RT23 were read after 3 days. HIV-infection was assessed using Orasure® collection device and ELISA testing. The results of the HIV-uninfected participants were combined with those from previous surveys among primary school learners in the same community, and force of TB infection was calculated by age.ResultsThe age of 820 secondary school participants ranged from 13 to 22 years. 159 participants had participated in the primary school surveys. At a 10 mm cut-off, prevalence of TB infection among HIV-uninfected and first time participants, was 54% (n = 334/620). HIV prevalence was 5% (n = 40/816). HIV infection was not significantly associated with TST positivity (p = 0.07). In the combined survey dataset, TB prevalence was 45% (n = 645/1451), and was associated with increasing age and male gender. Force of infection increased with age, from 3% to 7.3% in adolescents ≥20 years of age.ConclusionsWe show a high force of infection among adolescents, positively associated with increasing age. We postulate this is due to increased social contact with infectious TB cases. Control of the TB epidemic in this setting will require reducing the force of infection.

Performance of tuberculin skin test and interferon gamma assay for the diagnosis of latent tuberculosis infection in juvenile idiopathic arthritis

The objective of this prospective cross-sectional study was to compare a Mycobacterium tuberculosis-specific interferon gamma (IFN-γ) enzyme linked immunosorbent assay [QuantiFERON-TB Gold In-Tube (QFT-GIT)] test with tuberculin skin test (TST) for detection of latent tuberculosis infection (LTBI) in patients with juvenile idiopathic arthritis (JIA). To our knowledge, this is the first study evaluating the performance of QFT-GIT in comparison with TST in JIA. A cross-sectional study of 39 children with JIA and 40 healthy controls was conducted in İzmir, Turkey. Blood was for drawn for the QFT-GIT assay prior to administration of the TST using 5 tubercullin units (TU) of purified protein derivative (PPD-S). A positive TST was defined as ≥10mm for JIA and ≥15mm for controls. Statistical analysis was performed using SPSS version 16.0 for Windows. There were no significant differences between JIA patients and controls for age, sex, and Bacillus Calmette-Guérin (BCG) vaccination. Of patients, 70% had active JIA disease. The median TST induration was 5.8mm (±5.7mm) for JIA and 10.7mm (±4.5mm) for the control group, which was statistically significant (p = 0.000). The rate of patients who showed no reaction to TST was 38%, of which 93% had active disease. There were two patients who had positive IFN-γ results but negative TST, who had systemic and polyarticular type JIA, respectively. Overall agreement between TST and QFT-GIT was low both in JIA and control group (κ value =0.06 and 0.10, respectively). TST may be inadequate to diagnose LTBI in JIA patients. The IFN-γ assay may be useful to identify false negative TST response in cases with latent M. tuberculosis infection. The combination of IF QFT-GIT method with TST would provide successful diagnostic screening for LTBI in JIA, particularly prior to anti-tumor necrosis factor treatment. Long-term prospective studies are still necessary to appreciate the advantages and the applicability of these tests in pediatrics.

Evaluation of an IFN-gamma Assay in the Diagnosis of Latent Tuberculosis in Patients with Psoriasis in a Highly Endemic Setting

Screening for latent tuberculosis infection is mandatory before starting anti-tumour necrosis factor treatments, but its diagnosis still poses a challenge. While studies performed in developed countries have demonstrated superior performance of T-cell based interferon-γ release assay (IGRA) compared with the tuberculin skin test, there is a debate about whether this holds true in tuberculosis endemic areas. The performance of an IGRA kit T-SPOT.TB was evaluated in 33 moderate-to-severe untreated psoriasis patients and, as controls, 30 patients with common dermatological diseases at a tuberculosis highly endemic setting. The frequency of positive tuberculin skin test responses and induration size in controls were higher than in psoriasis patients (53% vs. 18% and 9.3 ± 1.4 vs. 2.6 ± 0.7 mm, respectively, p < 0.001). In contrast, the frequency of positive response and mean number of spots elicited with the T-SPOT.TB test were not significantly different between patients and controls (47% vs. 43% and 14.7 ± 3.2 vs. 20.5 ± 3.1 spots/well, respectively). The two tests presented good agreement in the control, but not the psoriasis group (κ values of 0.625 and 0.375, respectively). Thus, in a highly tuberculosis-endemic setting the T-SPOT.TB test was superior to the tuberculin skin test in diagnosing latent tuberculosis infection in psoriasis, probably because the immune dysregulation of psoriasis shows a lower interference in the in vitro test.

181 Interferon-γ, Interferon-γ-Inducible Protein-10 and Tuberculin Skin Test Responses of Hiv-Positive and Hiv Negative Children in Northeast Brazil

Background and aims: Detection of latent tuberculosis (TB) infection (LTBI) and provision of chemoprophylaxis is an important strategy for TB control, particularly for HIV-infected children. Assessing LTBI in this population is difficult because the tuberculin skin test (TST) is unreliable in immunosuppressed individuals. Interferon-γ release assays (QTF) have been recently used as complementary tools for the diagnosis of LTBI and Interferon-γ inducible protein-10 (IP-10) has been evaluated as a potential marker for detection of Mycobacterium tuberculosis infection. Our aim was to describe Interferon-γ, IP-10 and TST responses in HIV-positive and negative children in Northeast Brazil. Methods: TST, Interferon-γ and IP-10 responses were evaluated in HIV-positive and HIV-negative children with known contact with adults with TB, a previous or current diagnosis of active TB and controls with no history of TB contact or disease. Results: 41 HIV-positive and 56 HIV-negative children were enrolled. The concordance of TST and QTF was high amongst HIV-positive and HIV-negative children (k 0.85 and k 0.82 respectively). IP-10 concentrations were higher for both HIV-positive and negative children with positive QTF/TST agreement. HIV-positive children had lower IP-10 concentrations when compared with HIV-negative children. Interferon-γ and IP-10 concentrations did not significantly differ amongst HIV-positive children with active TB, TB Contact or controls. Among HIV-positive children, higher IP-10 concentrations were observed in children with higher CD4 counts. Conclusions: IP-10 concentrations had good correlation with positive QTF/TST agreement, reinforcing its potential role for the diagnosis of LTBI. Interferon-γ and IP-10 responses in HIV-positive children need to be further investigated.

ELISPOT-IFN-γ assay instead of tuberculin skin test for detecting latent Mycobacterium tuberculosis infection in rheumatic patients candidate to anti-TNF-α treatment

In rheumatic patients candidate to anti-TNF-alpha treatment, there is an increased risk of developing tuberculosis (TB). The tuberculin skin test (TST), the standard diagnostic test for latent tuberculosis infection (LTBI), suffers low specificity and sensitivity. Here, we compared the performance characteristics of an in-house ELISPOT-IFN-gamma assay (using a restricted pool of Mycobacterium tuberculosis-specific peptides or MTP) to TST for the diagnosis of LTBI in 69 rheumatic patients candidate to anti-TNF-alpha treatment and in 60 healthy LTBI individuals. Among the 69 patients enrolled, 17 (25%) had a positive TST response and 15 (22%) a positive ELISPOT-MTP response. Among the patients with a positive TST result, eight had a positive and nine a negative ELISPOT-MTP response, whereas among the 49 patients with a negative TST result, 42 were ELISPOT-MTP negative, but seven (14%) were ELISPOT-MTP positive, with three indeterminate results. The agreement between the two tests was poor (k = 0.341, 95% CI = 0.060 to 0.622) and the test of symmetry was not significant (P = 0.8). Considering the ELISPOT assay, rheumatic patients had a reduced number of spot-forming cells after stimulation of lymphocytes with PHA or PPD when compared with healthy LTBI individuals. Thus, the ELISPOT-IFN-gamma assay performs better than the TST in recognizing patients with LTBI, on one hand reducing the number of patients submitted to isoniazid prophylaxis, and on the other hand, since the assay is less biased by immunosuppressive regimens than TST, recognizing LTBI patients among those with a negative TST response.

Evaluation of the Prognostic Value of IFN-γ Release Assay and Tuberculin Skin Test in Household Contacts of Infectious Tuberculosis Cases in Senegal

BackgroundChemoprophylaxis of contacts of infectious tuberculosis (TB) cases is recommended for TB control, particularly in endemic countries, but is hampered by the difficulty to diagnose latent TB infection (LTBI), classically assessed through response to the Tuberculin Skin Test (TST). Interferon-gamma release assays (IGRA) are proposed new tools to diagnose LTBI, but there are limited data on their ability to predict the development of active TB disease. To address this, we investigated the response to TST and IGRA in household contacts of infectious TB cases in a TB high-burden country and the potential correlation with development of TB.Methodology/Principal FindingsProspective household contacts study conducted in two health centres in Dakar, Senegal. A total of 2679 household contacts of 206 newly detected smear and/or culture positive index TB cases aged 18 years or greater were identified A TST was performed in each contact and an ESAT6/CFP10 ELISPOT assay performed in a random sample of those. Contacts were followed-up for 24 months. TB was diagnosed in 52 contacts, an incidence rate of 9.27/1000 person-years. In univariable analysis, the presence of positive TST (≥10 mm) and ELISPOT (>32 SFC/million PBMC) responses at baseline were associated with active TB during follow-up: Rate Ratio [RR] = 2.32 (95%CI:1.12–4.84) and RR = 2.09 (95%CI:0.83–5.31), respectively. After adjustment for age, sex and proximity to index case, adjusted RRs were 1.51 (95%CI:0.71–3.19) and 1.98 (95%CI:0.77–5.09), respectively. Restricting analysis to the 40 microbiologically confirmed cases, the adjusted RR for positive ELISPOT was 3.61 (95%CI:1.03–12.65). The median ELISPOT response in contacts who developed TB was 5-fold greater than in those who did not develop TB (p = 0.02).Conclusions/SignificanceTST and IGRAs are markers of a contact of the immune system with tubercle bacilli. In a TB endemic area, a high ELISPOT response may reflect increased bacterial replication that may subsequently be associated with development of TB disease and may have a prognostic value. Further longitudinal data are needed to assess whether IGRAs are reliable markers to be used for targeting chemoprophylaxis.

Tuberculin Skin Test and In Vitro Assays Provide Complementary Measures of Antimycobacterial Immunity in Children and Adolescents

Although many studies have compared in vitro TB diagnostic tests with the venerable tuberculin skin test (TST), there is little understanding of the quantitative relationship between critical measures of antimycobacterial immunity used to detect TB infection. We, therefore, decided to determine the degree of redundancy between quantitative read-outs of in vivo and in vitro assays of antimycobacterial immunity. We enrolled 475 healthy HIV-negative children and young adults living in a hyperendemic area of TB. We measured in vivo TST responses, and a 1:10 diluted 3- or 7-day whole-blood assay was used to determine the in vitro antigen-specific interferon (IFN)-gamma cytokine release. The frequency of antigen-specific IFN-gamma(+)CD4(+) and IFN-gamma(+)CD8(+) cells was tested using intracellular cytokine staining after 1 day incubation. In vivo TST responses segregated into two well-separated groups with either no measurable response (TST induration < 5 mm; n = 164) or a normally distributed group with TST indurations > or = 5 mm with peak at 15 mm (n = 260). In vitro assays provided a less pronounced separation of responders and nonresponders. Correlation analysis of responses among persons with TST > or = 5 mm demonstrated that extent of TST response was poorly correlated with IFN-gamma release (coefficients of correlation rho = 0.17-0.22) and frequency of IFN-gamma(+)CD4(+)/CD8(+) cells (rho = 0.05-0.17) across three stimulating antigens (Mycobacterium bovis bacillus Calmette-Guérin, purified protein derivative, early-secreted antigenic target-6). We conclude that in vivo and in vitro assays are nonredundant, complementary measures of antimycobacterial immunity. Both TST and in vitro assays provided valuable information about antimycobacterial immunity and by inference latent TB in the studied high-incidence TB settings.

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.