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

Varying clinical presentations of nontuberculous mycobacterial disease : Similar to but different from tuberculosis

The incidence rate of pulmonary nontuberculous mycobacterial disease (PNTMD) in Japan is the highest among major industrialized nations. Although the typical clinical course and radiological manifestations of PNTMD are different from those of pulmonary tuberculosis (TB), confusion about these mycobacterial diseases leads to a diagnostic pitfall. Diagnostic challenges include the coexistence of Mycobacterium tuberculosis (MTB) and nontuberculous mycobacteria (NTM), false positives for NTM in MTB nucleic acid amplification tests, microbial substitution, and abnormal radiological manifestations caused by NTM. Features of extrapulmonary NTM diseases, such as pleurisy, vertebral osteomyelitis, and disseminated disease, are different from the corresponding tuberculous diseases. Moreover, the immunological background of the patient (status of human immunodeficiency virus infection with or without antiviral therapy, continuation or discontinuation of immunosuppressive therapy, use of immune checkpoint inhibitor, pregnancy and delivery, etc.) influences the pathophysiology of mycobacterial diseases. This review describes the varying clinical presentations of NTM disease with emphasis on the differences from TB. J. Med. Invest. 68 : 220-227, August, 2021.

The Association between QuantiFERON-TB Gold Test and Clinical Manifestations of Uveitis in the United States

PURPOSE

To report the prevalence of QuantiFERON-TB Gold (QFT-G) positivity among uveitis patients compared to general population and to evaluate the differences in clinical features of uveitis.

DESIGN

Retrospective cohort study.

METHODS

SETTING: Institutional.

PATIENT POPULATION

418 consecutive new uveitis patients, regardless of clinical suspicion, were tested for QFT-G.

OBSERVATION PROCEDURES

Demographics, TB risk factors, clinical characteristics of uveitis were collected.

MAIN OUTCOME MEASURES

The frequency of QFT-G positivity among uveitis patients and characteristic clinical features among QFT-G positive patients.

RESULTS

QFT-G positivity was found in 60/418 patients with uveitis (14.4%, 95% CI: 11.18 - 18.14) higher than the general US population (5%, 95% CI: 4.2 - 5.8, p<.001). Age, gender and residence were similar between QFT-G positive and negative groups. Uveitis patients with positive QFT-G were more likely to be foreign born or have a recent travel history (OR:5.84; 95% CI: 2.83 - 12.05; p<.001). QFT-G positive patients were more likely to present with granulomatous uveitis (OR 2.90; 95%CI 1.36 - 6.21; p=.006). No significant association was found with specific clinical features such as choroiditis, retinal vasculitis, occlusive vasculitis, and serpiginoid choroiditis (p>.05 for each). Prevalence of TB-uveitis based on treatment response was 1.19%.

CONCLUSIONS

Our study demonstrates significantly higher prevalence of QFT-G positivity among uveitis patients compared to average US population. Characteristic signs of TB uveitis reported in endemic countries were not seen in this cohort. Implications of higher prevalence of QFT-G positivity among uveitis patients require further investigation.

Safety Evaluation of Recombinant Fusion Protein RP22 as a Skin Test Reagent for Tuberculosis Diagnosis: A Phase I Clinical Trial

INTRODUCTION

This phase I clinical trial was conducted to evaluate the safety of RP22 as a skin test reagent for tuberculosis (TB) diagnosis and to explore the appropriate dosage.

METHODS

We used a randomized, double-blind, placebo-controlled identification allergen (IA) skin test. A total of 72 healthy adult volunteers with negative chest X-ray results were randomized into six groups and given a QuantiFERON-TB Gold (QFT) test. Of the 12 participants in each group, eight received RP22 and four received placebo. The doses of RP22 in the six experimental groups ranged from 0.1 to 4.0 μg in a single intradermal injection of 0.1 ml. Skin reactions and adverse events were recorded at intervals.

RESULTS

All doses of RP22 except the highest were well tolerated and safe. No serious adverse events associated with the injection were observed in all groups. There were 11 participants who had positive QFT results, eight had a skin reaction with a redness or induration area diameter of greater than 10 mm at 48-72 h, one had no skin reaction. Among the 60 negative-QFT participants, none had a reaction area diameter of greater than 10 mm.

CONCLUSION

The RP22 skin test was well tolerated and safe, it could play a key role in screening for latent tuberculosis infection (LTBI) by providing a much-wanted alternative to the tuberculin skin test (TST) and interferon-γ release assays (IGRAs).

Leucine-rich alpha 2 glycoprotein is a new marker for active disease of tuberculosis

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) is a global health problem. At present, prior exposure to Mtb can be determined by blood-based interferon-gamma release assay (IGRA), but active TB is not always detectable by blood tests such as CRP and ESR. This study was undertaken to investigate whether leucine-rich alpha-2 glycoprotein (LRG), a new inflammatory biomarker, could be used to assess active disease of TB. Cynomolgus macaques pretreated with or without Bacille Calmette-Guerin (BCG) vaccination were inoculated with Mtb to induce active TB. Blood was collected over time from these animals and levels of LRG as well as CRP and ESR were quantified. In the macaques without BCG vaccination, Mtb inoculation caused extensive TB and significantly increased plasma CRP and LRG levels, but not ESR. In the macaques with BCG vaccination, whereas Mtb challenge caused pulmonary TB, only LRG levels were significantly elevated. By immunohistochemical analysis of the lung, LRG was visualized in epithelioid cells and giant cells of the granulation tissue. In humans, serum LRG levels in TB patients were significantly higher than those in healthy controls and declined one month after anti-tubercular therapy. These findings suggest that LRG is a promising biomarker when performed following IGRA for the detection of active TB.

A tuberculosis outbreak in a psychiatric hospital: Kanagawa, Japan, 2012

In January 2012, an inpatient in a ward of a psychiatric hospital with nearly 300 beds in Kanagawa, Japan, was diagnosed with sputum smear-positive pulmonary tuberculosis (TB). Here we characterise the TB outbreak cases and identify the population at risk. TB was diagnosed when a person tested bacteriologically positive for TB or was determined to have TB by a physician. A latent TB infection (LTBI) case was defined as a person tested positive by interferon-gamma release assay (IGRA). A total of 125 contacts were screened via IGRA and chest X-ray. In all, 15 TB and 15 LTBI cases were found by the end of October 2012, and thereafter no additional TB case was found. Of the 15 TB cases, eight were culture-positive and all the isolates had identical variable number tandem repeat patterns. Twenty-four of the 56 (42.9%, 95% confidence interval (CI) 29.7-56.8) inpatients in the ward had either TB or LTBI with a relative risk of 8.6 (95% CI 1.2-59.3), compared to the staff members who did not work full-time in the ward (one of 20 (5.0%, 95% CI 0.0-24.9)). We recommend that psychiatric hospitals conduct periodic screening of staff members and inpatients for TB to prevent nosocomial TB outbreaks.

Ten Cases of Intestinal Tuberculosis Which Were Initially Misdiagnosed as Inflammatory Bowel Disease

Objective Intestinal tuberculosis (ITB) and inflammatory bowel disease (IBD) frequently present with similar clinical, endoscopic and pathological features, therefore it is difficult to differentiate between them. The aim of this study was to elucidate the diagnostic delay and prognosis of ITB cases, initially misdiagnosed as IBD. Methods ITB cases were selected from the hospitalized patient list between April 2004 and March 2017 in a tuberculosis center in Japan. We retrospectively evaluated the initial diagnosis, clinical characteristics, endoscopic and pathological findings, bacterial examinations, treatment and prognosis. Results Among 66 ITB patients, ten patients were initially misdiagnosed as IBD. Seven patients were male and the median age was 60.5 years (23-74 years). After the diagnosis of IBD, all the patients were treated with mesalazine, in addition to corticosteroids in two patients and sequential azathioprine and infliximab in one. The median duration of diagnostic delay was 5.5 months (range 0.5-17 months). Eight patients had active pulmonary tuberculosis at the diagnosis of ITB. Acid-fast bacilli were confirmed in four of seven patients by reevaluation of the pathological specimens at the IBD diagnosis. Two patients needed intestinal resection and one with erroneous corticosteroid use for IBD died due to respiratory failure in spite of receiving appropriate treatment for tuberculosis. Conclusion ITB patients were frequently misdiagnosed and treated as IBD, thus resulting in a poor clinical outcome even after finally making a correct diagnosis and administering appropriate treatment. On diagnosis of IBD and/or treatment failure, chest radiograph and acid-fast bacilli of the pathological specimens should be carefully evaluated in order to rule out tuberculosis.

Depressed Gamma Interferon Responses and Treatment Outcomes in Tuberculosis Patients: a Prospective Cohort Study

Immunosuppression induced by Mycobacterium tuberculosis is important in the pathogenesis of active tuberculosis (TB). However, the impact of depressed TB-specific and non-TB-specific gamma interferon (IFN-γ) response on the treatment outcomes of TB patients remains uncertain. In this prospective cohort study, culture- or pathology-proven active TB patients were enrolled and QuantiFERON-TB Gold In-Tube (QFT-GIT) assays were performed before the initiation of anti-TB treatment. TB-specific IFN-γ responses (TB antigen tube subtracted from the nil tube) and non-TB-specific IFN-γ responses (mitogen tube subtracted from the nil tube) were measured and associated with treatment outcomes, including 2-month culture conversion and on-treatment mortality. A total of 212 active TB patients were included in the analysis. We observed a close correlation between decreased lymphocyte count and lower non-TB-specific IFN-γ responses but not TB-specific IFN-γ responses. Patients with lower non-TB-specific IFN-γ responses had lower 2-month culture conversion rate (71.1% versus 84.7%, respectively; P = 0.033) and higher on-treatment mortality (22.6% versus 5.7%, respectively; P = 0.001) than those with higher non-TB-specific IFN-γ responses. In multivariate analysis, depressed non-TB-specific IFN-γ response was an independent factor associated with 2-month sputum culture nonconversion (odds ratio [OR], 2.49; 95% CI [95% confidence interval], 1.05 to 5.90) and on-treatment mortality (hazard ratio [HR], 2.76; 95% CI, 1.15 to 6.62). In contrast, depressed TB-specific IFN-γ responses were significantly associated with higher on-treatment mortality in univariate analysis but not in multivariate analysis. Our findings suggest that depressed non-TB-specific responses, but not TB-specific IFN-γ responses, as measured by QFT-GIT before the initiation of anti-TB treatment, were significantly associated with worse treatment outcomes in TB patients.

A tuberculosis contact investigation involving a large number of contacts tested with interferon-gamma release assay at a nursing school: Kanagawa, Japan, 2012

In May 2012, a teacher of a nursing school with about 300 staff members and students in Japan was diagnosed with sputum smear-positive pulmonary tuberculosis (TB), leading to an investigation involving nearly 300 contacts. We describe the contacts' closeness to the index TB patient and the likelihood of TB infection and disease. A case of TB was defined as an individual with positive bacteriological tests or by a physician diagnosis of TB. A latent TB infection (LTBI) case was defined as an individual who had a positive interferon-gamma release assay (IGRA). A total of 283 persons screened with IGRA were analysed. Eight persons (2.8%, 95% confidence interval [CI]: 1.2-5.4) tested positive by IGRA; one student who had intermediate (less than 10 hours) contact with the index patient was found to have pulmonary TB by chest X-ray. The positivity in IGRA among staff members with very close contact with the index patient (4 of 21, 19%, 95% CI: 5.4-42%) with a statistically significant relative risk of 17 (95% CI: 2.0-140) was high compared with that of the intermediate contacts (1 of 88, 1.1% [95% CI: 0.028-6.2]). There was a statistically significant trend in the risk of TB infection and closeness with the index patient among the staff members and students (P < 0.00022). In congregate settings such as schools, the scope of contact investigation may have to be expanded to detect a TB case among those who had brief contact with the index patient.

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

Background

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

Methods

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

Results

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

Conclusion

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

Ocular Tuberculosis

Ocular tuberculosis is an extrapulmonary mycobacterial infection with variable manifestations. The reported incidence of ocular involvement varies considerably, depending on the criteria used for diagnosis and the population sampled. However, tuberculosis is thought to affect the lungs in 80% of patients, with the remaining 20% being affected in other organs, such as the eye. It is imperative for physicians to consider this diagnosis in their differential, as ocular tuberculosis can present in a fashion similar to that of more common conditions causing ocular inflammation. In addition, prompt recognition of the clinical signs and symptoms leads to quicker initiation of antituberculosis therapy.

Miliary Tuberculosis

Miliary tuberculosis (TB) results from a massive lymphohematogenous dissemination of Mycobacterium tuberculosis bacilli and is characterized by tiny tubercles evident on gross pathology resembling millet seeds in size and appearance. The global HIV/AIDS pandemic and widespread use of immunosuppressive drugs and biologicals have altered the epidemiology of miliary TB. Considered to be predominantly a disease of infants and children in the pre-antibiotic era, miliary TB is increasingly being encountered in adults as well. The clinical manifestations of miliary TB are protean and nonspecific. Atypical clinical presentation often delays the diagnosis. Clinicians, therefore, should have a low threshold for suspecting miliary TB. Focused, systematic physical examination helps in identifying the organ system(s) involved, particularly early in TB meningitis, as this has therapeutic significance. Fundus examination for detecting choroid tubercles offers a valuable clinical clue for early diagnosis, as their presence is pathognomonic of miliary TB. Imaging modalities help in recognizing the miliary pattern, defining the extent of organ system involvement. Examination of sputum, body fluids, image-guided fine-needle aspiration cytology or biopsy from various organ sites, needle biopsy of the liver, bone marrow aspiration, and biopsy should be done to confirm the diagnosis. Cytopathological, histopathological, and molecular testing (e.g., Xpert MTB/RIF and line probe assay), mycobacterial culture, and drug susceptibility testing must be carried out as appropriate and feasible. Miliary TB is uniformly fatal if untreated; therefore, early initiation of specific anti-TB treatment can be lifesaving. Monitoring for complications, such as acute kidney injury, air leak syndromes, acute respiratory distress syndrome, adverse drug reactions such as drug-induced liver injury, and drug-drug interactions (especially in patients coinfected with HIV/AIDS), is warranted.

Interferon-gamma release assays in patients with Mycobacterium kansasii pulmonary infection: A retrospective survey

OBJECTIVES

Interferon-gamma release assays (IGRAs) can be positive in patients infected with Mycobacterium kansasii (M. kansasii), which carries some of Mycobacterium tuberculosis specific antigens adopted for IGRAs. Our aim is to evaluate positive rate and factors associated with positive IGRAs in patients with M. kansasii pulmonary infection.

METHODS

We retrospectively investigated 105 M. kansasii cases in which IGRAs were performed before or ≦14 days after treatment initiation. Clinical characteristics including a history of tuberculosis, radiographic features and laboratory data were collected from medical records.

RESULTS

Positive rate of each IGRA was 25.9% (15/58) in QuantiFERON TB-Gold (QFT-G), 31.8% (7/22) in QuantiFERON-TB Gold In Tube (QFT-GIT), and 33.3% (7/21) in T-SPOT. TB (T-SPOT). After excluding cases having a history of tuberculosis, positive rate of each IGRA decreased to 19% (8/42) in QFT-G, 20% (3/15) in QFT-GIT, and 18.8% (3/16) in T-SPOT. The multivariate analysis revealed that only previous tuberculosis was significantly associated with positive IGRAs (odds ratio, 4.758; 95% confidence interval, 1.73-13.05; p = 0.002).

CONCLUSIONS

Positive rates of IGRAs were low in patients with M. kansasii, especially in those without previous tuberculosis. M. kansasii pulmonary infection alone might induce less interferon-gamma production with the antigens.

Screening of latent tuberculosis infection by interferon-γ release assays in rheumatic patients: a systemic review and meta-analysis

The aim of this study is to assess the diagnostic value of interferon-γ release assays (IGRAs) for latent tuberculosis infection (LTBI) in patients with rheumatic disease before receiving biologic agents. MEDLINE and EMBASE databases were used for searching studies concerning the evaluation on the performance of IGRAs [QuantiFERON-TB Gold (QFT-G), QuantiFERON-TB Gold In-Tube (QFT-GIT) and T-SPOT.TB] in rheumatic patients before biological therapy. After assessing the quality of all studies included in the review, we summarized the results in subgroups using forest plots and calculated pooled estimates if applicable. The search identified 11 studies with a total sample size of 1940 individuals. Compared with the tuberculin skin test (TST), the pooled agreements in QFT-G/GIT and T-SPOT.TB were 72 % (95 % confidence interval (CI) 65, 78 %) and 75 % (95 % CI 67, 83 %), respectively. BCG vaccination was positively correlated with positive rates of TST (pooled odds ratio (OR) 1.64, 95 % CI 1.06, 2.53). Compared with TST, IGRAs were better associated with the presentence of one or more tuberculosis (TB) risk factors. Neither steroid nor disease-modifying anti-rheumatic drugs (DMARDs) significantly affect positive IGRA results. In contrast, TST positivity was significantly impacted by the use of steroid (pooled OR 0.45, 95 % CI 0.30, 0.69), but less significantly by the use of DMARDs (pooled OR 0.78, 95 % CI 0.50, 1.21). In conclusion, in rheumatic patients with previous BCG vaccination or currently on steroid therapy, IGRAs would be the better choice to identify LTBI by decreasing the false-positivity and false-negativity rate compared with conventional TST.

Cytokine and chemokine expression profiles in response to Mycobacterium tuberculosis stimulation are altered in HIV-infected compared to HIV-uninfected subjects with active tuberculosis

Mycobacterium tuberculosis (Mtb) infects nearly 2 million people annually and is the most common cause of death in HIV-infected individuals. Tuberculosis (TB) diagnostics cater to HIV-uninfected individuals in non-endemic countries, are expensive, slow, and lack sensitivity for those most affected. Patterns of soluble immune markers from Mtb-stimulated immune cells are not well defined in HIV co-infection. We assessed immune differences between HIV-infected and HIV-uninfected individuals with active TB utilizing IFNγ-based QuantiFERON®-TB Gold In-Tube (QFT) testing in Nairobi, Kenya. Excess QFT supernatants were used to measure cytokine and chemokine responses by a 17-plex bead array. Mtb/HIV co-infected participants were significantly less likely to be QFT+ (47.2% versus 84.2% in the HIV-uninfected group), and demonstrated lower expression of all cytokines except for IFNα2. Receiver operator characteristic analyses identified IL-1α as a potential marker of co-infection. Among HIV-infected individuals, CD4+ T cell count correlated weakly with the expression of several analytes. Co-expression analysis highlighted differences in immune profiles between the groups. These data suggest that there is a unique and detectable Mtb-specific immune response in co-infection. A better understanding of Mtb immunology can translate into much needed immunodiagnostics with enhanced sensitivity in HIV-infected individuals, facilitating their opportunity to obtain live-saving treatment.

Does an interferon-gamma release assay change practice in possible latent tuberculosis?

BACKGROUND AND AIMS

Suspected latent tuberculosis infection (LTBI) is a common reason for referral to TB clinics. Interferon-gamma release assays (IGRAs) are more specific than tuberculin skin tests (TSTs) for diagnosing LTBI. The aim of this study is to determine if IGRA changes practice in the management of cases referred to a TB clinic for possible LTBI.

DESIGN AND METHODS

A prospective study was performed over 29 months. All adult patients who had TST, CXR & IGRA were included. The original decision regarding TB chemoprophylaxis was made by TB team consensus, based on clinical history and TST. Cases were then analysed with the addition of IGRA to determine if this had altered management. An independent physician subsequently reviewed the cases.

RESULTS

Of 204 patients studied, 68 were immunocompromised. 120 patients had positive TSTs. Of these, 36 (30%) had a positive QFT and 84 (70%) had a negative QFT. Practice changed in 78 (65%) cases with positive TST, all avoiding TB chemoprophylaxis due to QFT. Of the immunocompromised patients, 17 (25%) underwent change of practice. No cases of active TB have developed.

CONCLUSION

This study demonstrates a significant change of clinical practice due to IGRA use. Our findings support the NICE 2011 recommendations.

Diagnosis and management of miliary tuberculosis: current state and future perspectives

Tuberculosis (TB) remains one of the most important causes of death from an infectious disease, and it poses formidable challenges to global health at the public health, scientific, and political level. Miliary TB is a potentially fatal form of TB that results from massive lymphohematogenous dissemination of Mycobacterium tuberculosis bacilli. The epidemiology of miliary TB has been altered by the emergence of the human immunodeficiency virus (HIV) infection and widespread use of immunosuppressive drugs. Diagnosis of miliary TB is a challenge that can perplex even the most experienced clinicians. There are nonspecific clinical symptoms, and the chest radiographs do not always reveal classical miliary changes. Atypical presentations like cryptic miliary TB and acute respiratory distress syndrome often lead to delayed diagnosis. High-resolution computed tomography (HRCT) is relatively more sensitive and shows randomly distributed miliary nodules. In extrapulmonary locations, ultrasonography, CT, and magnetic resonance imaging are useful in discerning the extent of organ involvement by lesions of miliary TB. Recently, positron-emission tomographic CT has been investigated as a promising tool for evaluation of suspected TB. Fundus examination for choroid tubercles, histopathological examination of tissue biopsy specimens, and rapid culture methods for isolation of M. tuberculosis in sputum, body fluids, and other body tissues aid in confirming the diagnosis. Several novel diagnostic tests have recently become available for detecting active TB disease, screening for latent M. tuberculosis infection, and identifying drug-resistant strains of M. tuberculosis. However, progress toward a robust point-of-care test has been limited, and novel biomarker discovery remains challenging. A high index of clinical suspicion and early diagnosis and timely institution of antituberculosis treatment can be lifesaving. Response to first-line antituberculosis drugs is good, but drug-induced hepatotoxicity and drug-drug interactions in HIV/TB coinfected patients create significant problems during treatment. Data available from randomized controlled trials are insufficient to define the optimum regimen and duration of treatment in patients with drug-sensitive as well as drug-resistant miliary TB, including those with HIV/AIDS, and the role of adjunctive corticosteroid treatment has not been properly studied. Research is going on worldwide in an attempt to provide a more effective vaccine than bacille Calmette-Guérin. This review highlights the epidemiology and clinical manifestation of miliary TB, challenges, recent advances, needs, and opportunities related to TB diagnostics and treatment.

Predictors for a positive QuantiFERON-TB-Gold test in BCG-vaccinated adults with a positive tuberculin skin test

BACKGROUND

Prevention of tuberculosis (TB) in the United States usually involves testing for latent tuberculosis infection (LTBI) with a tuberculin skin test (TST), followed by offering therapy to those who have a positive test result. QuantiFERON-TB Gold assay (QFT-G) is more specific for infection with Mycobacterium tuberculosis than the TST, especially among persons vaccinated with bacillus Calmette-Guérin, thereby reducing the number of false positive tests.

METHODS

Adults referred to a pulmonary clinic for a positive TST result were tested with QFT-G. We assessed factors for having a positive QFT-G.

RESULTS

Among 100 adults who were BCG-vaccinated and had a positive TST result, 30 (30%) had a positive result using QFT-G. Persons from high-incidence countries were 8.2 times more likely to have a positive QFT-G result compared with persons from low-incidence countries (46% versus 9%). Using logistic regression to assess QFT-G positivity, strong predictors included having an abnormal chest radiograph consistent with healed TB, a TST induration of ≥16mm, and birth in a high-incidence country.

CONCLUSION

Use of QFT-G assay following a positive TST result further identifies persons who would most benefit from treatment for LTBI.

Potential role of M. tuberculosis specific IFN-γ and IL-2 ELISPOT assays in discriminating children with active or latent tuberculosis

Background

Although currently available IGRA have been reported to be promising markers for TB infection, they cannot distinguish active tuberculosis (TB) from latent infection (LTBI).

Objective

Children with LTBI, active TB disease or uninfected were prospectively evaluated by an in-house ELISPOT assay in order to investigate possible immunological markers for a differential diagnosis between LTBI and active TB.

Methods

Children at risk for TB infection prospectively enrolled in our infectious disease unit were evaluated by in-house IFN-γ and IL-2 based ELISPOT assays using a panel of Mycobacterium tuberculosis antigens.

Results

Twenty-nine children were classified as uninfected, 21 as LTBI and 25 as active TB cases (including 5 definite and 20 probable cases). Significantly higher IFN-γ ELISPOT responses were observed in infected vs. uninfected children for ESAT-6 (p<0.0001), CFP-10 (p<0.0001), TB 10.3 (p = 0.003), and AlaDH (p = 0.001), while differences were not significant considering Ag85B (p = 0.063), PstS1 (p = 0.512), and HspX (16 kDa) (p = 0.139). IL-2 ELISPOT assay responses were different for ESAT-6 (p<0.0001), CFP-10 (p<0.0001), TB 10.3 (p<0.0001), HspX (16 kDa) (p<0.0001), PstS1 (p<0.0001) and AlaDH (p = 0.001); but not for Ag85B (p = 0.063). Comparing results between children with LTBI and those with TB disease differences were significant for IFN-γ ELISPOT only for AlaDH antigen (p = 0.021) and for IL-2 ELISPOT assay for AlaDH (p<0.0001) and TB 10.3 antigen (p = 0.043). ROC analyses demonstrated sensitivity of 100% and specificity of 81% of AlaDH-IL-2 ELISPOT assay in discriminating between latent and active TB using a cut off of 12.5 SCF per million PBMCs.

Conclusion

Our data suggest that IL-2 based ELISPOT with AlaDH antigen may be of help in discriminating children with active from those with latent TB.

The role of interferon-gamma release assay in tuberculosis control

Tuberculosis is still one of the major global public health threats. Countries with low incidence must focus on exhausting the reservoir of future cases by preventing reactivation. Therefore, it is important to identify and effectively treat those individuals who have latent tuberculosis infection and who may develop active disease. The tuberculin skin test has been the standard for detection of immune response against M. tuberculosis since the beginning of the 20th century. The new millennium has brought advancement in the diagnosis of latent tuberculosis infection. The name of the new blood test is interferon-gamma release assay (IGRA). Croatia is a middle-incidence country with a long decreasing trend and developed tuberculosis control. To reach low incidence and finally eliminate tuberculosis, its tuberculosis programme needs a more aggressive approach that would include intensive contact investigation and treatment of persons with latent tuberculosis infection. This article discusses the current uses of IGRA and its role in tuberculosis control.

Temporal interferon-gamma release response to Mycobacterium kansasii infection in an anorexia nervosa patient

Due to the differences in the management of Mycobacterium kansasii disease and tuberculosis, an accurate diagnosis is required. This report, which describes what we believe to be the first documented case of M. kansasii infection in a patient suffering from anorexia nervosa, sheds light on the possible occurrence of a non-tuberculous mycobacterial infection that can mimic tuberculosis, on the risk of a misleading interpretation of interferon-gamma release assays, and on the temporal response to these tests.

The transmission of tuberculosis in schools involving children 3 to 11 years of age

Little is known about the risk of tuberculosis transmission from children. We reviewed the published literature on the transmission of tuberculosis during outbreaks involving children 3 to 11 years of age and report that transmission rates among close contacts in school outbreaks are on average higher (weighted average 69.8% vs. 39.3%) if the index case is a child than an adult.

Interferon-γ release assay in the diagnosis of latent tuberculosis infection in arthritis patients treated with tumor necrosis factor antagonists in Korea

The aim of this study was to evaluate the usefulness of the interferon-γ release assay (IGRA) for the diagnosis of latent tuberculosis infection (LTBI) in arthritis patients who received tumor necrosis factor (TNF) antagonist in Korea. The study involved 107 consecutive patients: 61 (57%) with ankylosing spondylitis and 46 (43%) with rheumatoid arthritis. Screening tests were performed including the tuberculin skin test (TST), the QuantiFERON-TB Gold In-Tube (QFT-IT) test, and chest radiography. A positive QFT-IT test result, regardless of TST results, was considered an indication for LTBI treatment. If the QFT-IT results were indeterminate, a positive TST was regarded as an indication for LTBI treatment. A Bacillus Calmette-Guérin (BCG) scar was found in 63 patients (59%). LTBI treatment was performed in 37 patients (35%), including 36 with positive QFT-IT results and one with indeterminate QFT-IT and positive TST results. No patients developed tuberculosis during a median of 18 months (range, 13-26 months) of TNF antagonist therapy. In 16 patients who had positive TST and negative QFT-IT results, TNF antagonists were given without LTBI treatment. Tuberculosis did not occur, even in these patients, during a median of 24.5 months (range, 15-33.5 months) of TNF antagonist therapy. IGRA may be used instead of TST for the diagnosis of LTBI in patients before starting TNF antagonists in countries where tuberculosis prevalence is intermediate and the BCG vaccination is mandatory at birth, such as in Korea.

[Comparative performance of QuantiFERON(®)-TB Gold IT versus tuberculin skin test among contact investigations for latent tuberculosis infection]

BACKGROUND AND OBJECTIVE

Until recently, the only tool for detection of latent tuberculosis infection (LTI) was the tuberculin skin test (PPD). QuantiFERON(®)-TB Gold In-Tube (QF), as well as other Mycobacterium tuberculosis-specific interferon-γ release assays (IGRAs), appears to be an alternative or adjunct to the PPD. The goal of the study was to compare QF with PPD to evaluate de accuracy of QF for routinely identifying LTI in contact investigations.

PATIENTS AND METHOD

We performed a descriptive and prospective study with contacts of culture-confirmed tuberculosis source cases in Bizkaia and Araba from May 2007 through February 2008 who underwent QF and PPD. Concordance between both tests was analyzed using the kappa statistic (κ).

RESULTS

376 contacts were found: 8 were high-risk children (age < 15), 30 low-medium risk children, 46 high-risk adults (age>14) and 270 low-medium risk adults. PPD was positive in 160 subjects (42.5%) at PPD ≥ 5mm, 141 (37.5%) at PPD ≥ 10mm and 95 (25.3%) at PPD ≥ 15 mm. In QF analysis 94 subjects were positive, 279 negative and 3 indeterminate. Overall agreement between QF and PPD was good at PPD ≥ 10mm (κ=0.53; p<0.0001) but agreement was poor when the index case had positive baciloscopy at PPD ≥ 5mm (κ=0.28; p<0.001) and high-risk contacts at PPD ≥ 15 mm (κ=0.048; p=0.36).

CONCLUSIONS

IGRAs are an accurate indicator of LTI, providing a more specific way of diagnostic and reducing the number of subjects to be treated. QF appears to be a valuable public health tool with potential advantages over the PPD and improving resources.

Should interferon gamma release assays become the standard method for screening patients for Mycobacterium tuberculosis infections in the United States?

The Centers for Disease Control and Prevention recently published updated guidelines for the use of interferon gamma release assays (IGRAs) to detect Mycobacterium tuberculosis. This document gives a balanced analysis of the strengths and weaknesses of IGRAs. To date, these assays have not been widely adopted in the United States by clinical laboratories. We have asked two experts, Thomas Alexander of Summa Health Care, who has adopted an IGRA for M. tuberculosis detection in his laboratory, and Melissa Miller of UNC Hospitals, who has evaluated one but has not chosen to adopt it, to explain how each reached this decision based on their experience with the test and the data that have been published concerning IGRA.

[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.

Malnutrition and helminth infection affect performance of an interferon gamma-release assay

OBJECTIVE

We sought to compare the tuberculin skin test (TST) to the QuantiFERON-TB Gold In-Tube assay (QFT-IT) and assess the effects of malnourishment and intestinal helminth infection on QFT-IT results.

METHODS

In this population-based cross-sectional study from Dhaka, Bangladesh, we screened children for latent tuberculosis infection with the QFT-IT and TST. We assess the agreement between the TST and QFT-IT, risk factors associated with indeterminate QFT-IT results, and magnitude of interferon γ (IFN-γ) production.

RESULTS

Three hundred and two children (aged 11-15.3 years) were enrolled, including 93 (30.8%) who were malnourished. Of 251 participants who provided stool samples, 117 (46.6%) were infected with Ascaris lumbricoides and/or Trichuris trichiura. TST results were positive (≥10 mm) for 101 (33.4%) children and negative for 201 (66.6%) children. QFT-IT results were positive for 107 (35.4%) children, negative for 121 (40.1%) children, and indeterminate for 74 (24.5%) children. Agreement between the tests was moderate (κ = 0.55 [95% confidence interval: 0.44-0.65]; P < .0001) when excluding indeterminate results. Children with indeterminate QFT-IT results were separately compared with children with positive and negative QFT-IT results; malnutrition (P = .0006 and .0003), and helminth infection (P = .05 and .02), and the statistical interaction between these 2 terms (P = .03 and .004) were associated with indeterminate results. Higher levels of IFN-γ in response to tuberculosis antigens were associated with positive TST results (P < .0001); lower levels were associated with malnutrition (P = .02).

CONCLUSIONS

Malnutrition and helminth infections were associated with indeterminate QFT-IT results. Therefore, the presence of such conditions may limit the interpretability of QFT-IT results in children.

Performance of a Whole-Blood Interferon-Gamma Release Assay with Mycobacterium RD1-Specific Antigens among HIV-Infected Persons

OBJECTIVE

To evaluate the usefulness of one of IGRAs, QuantiFERON-TB Gold (QFT-G), in human immunodeficiency virus- (HIV-) infected patients with various CD4(+) T cell counts.

METHODS

The QFT-G assay was performed using QFT-G kits among 107 HIV-infected patients including 9 cases with active tuberculosis (TB).

RESULTS

In HIV-infected patients with CD4(+) > 50/microL, QFT-G positive rate for active TB patients was 5/6 (sensitivity = 83%), and that for those without active disease was 1/69 (specificity = 99%). The frequency of indeterminate QFT-G test was significantly higher in those with CD4(+) less than 50/microL (P < .0001). At the same time there was a proportional relationship between CD4(+) and interferon-gamma response to mitogen (positive control) in QFT-G test (P = .0001). Conclusions. Our data suggested that QFT-G had high sensitivity and specificity in HIV-infected populations with CD4(+) greater than 50/microL. However, QFT-G did not perform well in HIV-positive patients with CD4(+) less than 50/microL.

Clinical utility of the QuantiFERON-TB Gold In-Tube test for the diagnosis of active pulmonary tuberculosis

We evaluated the usefulness of interferon-gamma release assays (IGRAs) in the diagnosis of active tuberculosis (TB) in routine clinical practice. We retrospectively assessed the diagnostic usefulness of the QuantiFERON-TB Gold In-Tube (QFT-IT) test in 519 consecutive patients who were suspected of having active pulmonary TB and had QFT-IT test results. Active pulmonary TB was diagnosed in 242 patients (47%). The sensitivity in the diagnosis of active pulmonary TB was higher with the QFT-IT test (84%) than with the tuberculin skin test (TST; 74%; p=0.003). The negative predictive value in the diagnosis of active pulmonary TB was also higher with the QFT-IT test (79%) than with the TST (70%; p=0.023). Among 59 patients with non-tuberculous mycobacterial lung disease, the QFT-IT test was positive in 29 patients (49%). In conclusion, the high negative predictive value of the QFT-IT suggests a supplementary role for this test in the diagnostic exclusion of active TB. However, negative QFT-IT test results should not be used alone to exclude active TB. Additionally, the QFT-IT test has limited usefulness in differentiating active pulmonary TB from non-tuberculous mycobacterial lung disease in areas with a high prevalence of latent tuberculosis infection.

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.