Tuberculin skin test versus interferon-gamma release assays for the diagnosis of tuberculosis infection

Bacillus Calmette-Guérin (BCG) Vaccine in America and Overseas: A Narrative Review

This narrative review examines the role of the Bacillus Calmette-Guérin (BCG) vaccine in global tuberculosis (TB) control efforts, with particular emphasis on the differences in vaccination policies between countries, such as the US, where routine BCG administration is not practiced. A significant complication of the BCG vaccine is false positive results in the tuberculin skin test (TST), often leading to misdiagnoses and unnecessary treatments. To address these issues, interferon-gamma release assays (IGRAs) have emerged as a more specific diagnostic tool that reduces false positives associated with prior BCG vaccination. However, despite advancements, public health challenges persist in accurately detecting latent and active TB, particularly in populations previously vaccinated with BCG. This review synthesizes existing literature to assess these challenges, emphasizing the need for updated policies and improved diagnostic tools for BCG-vaccinated populations in the US and globally. Recommendations include integrating IGRAs into routine practice and tailoring TB control strategies to mitigate the diagnostic complications of BCG.

Determination of the predictive factors for diagnostic positivity of nucleic acid amplification tests for diagnosing pulmonary tuberculosis

BACKGROUND

Tuberculosis (TB) remains a major threat to human health, and TB diagnostic methods remain unsatisfactory. Nucleic acid amplification tests (NAATs) show higher sensitivity compared with culture for the diagnosis of pulmonary TB (PTB). However, NAATs are expensive and cannot be easily implemented outside major medical centers. To improve the sensitivity of NAATs for PTB diagnosis, we investigated the predictive factors that might optimize NAAT utilization.

METHODS

A total of 1263 patients with suspected PTB were enrolled for evaluation. The sensitivity, specificity, and accuracy of methods including smear-microbiology, culture of Mtb and NAAT for Mycobacterium tuberculosis (Mtb) detection in sputum and bronchoalveolar lavage fluid samples were compared. Odds ratios and 95% confidence intervals were used to assess variables that might be associated with positive NAAT results for sputum and bronchoalveolar lavage fluid from patients with suspected PTB.

RESULTS

NAAT showed higher sensitivity for Mtb detection (61.1%) when compared with smear (9.0%) and Mtb culture (47.8%). We found that an elevated erythrocyte sedimentation rate, the presence of cavities, and positive interferon-γ release assay (IGRA) results were indicative of positive Mtb detection by NAAT. Moreover, individuals who had all three of these characteristics showed an 86% diagnostic positivity for PTB from Mtb detection by NAAT.

CONCLUSIONS

Our study suggests that an elevated erythrocyte sedimentation rate, a positive IGRA result, and the presence of pulmonary cavities are helpful factors for predicting positive Mtb detection by NAAT. Patients with the three positive clinical markers should undergo NAAT for Mtb detection because they are the most likely individuals to be bacteriologically confirmed as having TB.

Clinical features and long-term treatment outcomes in choroidal tuberculoma

PURPOSE

To investigate the clinical features and treatment outcomes of patients with choroidal tuberculoma.

METHODS

In this retrospective, observational case series, the medical records of five patients with choroidal tuberculoma who were followed up at a university hospital for at least 6 months were analyzed.

RESULTS

Of five patients, one was male and four were female. The overall mean age was 38.0 ± 9.4 years (mean follow-up: 41.2 ± 33.8 months). Tuberculin skin test was performed in three patients, and it was positive in two of them. Interferon-gamma assay was performed in two patients and was positive in all two. Three patients had systemic tuberculosis involving the lung or other organs. Five patients were treated with antitubercular therapy for a period of 9.6 ± 8.6 months. Systemic corticosteroid treatment was performed in 3 patients, with a period of 3.5 ± 0.7 months. One patient with a recurrent vascularized tuberculoma was successfully treated with single intravitreal bevacizumab injection.

CONCLUSION

Choroidal tuberculoma can develop without evidence of systemic tuberculosis and can recur despite antitubercular treatment. High index of suspicion is important in early detection, and management of choroidal tuberculoma. In cases of suspected choroidal tuberculoma, positive results on immunological tests would be sufficient to initiate antitubercular therapy even if radiological evidence of systemic tuberculosis is not found. Antitubercular therapy combined with systemic corticosteroids provided favorable results. Intravitreal injection of anti-vascular endothelial growth factor may be considered for highly vascularized choroidal tuberculoma.

A Pilot TB Screening Model in a U.S. Prison Population Using Tuberculin Skin Test and Interferon Gamma Release Assay Based on Country of Origin

The objective of this study was to compare tuberculosis (TB) screening results before and after implementation of a stratified testing strategy screening pilot study, incorporating interferon gamma release assay (IGRA) and tuberculin skin test (TST), based on country of origin. In 2015, the Washington State Department of Corrections began screening people born outside of the United States for TB with IGRA, while U.S.-born people continued screening by TST. Of 405 (75%) foreign-born men screened with IGRA, 403 had valid test results and IGRA screening positivity was 10.4% (N = 42). In contrast, among 5,940 primarily U.S-born men screened with TST, 24 (0.4%) were positive. Overall positivity was 1.05%, similar to TST-only positivity in 2013 (1.05%) and 2014 (0.85%). Incorporating IGRA screening among foreign-born persons was feasible in this state prison system.

Characterization of and advanced diagnostic methods for ocular tuberculosis and tuberculosis

Tuberculosis (TB) is an airborne infection caused by Mycobacterium tuberculosis that usually affects the lungs. Timely treatment of active TB, diagnosis and prevention of latent TB are very important. However, extrapulmonary TB affects almost any tissues around the eye and orbit, and it then requires a high degree of suspicion to accurately diagnose. Diagnostic delays are common and may lead to morbidity. For ophthalmologists and infectious disease specialists, it is important to work together to accurately diagnose and treat ocular tuberculosis (OTB) to prevent vision loss. This review reports the latest advanced diagnostic methods for active TB and latent TB as well as various known manifestations of OTB. Important elements of diagnosis and treatment are also reviewed.

Latent tuberculosis infection in transplant candidates: a systematic review and meta-analysis on TST and IGRA

INTRODUCTION

The diagnostic accuracy of interferon-gamma release assays (IGRAs) and the tuberculin skin test (TST) for latent tuberculosis infection (LTBI) in transplant candidates is uncertain.

METHODS

Pubmed, Embase and Cochrane library were searched to identify relevant studies. Quality of included studies was assessed with RevMan5 software (via GUADAS2 checklist). Accuracy measures of IGRAs and TST assays (sensitivity, specificity and others) were pooled with random effects model. Data were analyzed by STATA and Meta-DiSc.

RESULTS

Twenty-eight studies were selected for full review, and 16 were included in the final analysis. The pooled sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (PLR), negative likelihood ratio (NLR) and diagnostic odds ratio (DOR) for TST were 46% [95% confidence interval (CI) 38-54%], 86% (95% CI 75-93%), 46.3% (95% CI 40-52), 88.7% (95% CI 87-89), 3.3 (95% CI 1.6-6.4), 0.63 (95% CI 0.52-0.77) and 5 (95% CI 2-12), respectively. For QFT-G, the pooled sensitivity, specificity, PPV, NPV, PLR, NLR, and DOR were 58% (95% CI 41-73%), 89% (95% CI 77-95%), 72.7% (95% CI 68-76), 80.6% (95% CI 78-82), 5.3 (95% CI 2.0-14.0), 0.47 (95% CI 0.30-0.75) and 11 (95% CI 3-46), respectively. Likewise, for T-SPOT.TB, the pooled sensitivity, specificity, PPV, NPV, PLR, NLR, and DOR were 55% (95% CI 40-70%), 92% (95% CI 87-95%), 60.4% (95% CI 47-72), 90.2% (95% CI 86-92), 6.7 (95% CI 4.0-11.1), 0.52 (95% CI 0.31-0.85) and 16 (95% CI 7-37), respectively.

CONCLUSIONS

IGRAs were more sensitive and specific than the TST with regard to the diagnosis of LTBI in the transplant candidates. They have added value and can be complementary to TST.

Active Tuberculosis Is Characterized by Highly Differentiated Effector Memory Th1 Cells

Despite advances in diagnosing latent Mycobacterium tuberculosis infection (LTBI), we still lack a diagnostic test that differentiates LTBI from active tuberculosis (TB) or predicts the risk of progression to active disease. One reason for the absence of such a test may be the failure of current assays to capture the dynamic complexities of the immune responses associated with various stages of TB, since these assays measure only a single parameter (release of IFN-γ) and rely on prolonged (overnight) T cell stimulation. We describe a novel, semi-automated RNA flow cytometry assay to determine whether immunological differences can be identified between LTBI and active TB. We analyzed antigen-induced expression of Th1 cytokine mRNA after short (2- and 6-h) stimulation with antigen, in the context of memory T cell immunophenotyping. IFNG and TNFA mRNA induction was detectable in CD4+ T cells after only 2 h of ex vivo stimulation. Moreover, IFNG- and TNFA-expressing CD4+ T cells (Th1 cells) were more frequent in active TB than in LTBI, a difference that is undetectable with conventional, protein-based cytokine assays. We also found that active TB was associated with higher ratios of effector memory to central memory Th1 cells than LTBI. This effector memory phenotype of active TB was associated with increased T cell differentiation, as defined by loss of the CD27 marker, but not with T cell exhaustion, as determined by PD-1 abundance. These results indicate that single-cell-based, mRNA measurements may help identify time-dependent, quantitative differences in T cell functional status between latent infection and active tuberculosis.

Indicators for prediction of Mycobacterium tuberculosis positivity detected with bronchoalveolar lavage fluid

BACKGROUND

The diagnosis of active pulmonary tuberculosis (TB) remains a challenge in clinic, especially for sputum negative pulmonary TB. Bronchoalveolar lavage fluid (BALF) has higher sensitivity than sputum for detection of Mycobacterium tuberculosis (Mtb). However, bronchoscopy is invasive and costly, and not suitable for all patients. In order to make TB patients get more benefit from BALF for diagnosis, we explore which indicator might be used to optimize the choice of bronchoscopy.

METHODS

A total of 1539 sputum-smear-negative pulmonary TB suspects who underwent bronchoscopy were recruited for evaluation. The sensitivity, specificity and accuracy of Mtb detection in sputum and BALF were compared. Odds ratios and 95% confidence intervals were used to assess variables that associated with positive acid-fast bacilli (AFB) smear, Mtb culture and nucleic acid amplification test (NAAT) of BALF in sputum-negative and non-sputum-producing pulmonary TB suspects.

RESULTS

BALF has significantly higher sensitivity (63.4%) than sputum (43.5%) for Mtb detection by culture and NAAT. 19.7% (122/620) sputum-negative and 40.0% (163/408) non-sputum-producing suspects had positive bacteriological results in BALF. Among sputum-negative and non-sputum-producing pulmonary TB suspects, the positivity of Mtb detection in BALF is associated with a younger age, the presence of pulmonary cavities and a positive result of interferon-gamma release assay (IGRA). Sputum-negative patients under 35 years old with positive IGRA and pulmonary cavity had 84.8% positivity of Mtb in BALF.

CONCLUSIONS

Our study indicated that combination of age, the presence of pulmonary cavity, and the result of IGRA is useful to predict the positivity of Mtb detection in BALF among sputum-negative and non-sputum producing pulmonary TB suspects. Those who are under 35 years old, positive for the presence of pulmonary cavity and IGRA, should undergo bronchoscopy to collect BAFL for Mtb tests, as they have the highest possibility to get bacteriologically confirmation of TB.

Identification of mycobacterial bacterioferritin B for immune screening of tuberculosis and latent tuberculosis infection

OBJECTIVES

It remains necessary and urgent to search for novel mycobacterial antigens to increase the sensitivity and specificity for tuberculosis (TB) diagnosis and latent TB infection (LTBI) screening. Antigens capable of inducing strong immune responses during Mycobacterium tuberculosis (M.tb) infection would be good candidates.

METHODS

Cellular responses specific to M.tb derived bacterioferritin B (BfrB) were assessed by IFN-γ ELISPOT in three human cohorts, including healthy controls (HCs), LTBI population and pulmonary TB (PTB) patients. Its significance in TB diagnosis and LTBI identification was further analyzed.

RESULTS

BfrB-specific IFN-γ responses in PTB and LTBI groups were significantly higher than that in HCs. However, BfrB-specific IFN-γ release was not as strong as that to ESAT-6 or CFP-10 in PTB patients whereas comparable in LTBI cohort with possible complementary properties to ESAT-6 or CFP-10. More interestingly, there were a considerable number of HCs with high BfrB-specific cellular responses. When HCs with high BfrB-specific cellular responses were subgrouped into ESAT-6/CFP-10^hi (SFUs = 3, 4, 5) and ESAT-6/CFP-10^lo (SFUs < 3) groups, those who belonged to ESAT-6/CFP-10^hi group exhibited higher PPD responsiveness than ESAT-6/CFP-10^lo group.

CONCLUSIONS

PTB and LTBI groups exhibit higher BfrB-specific IFN-γ responses than HCs. Although BfrB is not as immunodominant as ESAT-6/CFP-10 during acute M.tb infection, comparable BfrB-specific cellular immune responses are observed in LTBI population with the potential to increase the sensitivity for LTBI screening. Moreover, strong BfrB-specific IFN-γ release in the healthy cohort is probably cautionary in identifying leaky LTBI from HCs. BfrB might thus be considered as an additional biomarker antigen for LTBI identification.

Use of interferon-gamma release assay and tuberculin skin test in diagnosing tuberculosis in Lithuanian adults: A comparative analysis

BACKGROUND AND OBJECTIVE

Lithuania belongs to the group of countries with a high-incidence of tuberculosis (TB). Some scientific studies show that the interferon-gamma release assay is more accurate and correlates more highly with TB exposure as compared to the tuberculin skin test (TST). This study aimed at comparing the efficacy between the T SPOT TB and TST for diagnosing TB among Lithuanian adults.

MATERIALS AND METHODS

Individuals with diagnosed TB, healthcare workers with known risk for TB and individuals without any known risk for TB underwent clinical examinations, interviews about their history of TB exposure and chest radiography. Then the TST and the T SPOT TB were performed on patients.

RESULTS

A positive T SPOT TB was more common in the group with diagnosed TB compared to healthcare workers and the low risk for TB groups (97.5%, 36.4%, and 0%, respectively, P<0.01). Positive TST results did not differ between the groups with diagnosed TB and the healthcare workers (92.5% vs. 95.5%, P>0.05). Agreement between TST and T SPOT TB was poor (kappa 0.14, P>0.05). T SPOT TB had higher specificity and sensitivity compared to TST (area under the ROC 0.9±0.04, P<0.01, vs. 0.5±0.06, P>0.05).

CONCLUSIONS

The T SPOT TB showed greater accuracy in diagnosing TB than TST did. Positive T SPOT TB result but not the TST was more common in patients with diagnosed TB.

Role of Interferons in the Development of Diagnostics, Vaccines, and Therapy for Tuberculosis

Tuberculosis (TB) is an airborne infection caused by Mycobacterium tuberculosis (Mtb). About one-third of the world's population is latently infected with TB and 5–15% of them will develop active TB in their lifetime. It is estimated that each case of active TB may cause 10–20 new infections. Host immune response to Mtb is influenced by interferon- (IFN-) signaling pathways, particularly by type I and type II interferons (IFNs). The latter that consists of IFN-γ has been associated with the promotion of Th1 immune response which is associated with protection against TB. Although this aspect remains controversial at present due to the lack of established correlates of protection, currently, there are different prophylactic, diagnostic, and immunotherapeutic approaches in which IFNs play an important role. This review summarizes the main aspects related with the biology of IFNs, mainly associated with TB, as well as presents the main applications of these cytokines related to prophylaxis, diagnosis, and immunotherapy of TB.

Performance of interferon-γ release assays in the diagnosis of confirmed active tuberculosis in immunocompetent children: a new systematic review and meta-analysis

Background

Tuberculosis (TB) is a global public health problem, causing morbidity and mortality in adults and children. The most reliable diagnostic tools currently available are the in vivo Tuberculin Skin Test (TST) and the ex vivo Interferon-γ release assays (IGRAs). Several clinical, radiological, and bacteriological features make the detection of active (overt disease) TB in children difficult. Although recently developed immunological assays such as QuantiFERON-TB Gold In-Tube (QFT-IT) and T-SPOT®.TB are commonly used to identify active TB in adults, different evidence is required for diagnosis in children. The purpose of this study was to reassess the sensitivity and specificity of IGRAs in detecting microbiologically confirmed active TB in immunocompetent children.

Methods

A systematic review and meta-analysis of studies reporting on the diagnostic accuracy of tests for TB in immunocompetent children aged 0–18 years, with confirmation by positive M. tuberculosis cultures, were undertaken. Electronic databases were searched up to September 2015 and study quality assessment was performed using QUADAS-2.

Results

Fifteen studies were included in our meta-analysis. Results showed that there were no significant differences in sensitivity between TST (88.2 %, 95 % confidence interval [CI] 79.4–94.2 %), QFT-IT (89.6 %, 95 % CI 79.7–95.7 %) and T SPOT (88.5 %, 95 % CI 80.4–94.1 %). However, both QFT-IT (95.4 %, 95 % CI 93.8–96.6 %) and T-SPOT (96.8 %, 95 % CI 94.2–98.5 %) have significantly higher specificity than TST (86.3 %, 95 % CI 83.9–88.6 %).

Conclusions

QFT-IT and T-SPOT have higher specificity than TST for detecting active TB cases in immunocompetent children.

High Discordance Between Pre-US and Post-US Entry Tuberculosis Test Results Among Immigrant Children: Is it Time to Adopt Interferon Gamma Release Assay for Preentry Tuberculosis Screening?

BACKGROUND

Since 2007, immigration applicants 2-14 years old with a tuberculin skin test (TST) ≥10 mm and an otherwise negative evaluation for tuberculosis (TB) are assigned a classification for TB infection and instructed to seek domestic evaluation upon arrival in the US in accordance with Centers for Disease Control and Prevention instructions. We examined the characteristics and outcome of domestic evaluation of immigrant children who arrived in California with a positive TST on preimmigration examination to inform the preimmigration TB screening process.

METHODS

Retrospective analysis of the characteristics and results of domestic evaluation of immigrants 2-14 years old who arrived in California with a classification for TB infection during October 1, 2008-September 30, 2013 was performed. TB disease was determined by matching preimmigration records with the California TB registry.

RESULTS

Among a total of 12,544 immigrant children included, 7786 (62%) were evaluated for TB postentry. Of these, 5243 (67%) were tested with TST or interferon gamma release assay (IGRA), and 2371 (45%) had a positive test. Of those tested with IGRA (n = 4035), 914 (23%) were positive. The proportion with positive IGRA increased significantly with age (years): 2-4 (11%), 5-9 (19%), 10-14 (28%), P < 0.0001; was lowest among arrivers from China (6%) and highest among arrivers from Mexico (48%). Nine children (0.07%) had TB disease within 5 years after arrival.

CONCLUSIONS

The majority of immigrant children with a positive preimmigration TST tested negative for TB infection on domestic evaluation using TST or IGRA. Inclusion of IGRA in preimmigration TB screening is likely to reduce subsequent testing, treatment and cost of evaluations among immigrant children to the US.

Combined use of Mycobacterium tuberculosis-specific CD4 and CD8 T-cell responses is a powerful diagnostic tool of active tuberculosis

Immune-based assays are promising tools to help to formulate diagnosis of active tuberculosis. A multiparameter flow cytometry assay assessing T-cell responses specific to Mycobacterium tuberculosis and the combination of both CD4 and CD8 T-cell responses accurately discriminated between active tuberculosis and latent infection.