Performance of QuantiFERON-TB testing in a tuberculosis outbreak at a primary school

The Risk of Mycobacterium tuberculosis Transmission from Pediatric Index Cases to School Pupils

This study is the largest report on Mycobacterium tuberculosis transmission rate (TR) from children with pulmonary tuberculosis to school pupils. Higher TR (around 21.6%) was observed in contacts of smear-positive children. TR from pediatric smear-negative index cases was around 0. If our data are confirmed, school contacts of a smear-negative index case could be screened only by clinical evaluation and tuberculin skin test, avoiding the routine use of chest radiographs in children less than 5 years of age as well.

Pediatric Tuberculosis in Northern Sardinia

Background and Objectives

Migration flux is an increasing phenomenon in Italy, and it raises several public health issues and concerns in pediatric infectious diseases. This study investigated the clinical characteristics and outcomes of a pediatric population at high-risk for tuberculosis (TB) and the potential role of immigration as a risk factor.

Design

We performed an observational retrospective study of children referred to the only Pediatric Infectious Diseases Unit for Northern Sardinia over a 6-year-period (2009–2014). Main variables assessed included TB skin test (TST), confirmed by quantiFERON Gold in Tube test, thorax X-ray (TX), microbiological culture, direct microscopy for acid-fast bacilli and molecular assays.

Results

Of the 246 children (mean age = 5.8 ± 3.9 years) identified, 222 (90.2%) were native to Sardinia and 24 (9.8%) were immigrants. The majority of children (n=205; 83%) were TB-exposed but not infected based on a negative TST and TX. Among the TST positive group (n= 39; 16%), 19 (49%) had latent TB (TX negative), while 20 (51%) had active TB (TX positive). The percent of TST positive children was significantly higher in the immigrant than the native group (42.5% versus 14%, p<0.001). Clinical presentations included pulmonary involvement with hilar lymphadenopathy (72%), pleurisy (13,5%), lateral-cervical lymphadenopathy (9%), pneumonia with calcifications (4.5%) and disseminated TB (4.5%). One child had multidrug-resistant tuberculosis.

Conclusions

Pediatric TB represents a relevant and potentially worsening public health problem in Northern Sardinia. A strict surveillance system and appropriate treatment can prevent the most severe forms and reduce TB transmission.

QuantiFERON-TB Gold Assay on Plasma for Confirmation of Presumed Tuberculosis-Related Uveitis

The QuantiFERON-TB Gold assay was used to measure interferon gamma levels in plasma from 4 patients with presumed tuberculosis-related uveitis before, during, and after antitubercular therapy. After treatment, all patients showed clinical improvement. The concentrations showed a reversion to an absence of interferon gamma in one case, decreased in two cases, and remained stable in one case. These results suggest that the QuantiFERON assay may be useful for tuberculosis-related uveitis diagnosis and follow-up.

How to manage children who have come into contact with patients affected by tuberculosis

Childhood tuberculosis (TB) indicates a recent infection, particularly in children aged < 5 years, and therefore is considered a sentinel event insofar as it highlights the presence of an undiagnosed or untreated source case. The risk of acquiring TB is directly proportional to the number of bacilli to which a subject is exposed and the environment in which the contact occurred. This document contains the recommendations of a group of Italian scientific societies for managing a child exposed to a case of TB based on an analysis of the risk factors for acquiring latent tuberculous infection (LTBI) and developing the disease, and the particular aspects TB transmission during the first years of life. The guidance includes a detailed description of the methods used to identify the index case, the tests that the exposed child should receive and the possibilities of preventive chemoprophylaxis depending on the patient's age and immune status, the chemotherapy and monitoring methods indicated in the case of LTBI, the management of a child who has come into contact with a case of multidrug-resistant or extensively drug-resistant TB, and the use of molecular typing in the analysis of epidemics. The group of experts identified risk factors for tuberculous infection and disease in pediatric age as well as gave recommendation on management of contacts of cases of TB according to their age, risk factors and exposure to multidrug-resistant or extensively drug-resistant TB.

Comparison of LCD array and IS6110-PCR with conventional techniques for detection of Mycobacterium bovis isolated from Egyptian cattle and Buffaloes

Bovine tuberculosis is a chronic bacterial and major infectious disease of cattle and buffaloes caused by Mycobacterium bovis. Rapid diagnosis of bovine tuberculosis is considered one of the cornerstones for worldwide control as it permits early epidemiological and therapeutic interventions. Therefore, this study was designed to evaluate conventional techniques (tuberculin test, Ziehl Neelsen staining and culturing) in comparison with proven molecular laboratory techniques (LCD array and IS6110 PCR) for identification of Bovine tuberculosis. A total of 902 Egyptian animals (480 buffaloes and 422 cattle) were examined by tuberculin test, and the positive reactors were slaughtered. Tissue samples were collected for staining as well as culturing. Moreover, LCD array and PCR using IS6110 on DNA extracted from tissue and culture samples were carried out for molecular identification of M. bovis. According to the results, the tuberculin positive cases for cattle and buffaloes were 2.14% (9 cases) and 5.62% (27 cases), respectively. After post-mortem examination, the prevalence of tuberculin positive cases with visible lesions was 88.9% for cattle and 14.8% for buffaloes. Alternatively, these percentages were 11.1% and 85.2% for cattle and buffalo carcasses with non-visible lesions. The percentage of cattle and buffaloes showing positive culture was 88.9% and 62.9%, respectively. This percentage was 69.5% after staining with Ziehl Neelsen. In contrast, LCD array and IS6110 were 100%, confirming the isolation results. In conclusion, LCD array depending on 16S RNA and DNA hybridization with specific probes for detection of M. bovis are rapid, sensitive and labor-saving when combined with IS6110-PCR.

Tuberculin skin test and ELISPOT/T. SPOT.TB in children and adolescents with juvenile idiopathic arthritis

BACKGROUND

There are controversies regarding the accuracy of the tuberculin skin test (TST) and methods based on the production of interferon gamma by sensitized T cells for the diagnosis of latent tuberculosis infection (LTBI) in pediatrics and immunosuppressed patients. Our objectives are to study TST and ELISPOT/T. SPOT.TB in the diagnosis of LTBI in children and adolescents with JIA undergoing methotrexate, the correlation between both and the sensitivity and specificity of T. SPOT.TB.

METHODS

This is an observational prospective longitudinal study in which children and adolescents with JIA undergoing methotrexate therapy were assessed for clinical and epidemiological data for LTBI, in addition to performing TST and T. SPOT.TB at baseline and after 3 and 12months.

RESULTS

There were 24 patients. The prevalence of LTBI at inclusion was 20.8%, the incidence after initiation of immunosuppressions 26.3% and the prevalence at the end of the study 41.6%. Epidemiological history positive for TB showed a relative risk of 2.0 for the development of LTBI. Only 2 patients had positive T. SPOT.TB but only in one it was useful for detecting early LTBI. T. SPOT.TB presented a sensitivity of 10%, specificity of 92.8%, and low correlation with TST. No patient developed TB disease at a mean follow-up of 47months.

CONCLUSIONS

We found a high prevalence of ILTB that doubled with immunosuppression and that epidemiological history was an important relative risk. T. SPOT.TB showed low sensitivity and high specificity, and no superiority over TST. There was low agreement and little influence of immunosuppression on the results of both tests.

Clinical peculiarities of tuberculosis

The ongoing spread of tuberculosis (TB) in poor resource countries and the recently increasing incidence in high resource countries lead to the need of updated knowledge for clinicians, particularly for pediatricians. The purpose of this article is to provide an overview on the most important peculiarities of TB in children. Children are less contagious than adults, but the risk of progression to active disease is higher in infants and children as compared to the subsequent ages. Diagnosis of TB in children is more difficult than in adults, because few signs are associated with primary infection, interferon-gamma release assays and tuberculin skin test are less reliable in younger children, M. tuberculosis is more rarely detected in gastric aspirates than in smears in adults and radiological findings are often not specific. Treatment of latent TB is always necessary in young children, whereas it is recommended in older children, as well as in adults, only in particular conditions. Antimycobacterial drugs are generally better tolerated in children as compared to adults, but off-label use of second-line antimycobacterial drugs is increasing, because of spreading of multidrug resistant TB worldwide. Given that TB is a disease which often involves more than one member in a family, a closer collaboration is needed between pediatricians and clinicians who take care of adults.

Interferon-γ release assays for the diagnosis of Mycobacterium tuberculosis infection in children: a systematic review and meta-analysis

Data regarding the use of interferon-gamma release assays (IGRAs) for tuberculosis diagnosis are accumulating. We systematically searched PubMed, EMBASE and Cochrane and performed pooled estimates of sensitivity and specificity of QuantiFERON-TB Gold In Tube (QFT-G-IT) and T-SPOT.TB compared to tuberculin skin test (TST). For studies assessing sensitivity, children had to have active tuberculosis. Specificity data were derived from children classified as non-infected. Eleven studies were included in the sensitivity analysis for TST, 10 for QFT-G-IT, and 9 for T-SPOT.TB. Eight studies were included in specificity analysis for TST, 8 for QFT-G-IT, and 7 for T-SPOT.TB. Pooled QFT-G-IT sensitivity was 0.79 (95% CI:0.70-0.89) pooled T-SPOT.TB sensitivity was 0.74 (95% CI:0.59-0.90) and pooled TST sensitivity was 0.82 (95% CI:0.72-0.93). Pooled QFT-G-IT and T-SPOT.TB specificities were 0.95 (95% CI:0.93- 0.97) and 0.96 (95% CI:0.93-1.00), respectively. Pooled TST specificity was significantly lower 0.83 (95% CI:0.74-0.92). IGRA performance in children showed no better sensitivity than TST, but higher specificity.

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.

[Difficulties of TB diagnosis in children: QuantiFERON TB Gold In-Tube as useful tool]

Diagnosis of childhood tuberculosis (TB), active TB or latent tuberculosis infection (LTBI), is complicated by uncommon clinical, radiological and bacteriological features. The tuberculin skin test (TST) is imperfect: difficulty of the intradermal injection for the child, lack of sensibility and specificity. The stop of the systematic inoculation by the BCG since July 2007, in France, could lead to an increase of the incidence of the childhood TB. It is urgent to find new diagnostic tools: sensitive, specific, fast, of objective reading and little expensive. Interferon-gamma assays could be useful but the data are still insufficient in paediatrics and sometimes contradictory. A prospective study which compared the usefulness of QuantiFERON TB Gold In-Tube (QFT-IT) assay with TST to detect LTBI or active disease in 51 children was realised in University Hospital of Nancy. This allowed us to confirm interest of QFT-IT; however, surprisingly, very discordant QFT-IT and TST results were obtained (only five children were QFT-IT+/TST+). A high number (14%) of indeterminate QFT-IT occurred, without explanation by pre-analytical or clinical parameters. Further studies are needed to demonstrate the usefulness of this assay in diagnosing LTBI and particularly active TB in children.

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

The specificity of the tuberculin skin test (TST) in the diagnosis of tuberculosis infection is seriously compromised because of extensive use of the bacille Calmette-Guérin (BCG) vaccination. The interferon-gamma release assay (IGRA), a new diagnostic using Mycobacterium tuberculosis-specific antigens has been introduced in response to these needs. In this review, published findings on the performance of the QuantiFERON-TB (QFT), one of the IGRA formats, are summarized and discussed. In addition to its high specificity, the QFT has considerably high sensitivity, comparable with or superior to that of the TST, if applied to patients with active tuberculosis as a surrogate of latent tuberculosis infection. When applied to patients with immunosuppression, such as aging patients, or those with HIV infection, those with immunosuppressive drug therapies, or those with renal hemodialysis, QFT is shown to be more robust than the TST. As regards the dynamics of QFT responses to chemotherapy, there are many reports showing a decrease in responses during the treatment, which indicates the possibility that QFT could be used as a tool for monitoring the progress of treatment. However, there are discordant reports that warrant further study.

T-cell interferon-gamma release assays for the rapid immunodiagnosis of tuberculosis: clinical utility in high-burden vs. low-burden settings

PURPOSE OF REVIEW

The utility of T-cell interferon-gamma (IFN-gamma) responses to Mycobacterium tuberculosis specific antigens [interferon-gamma release assays (IGRAs)] in high-burden settings remains unclear and there is growing evidence that IGRA performance varies across high tuberculosis (TB) burden vs. low TB burden settings. Here we review the evidence supporting the utility of IGRAs in specific subgroups and compare their performance in high-burden vs. low-burden settings.

RECENT FINDINGS

Although the IGRA, compared with the tuberculin skin test (TST), has greater specificity in BCG-vaccinated individuals, treatment of latent tuberculosis infection is not a priority in high-burden setting. Nevertheless, in high-burden settings, the TST performs reasonably well and correlates as well, or better, with proxy measures of exposure.

SUMMARY

IGRAs may still be useful in high-burden settings in specific subgroups at high risk of progression, including young children, HIV-infected individuals and healthcare workers, but this requires confirmation. Although the IGRAs cannot distinguish between latent and active TB, their utility as rule-out tests, when combined with smear microscopy or the TST, requires further study. Prospective studies are required in high-burden settings to confirm whether IFN-gamma responses are predictive of high risk of progression to active TB, particularly in HIV-infected individuals.

IFN-gamma release assays in tuberculosis management in selected high-risk populations

Tuberculosis (TB) is the most deadly infectious disease in the world. TB control relies on passive case findings and targeted treatment of latently infected individuals at high risk of disease progression. Tuberculin skin testing (TST) is conventionally used for detection of TB infection. Recently, blood assays measuring the release of IFN-gamma by TB-specific effector memory T cells have been developed to overcome TST limitations. Overall, IFN-gamma release assays are more specific than TST, more sensitive in detecting active TB and correlate better with TB exposure in immune-competent patients, at least in low-burden settings. There are three US FDA-approved assays commercially available: the ELISpot-based assay T-SPOT.TB (Oxford Immunotech, UK) and two ELISA-based formats, QuantiFERON TB Gold (QFT) and QFT-in tube (Cellestis, Australia). Recent international guidelines and consensus statements recommend the use of IFN-gamma release assays at different levels in TB management. However, conclusive evidence-based information targeting populations at high TB risk, including HIV-infected individuals, children and patient candidates for biotherapy with TNF-alpha blockers, are lacking. The aim of this review is to focus our attention on studies addressing the performance of commercial IFN-gamma release assays in clinical management of TB infection in these highly selected settings to provide a more comprehensive picture of the actual scenario and to identify areas to be investigated further.

Contact investigation in a primary school using a whole blood interferon-gamma assay

OBJECTIVES

To evaluate the usefulness of QuantiFERON-TB Gold (QFT-G) for children.

METHODS

Students in a primary school exposed to a tuberculosis patient were investigated using the tuberculin skin test (TST), chest X-ray examination and sequential QFT-G tests.

RESULTS

The first QFT-G test was conducted one month after the end of exposure for 308 of the 313 children, with 6 (1.9%) positive. TST results were obtained from 306 of the students at 2 months after exposure, and 200 (65.4%) had induration > or =5mm. A second QFT-G test, a further month later, and a third QFT-G test, six months after exposure, found an additional 2 positive and one weakly positive, respectively. Overall, the rate of QFT-G positivity was 9.8% (4/41) for close contact children (> or =90h exposure), significantly higher than for casual contacts (< or =18h exposure; 1.8%, 5/272; p=0.020), whereas there was no significant difference in TST positive rates (p=0.078).

CONCLUSIONS

These data suggest that QFT-G has the same performance characteristics in BCG vaccinated children as it does in adults. The observation that none of the 297 students who were QFT-G negative had developed active TB after 3 years of follow-up suggests that QFT-G has a very high negative predictive value.