Highly discordant T cell responses in individuals with recent exposure to household tuberculosis

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.

[Study of contacts in children and adolescents using the QuantiFERON®-TB Gold In-Tube]

OBJECTIVE

To compare the results of the Mantoux Tuberculin Test (TT) and the QuantiFERON TB® Gold In-Tube (QFT-GIT) in a population of children and adolescents with TB contacts.

MATERIAL AND METHODS

A prospective study using data collected on children and adolescents (< 17years) from a Health District of 300,000 inhabitants in the Basque Country (Spain) recruited into a TB contact study over a period of almost three years. The study included performing the Tuberculin Test using the Mantoux technique (with 2-TU of RT-23 PPD RT23 and Tween 80), and the QFT-GIT simultaneously, and collecting the demographic and clinical data.

RESULTS

Of the 160 children included in the study, 14% had a positive TT (≥ 5mm) and 11% a positive QFT-GIT. There was 95%-96% agreement between the tests, depending on the TT cut-off point chosen, and was higher in non-vaccinated children (100%) and in children less than 5 years-old (100%). A significant relationship was observed between a positive result for both tests with exposure in the home. The use of QFT-GIT in the screening of latent TB infection could reduce preventive treatments by 28%-34% compared with conventional screening with the TT.

CONCLUSIONS

The behaviour of QFT-GIT was comparable to the TT in identifying children with a tuberculosis infection; therefore it could potentially replace the TT.

Discriminating between latent and active tuberculosis with multiple biomarker responses

We sought to identify biomarker responses to tuberculosis specific antigens which could 1) improve the diagnosis of tuberculosis infection and 2) allow the differentiation of active and latent infections. Seventy subjects with active tuberculosis (N = 12), latent tuberculosis (N = 32), or no evidence of tuberculosis infection (N = 26) were evaluated. We used the Luminex Multiplexed Bead Array platform to simultaneously evaluate 25 biomarkers in the supernatant of whole blood samples following overnight stimulation using the Quantiferon(®) Gold In-Tube kit. We defined the response to stimulation as the difference (within an individual patient) between the response to the pooled tuberculosis antigens and the negative control. IP-10 response was significantly higher in tuberculosis-infected (active or latent) subjects compared to the uninfected group (p < 0.0001). Among the 25 parameters, expression levels of IL-15 and MCP-1 were found to be significantly higher in the active tuberculosis group compared to the latent tuberculosis group (p = 0.0006 and 0.0030, respectively). When combined, IL-15 and MCP-1 accurately identified 83% of active and 88% of latent infections. The combination of IL-15 and MCP-1 responses was accurate in distinguishing persons with active tuberculosis from persons with latent tuberculosis in this study.

Tuberculin skin test and interferon-γ release assay show better correlation after the tuberculin 'window period' in tuberculosis contacts

BACKGROUND

T-cell interferon-gamma release assays (IGRAs) have been shown to be effective tools for the detection of Mycobacterium tuberculosis infection, offering an enhanced specificity compared to the tuberculin skin test (TST). Most tuberculosis (TB) contact studies have shown a better correlation of IGRA with the intensity of M. tuberculosis exposure than that obtained using the TST. However, the correlation between tests performed before and after the tuberculin 'window period' (time between infection and when the immunological response becomes measurable) remains to be studied.

METHODS

A longitudinal prospective analysis was performed in TB contacts. We analyzed the correlation between a commercially available IGRA (QuantiFERON®-TB Gold in-Tube, QFT) and the TST before and after the tuberculin window period (2 months). Concordance between both tests was assessed using the Kappa coefficient (κ). Correlation of both tests with the degree of TB exposure was also analyzed.

RESULTS

One hundred and fifty-two TB contacts were included in the study. Agreement between the TST and IGRA was better after the window period (κ = 0.60 at the first visit and κ = 0.73 after 2 months), especially for non-BCG vaccinated subjects (κ = 0.81). Both a positive TST and QFT were correlated, after the window period, with the size of place of contact (the smaller the place of contact, the higher the probability of having a positive test) (p = 0.022 and p = 0.02, respectively) and with the total numbers of hours spent with the index case (p = 0.006 for TST and p = 0.007 for QFT).

CONCLUSIONS

IGRAs are a good alternative to the TST in contact tracing studies, especially after the tuberculin window period.

Diagnosis of pulmonary tuberculosis in children: new advances

The global burden of childhood pulmonary TB has been underappreciated, in part due to difficulties in obtaining microbiological confirmation of disease. Most HIV-uninfected children can be diagnosed using a combination of clinical and epidemiological features, tuberculin skin testing and chest radiography, as represented in different scoring systems. However, accurate microbiologic diagnosis has become increasingly important for timely use of effective treatment. Mycobacterial culture confirms the diagnosis of TB and provides drug susceptibility data but is not available in most areas with a high TB prevalence. Moreover, culture has poor sensitivity in children who usually have paucibacillary disease. The HIV epidemic has made definitive diagnosis even more challenging due to nonspecific clinical and radiological signs. In high HIV-prevalence areas, scoring systems have been especially variable, lacking sensitivity and specificity. Newer methods for diagnosis are aimed either at detecting the organism or a specific host immune response. Methods for organism detection have focused on collection of better samples, improved culture techniques, molecular methods or antigen detection. Recent advances include the use of sputum induction for obtaining a more reliable specimen, faster and more sensitive culture methods, and rapid detection of the organism and drug resistance based on nucleic acid amplification. Improved methods for detecting a specific host response have largely focused on the use of IFN-g release assays. Even with newer methods, accurately diagnosing childhood TB may be challenging. Greater efforts to obtain a microbiologic diagnosis should be made in children, even in primary care settings. Further research to develop a more accurate, cost-effective and simple diagnostic test for childhood TB is urgently needed.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

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.

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.