[Primary infection and pulmonary tuberculosis]

Tuberculosis is a major public health problem worldwide. Indeed, a third of the world population is infected with Mycobacterium tuberculosis and more than 8 million new cases of tuberculosis each year. Pulmonary tuberculosis is the most common location. Its diagnosis is difficult and often established with a delay causing a spread of infection. The diagnosis of tuberculosis infection is mainly based on immunological tests represented by the tuberculin skin test and detection of gamma interferon, while the diagnosis of pulmonary tuberculosis is suspected on epidemiological context, lasting general and respiratory symptoms, contrasting usually with normal lung examination, and a chest radiography showing suggestive lesions. The radioclinical feature may be atypical in patients with extreme ages and in case of immunodeficiency. Confirmation of tuberculosis is bacteriological. Conventional bacteriological methods remain the reference. Innovative tests using the technique of molecular biology have improved the diagnosis of tuberculosis in terms of sensitivity and especially speed. However, those techniques are of limited use.

The dynamics of QuantiFERON-TB gold in-tube conversion and reversion in a cohort of South African adolescents

RATIONALE

Interferon-γ release assays are used to diagnose tuberculosis infection. In developed countries, high rates of reversion following conversion have been described.

OBJECTIVES

To assess QuantiFERON TB Gold In-Tube test (QFT) conversion and reversion dynamics in a tuberculosis-endemic setting.

METHODS

Adolescents aged 12-18 years residing near Cape Town were recruited. Tuberculin skin tests (TSTs) and QFTs were performed at baseline and after 2 years of follow up. Half of the participants had TST and QFT performed at additional time points. Participants were observed for incident tuberculosis disease for up to 5 years.

MEASUREMENTS AND MAIN RESULTS

Among 5,357 participants, 2,751 (51.4%) and 2,987 (55.8%) had positive QFT and TST results, respectively, at baseline. Annualized QFT and TST conversion risks were 14.0 and 13.0%, respectively, and reversion risks were 5.1 and 4.1%, respectively. Concordance was excellent for conversions (κ = 0.74), but poor for reversions (κ = 0.12). Among recent QFT converters, the magnitude of the QFT value was strongly inversely associated with risk of reversion (P < 0.0001). When longitudinal QFT data were analyzed in a cross-sectional manner, the annual risk of infection was 7.3%, whereas inclusion of reversions in the analysis showed that the actual risk of infection was 14.0%. Incident tuberculosis was 8-fold higher among QFT reverters than in participants with all negative QFT results (1.47 vs. 0.18 cases/100 person-years, P = 0.011).

CONCLUSIONS

In this tuberculosis-endemic setting, annual risk of infection was extremely high, whereas QFT and TST conversion concordance was higher and QFT reversion rates were lower than reported in low-burden settings.

Reducing the Rates of Indeterminate Results of the QuantiFERON-TB Gold In-Tube Test During Routine Preemployment Screening for Latent Tuberculosis Infection Among Healthcare Personnel

We implemented the QuantiFERON-TB Gold (QFT-G) In-Tube test to identify latent tuberculosis infection among potential employees prior to employment. The rates of indeterminate QFT-G In-Tube test results were higher than expected and prompted an investigation that led to successful interventions (eg, manual vortexing before incubation and the use of a modified in-tube method). The tracking of indeterminate results is suggested as an important quality control measure.

Evaluation of QuantiFERON-TB gold in-tube and tuberculin skin tests among immigrant children being screened for latent tuberculosis infection

BACKGROUND

Centers for Disease Control and Prevention requirements for pre-immigration tuberculosis (TB) screening of children 2- to 14-years old permit a tuberculin skin test (TST) or an interferon-gamma release assay (IGRA). Few data are available on the performance of IGRAs versus TSTs in foreign-born children.

METHODS

We compared the performance of TST and QuantiFERON-TB (QFT) Gold In-Tube in children 2- to 14-years old applying to immigrate to the United States from Mexico, the Philippines and Vietnam, using diagnosis of TB in immigrating family members as a measure of potential exposure.

RESULTS

We enrolled 2520 children: 664 (26%) were TST+ and 142 (5.6%) were QFT+. One hundred and eleven (4.4%) were TST+/QFT+, 553 (21.9%) were TST+/QFT- and 31 (1.2%) were TST-/QFT+. Agreement between tests was poor (κ = 0.20). Although positive results of both tests were significantly associated with older age (relative risks [RR] TST+, 1.64; 95% confidence interval [CI]: 1.36-1.97; RR QFT+, 3.05; 95% CI: 1.72-5.38) and with the presence of TB in at least 1 immigrating family member (RR TST+, 1.40; 95% CI: 1.12-1.75; RR QFT+ 2.24; 95% CI: 1.18-4.28), QFT+ results were more strongly associated with both predictive variables.

CONCLUSIONS

The findings support the preferential use of QFT over TST for pre-immigration screening of foreign-born children 2 years of age and older and lend support to the preferential use of IGRAs in testing foreign-born children for latent TB infection.

[A positive test QuantiFERON-TB Gold In-Tube in a patient treated with continuous ambulatory peritoneal dialysis]

Patients undergoing renal replacement therapy have a higher risk of developing tuberculosis (TBC) in comparison with normal renal function population. The anergy to the tuberculin skin test, the lack of characteristic clinical symptoms of TBC and typical radiographic signs, and high prevalence of extrapulmonary TBC make the diagnosis in dialysis patients difficult and often delay the treatment. In contrast to the active TBC, latent TBC infection (LTBI) is asymptomatic and is not a direct epidemiological problem. However, in patients with end-stage renal disease prepared for renal transplantation, it is an obstacle to qualifying for immunosuppressive therapy. Treatment of LTBI patients with antimycobacterial medication decreases about 90% risk of developing active TB. Therefore, the possibility of a fast and easy identification of LTBI in this group of patients is extremely important. Test QuantiFERON-TB Gold In-Tube (QFT-G) is a new, simple and rapid diagnostic tool in LTBI and active tuberculosis infection (in conjunction with previously used clinical and microbiological methods). This test has been approved and is used in many European countries and in the USA. In a 65-year old patient, treated for 5 years with continuous ambulatory peritoneal dialysis, positive QFT-G results were shownin the course of diagnosis before reporting to the transplant program. After conducting an extensive diagnosis for tuberculosis infection (epidemiological interview, clinical examination, imaging studies, cultures by MB/BacT and the conventional method, consultations with a pulmonologist), latent form of tuberculosis was diagnosed with unspecified location. Due to the positive QFT-G and the need for future immunosuppressive treatment after kidney transplantation, a three-month prophylactic treatment with Rifamazyd 450 mg per day was included. After treatment, the patient entered the waiting list for a kidney transplant. Test QFT-G, in conjunction with other conventional methods is a good and rapid diagnostic tool in the identification of LTBI.

The feasibility of the interferon gamma release assay and predictors of discordance with the tuberculin skin test for the diagnosis of latent tuberculosis infection in a remote Aboriginal community

Background

The tuberculin skin test (TST) is the standard test used to screen for latent TB infection (LTBI) in the northern Canadian territory of Nunavut. Interferon gamma release assays (IGRA) are T cell blood-based assays to diagnose LTBI. The Bacillus Calmette-Guerin (BCG) vaccine is part of the routine immunization schedule in Nunavut. The objective of this study was to test the feasibility, and predictors of discordance between the Tuberculin Skin Test (TST) and the IGRA assay in a medically under-serviced remote arctic Aboriginal population.

Methods

Both the TST and QuantiFERON-TB Gold (Qiagen group) IGRA tests were offered to people in their homes as part of a public health campaign aimed at high TB risk residential areas in Iqaluit, Nunavut, Canada. Feasibility was measured by the capacity of the staff to do the test successfully as measured by the proportion of results obtained.

Results

In this population of predominantly young Inuit who were mostly BCG vaccinated, the use of IGRA for the diagnosis of LTBI was feasible. IGRA testing resulted in more available test results reaching patients (95.6% vs 90.9% p = 0.02) but took longer (median 8 days (IGRA) vs 2 days (TST), p value <0.0001). 44/256 participants (17.2%) had discordant results. Multivariable regression analysis suggested that discordant results were most likely to have received multiple BCG vaccinations (RR 20.03, 95% CI, 3.94–101.82)), followed by BCG given post infancy (RR 8.13, 95% CI, 2.54–26.03)) and then to a lesser degree when BCG was given in infancy (RR 6.43, 95% CI, 1.72–24.85).

Interpretation

IGRA is feasible in Iqaluit, Nunavut, a remote Arctic community. IGRA testing results in more test results available to patients compared to TST. This test could result in fewer patients requiring latent TB treatment among those previously vaccinated with BCG in a region with limited public health human resources.

Evaluation of extra pulmonary tuberculosis in Bangladeshi patients

This is a retrospective study of 200 cases of Extra Pulmonary Tuberculosis (EPTB) and this study was conducted from January 2010 to July 2011 at Sheheed Ziaur Rahman Medical College Hospital and TB clinic, Bogra, Bangladesh. Data were collected from the Hospital records on demographics, clinical, laboratory and treatment out come status. The incidence of EPTB was high in 16-45 years age group (55%), mean age was 35.67±14.6 years and predominated in Female patients (60%). Extra pulmonary Tuberculosis (EPTB) still constitutes an important clinical problem in Bangladesh. The objective of this study was to evaluate the demography and features of patients with EPTB in our high burden tuberculosis country. Lymph nodes are the most common site of involvement (50%) followed by tubercular pleural effusion (15%) and virtually every site of the body can be affected by tuberculosis. Since the clinical presentation of EPTB is atypical, tissue samples for the confirmation of diagnosis can sometimes be difficult procedure and conventional diagnostic method have a poor yield, so the diagnosis is often delayed. EPTB constitutes about 15-20% of all cases of TB patients and it is more common in low socio-economic group (60%) Biopsy and/ or surgery, FNAC is required to procure tissue samples and pus and/or aspirated fluids are required for diagnosis and for managing complications. The EPTB usually responds to standard anti tubercular drug regimen.

Development of a POC test for TB based on multiple immunodominant epitopes of M. tuberculosis specific cell-wall proteins

The need for an accurate, rapid, simple and affordable point-of-care (POC) test for Tuberculosis (TB) that can be implemented in microscopy centers and other peripheral health-care settings in the TB-endemic countries remains unmet. This manuscript describes preliminary results of a new prototype rapid lateral flow TB test based on detection of antibodies to immunodominant epitopes (peptides) derived from carefully selected, highly immunogenic M. tuberculosis cell-wall proteins. Peptide selection was initially based on recognition by antibodies in sera from TB patients but not in PPD-/PPD+/BCG-vaccinated individuals from TB-endemic settings. The peptides were conjugated to BSA; the purified peptide-BSA conjugates striped onto nitrocellulose membrane and adsorbed onto colloidal gold particles to devise the prototype test, and evaluated for reactivity with sera from 3 PPD-, 29 PPD+, 15 PPD-unknown healthy subjects, 10 patients with non-TB lung disease and 124 smear-positive TB patients. The assay parameters were adjusted to determine positive/negative status within 15 minutes via visual or instrumented assessment. There was minimal or no reactivity of sera from non-TB subjects with the striped BSA-peptides demonstrating the lack of anti-peptide antibodies in subjects with latent TB and/or BCG vaccination. Sera from most TB patients demonstrated reactivity with one or more peptides. The sensitivity of antibody detection ranged from 28–85% with the 9 BSA-peptides. Three peptides were further evaluated with sera from 400 subjects, including additional PPD-/PPD+/PPD-unknown healthy contacts, close hospital contacts and household contacts of untreated TB patients, patients with non-TB lung disease, and HIV+TB- patients. Combination of the 3 peptides provided sensitivity and specificity>90%. While the final fully optimized lateral flow POC test for TB is under development, these preliminary results demonstrate that an antibody-detection based rapid POC lateral flow test based on select combinations of immunodominant M. tb-specific epitopes may potentially replace microscopy for TB diagnosis in TB-endemic settings.

[The evaluation of the utility of QuantiFERON TB-Gold In-Tube; QFT-GIT]

Four years has passed since QuantiFERON TB-Gold In-Tube (QFT-GIT), the third generation test, has replaced QuantiFERON-Gold in Japan. The QFT-GIT test detects interferon-gamma (IFN-γ), which is released from lymphocytes present in blood after exposure to the M. tuberculosis complex antigens ESAT-6, CFP-10 and TB7.7. These proteins are absent from all Bacille-Calmette-Guérin (BCG) strains and from most non-tuberculosis mycobacteria, resulting in fewer false positive reactions as seen with the tuberculin skin test (TST). We had various experiences with QFT-GIT during these four years. So, we discussed the usefulness and its limitation of QFT-GIT as follows: 1. Development of the principle of QuantiFERON-GIT: Nobuyuki HARADA (Research Institute of Immune Diagnosis (RIID)). QuantiFERON (QFT) was originated from diagnostic system for bovine in Australia. Although the first generation of QFT, in which PPD had been used as stimulating antigens, was approved in USA, its diagnostic value was not recognized in Japan where most of Japanese are vaccinated with BCG. By combining M. tuberculosis-specific antigens with QFT system, the second generation of QFT, QFT-Gold, was developed, and approved in Japan in 2005. QFT-Gold was soon incorporated in several guidelines such as contact investigations and nosocomial infection measures. Now, QFT-Gold was superseded by the improved QFT-Gold, the current QFT-GIT. However, since QFT-GIT may contain unstable factors including blood volume and shaking methods of blood collection tubes, development of the more improved version is strongly expected. 2. Evaluating the result of QFT-GIT in patients treated with dialysis and immunosuppressive agents: Hidetoshi IGARI (National Hospital Organization Chiba-East National Hospital) The effectiveness of QuantiFERON TB-Gold In-Tube was analyzed in the patients with chronic kidney disease (CKD) and rheumatoid arthritis (RA). QFT positive was 7% and 11% respectively, and indeterminate was 5% and 2% respectively. QFT positive was 2% in hemodialysis patients, significantly lower than that of CKD. QFT positive after biological drug was administered was 8% in RA patients, significantly lower than 15% of RA without biological drug. The rate of latent tuberculosis patients in CKD was as well as health care workers (HCWs) of 8% of QFT positive. On the other hand that of RA might be higher than HCWs. Hemodialysis and biological drug administration might attenuate QFT result with lower rate of positive. The rate of indeterminate was less than 5%. This results was improved in compared with former generation QFT. 3. QFT in Vietnam: Naoto KEICHO (Research Institute of Tuberculosis, JATA). We have promoted collaborative research on tuberculosis with Vietnamese institutes since 2002. NCGM-BMH Medical Collaboration Center plays an important role in the clinical research projects. We report 1) quality assessment of QFT for tuberculosis infection, 2) prevalence and risk factors for tuberculosis infection among hospital workers, and 3) analysis of factors lowering sensitivity of QFT for active tuberculosis. We also discuss significance of QFT in developing countries. 4. Comparison of diagnostic performances using QFT Gold and Gold In-Tube in patients with active tuberculosis: Tetsuya YAGI (Department of Infectious Diseases, Center of National University Hospital for Infection Control, Nagoya University Hospital). The goal of this study was to assess the diagnostic performances of QFT-GIT compared with QFT-Gold in patients with active tuberculosis in Nagoya University Hospital, in Japan. The sensitivity of QFT-Gold was 87.2%, the specificity of that was 77.5%. The sensitivity of QFT-GIT was 88.8%, specificity 73.2%. The performance of QFT-GIT was the same as that of QFT-Gold. The QFT-GIT tended to show higher concentration values of IFN-γ than that of QFT-Gold especially in patients with extra pulmonary tuberculosis, smear positive pulmonary tuberculosis, both lung lesion and using immunosuppressive medications. 5. Simultaneous and longitudinal comparison between QFT Gold and Gold In-Tube among health care workers; Tomoshige MATSUMOTO (Department of Clinical Laboratory Medicine, Osaka Anti-Tuberculosis Association Osaka Hospital. ex-Osaka Prefectural Medical Center for Respiratory and Allergic Diseases). The aim of this study was to compare the indeterminate rates between QFT-GIT and QFT-Gold tests. And to make longitudinal comparison by QFT-Gold assay to the same HCW. We collected blood samples by simultaneously QFT-Gold and QFT-GIT from 120 staff members in the institute who participated in this prospective comparison study. Moreover, the latest QFT-Gold test was longitudinally compared for the same 55 staff members who have received QFT-Gold before. The statistically significant difference was observed in the results of indeterminate rate between QFT-Gold and QFT-GIT using the same blood samples. It is concluded that QFT-Gold and QFT-GIT are different assays therefore it is difficult to compare QFT-Gold with QFT-GIT data on the same level. Concerning the follow-up test of the 55 people by QFT-Gold, 5 turned from positive to negative and 4 turned from indeterminate to negative. From this analysis, QFT-Gold positive subjects in the previous time have not been always positive. 6. Interpreting QFT "equivocal" results: Kenji MATSUMOTO (Osaka City Public Health Office). The participants were examined QFT-GIT test after two months to four months from last contact of smear-positive tuberculosis cases in contact investigations. We enrolled 79 contacts whose tests of QFT-GIT were equivocal results. The second QFT-GIT results were 42 negative (53.2%), 28 equivocal (35.4%) and nine positive (11.4%). 64% of the second QFT-GIT tests result in negative or positive among the first QFT-GIT equivocal contacts. When the second QFT-GIT tests were positive, it is highly probable that the contacts were infected tuberculosis and we adequately could treat latent tuberculosis infected contacts.

IGRA as a predictive factor of silent pulmonary changes in individuals following exposure to tuberculosis

OBJECTIVES

We conducted a study on usefulness of the tuberculin skin test (TST) and the Quantiferon-TB Gold IT (QFT) tests as predictors of radiological changes after contact with tuberculosis.

MATERIALS AND METHODS

The study group consisted of TB-exposed HCWs working in the Military Institute of Medicine (Warsaw, Poland). The usefulness of TST, QFT, and a combination of both tests was assessed for prediction of silent radiological findings.

RESULTS

83 previously TB-exposed participants were recruited. None of the participants had a history of active tuberculosis. Positive TST results were reported in 72 (86.8 %) participants, and positive QFTs were observed in 27 (32.5 %) cases. Chest radiographs revealed 23 findings specific for non-active tuberculosis in 18 (21.7 %) participants. The results of the QFTs were associated with the highest negative predictive value, positive predictive value, and positive likelihood ratio of silent chest X-ray findings suggestive of latent tuberculosis infection. Positive QFT was the only statistically significant variable that increases the odds ratio (OR-8.3) of the presence of typical of tuberculosis radiological changes in the lung.

CONCLUSION

A positive QFT result in an individual with no TB history who was exposed to tuberculosis in the past is associated with a significantly higher risk of clinically silent parenchymal lesions in lungs suggestive of previous tuberculosis.

[Update of the guidelines of the Israeli Association of Rheumatology for the prevention of tuberculosis in patients treated with TNF-alpha blockers]

The use of TNFalpha blockers is associated with reactivation of tuberculosis (TB). The previous guidelines of the Israeli Association of Rheumatology were based on the tuberculin skin test (TST), chest X ray and a questionnaire on possible previous exposure to TB. The growing use of Interferon-gamma released assay (IGRA) has prompted the need for an update to these guidelines. All patients who are candidates to receive TNFalpha blockers should be screened for active or Latent tuberculosis. The screening includes: Tuberculin Skin Test (TST), interferon-gamma release assays (IGRA), chest X-ray and a questionnaire about possible exposure to tuberculosis. TST > or = 10 mm is considered positive; TST < or = 5 is negative; in case of TST = 0, a 2-step screening is recommended. If TST is > or = 5 mm but < 10 mm or in heavy immunosuppressed patients with TST = 0, an IGRA test should be performed and the diagnosis of latent TB taken accordingly. If the IGRA test is indeterminate, the decision should be taken based on the TST and patient's characteristics. Patients with a TST less than 5 mm. should be questioned about prior exposure to tuberculosis. Latent tuberculosis should be treated with a 9 month course of isoniazid (300 mg/d) or a 4 month course of rifampicin (600 mg/d) or for 3 months with a combination of 300 mg. isoniazid and 600 mg. rifampicin daily. The committee recommends postponing treatment with TNFalpha blockers until completion of anti-tuberculosis therapy. If the clinical condition requires the urgent use of TNFalpha blockers, these may be initiated one month after starting treatment for latent tuberculosis.

Added value of QuantiFERON TB-gold in-tube for detecting latent tuberculosis infection among persons living with HIV/AIDS

OBJECTIVE

To evaluate the added value of QuantiFERON TB-Gold in-Tube (QTF-GIT) over the tuberculin skin testing (TST) for detecting latent tuberculosis (TB) infection (LTBI) among patients with AIDS in a city with a low TB incidence rate (11.1/100,000 inhabitants) and universal BCG coverage.

METHODS

Three hundred consecutive patients with AIDS in eight outpatient sexually transmitted disease public clinics in Brasilia were submitted to QFT-IT and TST between May 2011 and March 2013. A positive result of either test was considered to be LTBI.

RESULTS

Median CD4-cell count was 477.5 cells/mm(3); 295 (98.3%) were using antiretroviral therapy. Eighteen patients (6%, 95% CI: 3.6%-9.3%) had LTBI, of whom 4 (1.3%, 95% CI: 0.04%-2.63%) had only a positive TST, 8 (2.7%, 95% CI: 0.8%-4.5%) had only a QFT-GIT positive test, and 6 (2%, 95% CI: 0.4%-3.6%) had positive results for both tests. This represents an 81.8% relative increase in LTBI detection when QFT-GIT is added to TST. The concordance between both tests was 96% (k = 0.48).

CONCLUSIONS

The QFT-GIT alone was more effective to detect LTBI than TST alone and had an 81% added value as an add-on sequential test in this population with mild immunosuppression. The cost-effectiveness of these strategies remains to be evaluated.

A Bayesian framework for estimating the incremental value of a diagnostic test in the absence of a gold standard

BACKGROUND

The absence of a gold standard, i.e., a diagnostic reference standard having perfect sensitivity and specificity, is a common problem in clinical practice and in diagnostic research studies. There is a need for methods to estimate the incremental value of a new, imperfect test in this context.

METHODS

We use a Bayesian approach to estimate the probability of the unknown disease status via a latent class model and extend two commonly-used measures of incremental value based on predictive values [difference in the area under the ROC curve (AUC) and integrated discrimination improvement (IDI)] to the context where no gold standard exists. The methods are illustrated using simulated data and applied to the problem of estimating the incremental value of a novel interferon-gamma release assay (IGRA) over the tuberculin skin test (TST) for latent tuberculosis (TB) screening. We also show how to estimate the incremental value of IGRAs when decisions are based on observed test results rather than predictive values.

RESULTS

We showed that the incremental value is greatest when both sensitivity and specificity of the new test are better and that conditional dependence between the tests reduces the incremental value. The incremental value of the IGRA depends on the sensitivity and specificity of the TST, as well as the prevalence of latent TB, and may thus vary in different populations.

CONCLUSIONS

Even in the absence of a gold standard, incremental value statistics may be estimated and can aid decisions about the practical value of a new diagnostic test.

Tuberculin skin testing and treatment modulates interferon-gamma release assay results for latent tuberculosis in migrants

Background

Identifying latent tuberculosis infection (LTBI) in people migrating from TB endemic regions to low incidence countries is an important control measure. However, no prospective longitudinal comparisons between diagnostic tests used in such migrant populations are available.

Objectives

To compare commercial interferon (IFN)-gamma release assays (IGRAs) and the tuberculin skin test (TST) for diagnosing LTBI in a migrant population, and the influence of antecedent TST and LTBI treatment on IGRA performance.

Materials and Methods

This cohort study, performed from February to September 2012, assessed longitudinal IGRA and TST responses in Nepalese military recruits recently arrived in the UK. Concomitant T-SPOT.TB, QFT-GIT and TST were performed on day 0, with IGRAs repeated 7 and 200 days later, following treatment for LTBI if necessary.

Results

166 Nepalese recruits were prospectively assessed. At entry, 21 individuals were positive by T-SPOT.TB and 8 individuals by QFT-GIT. There was substantial agreement between TST and T-SPOT.TB positives at baseline (71.4% agreement; κ = 0.62; 95% CI:0.44–0.79), but only moderate concordance between positive IGRAs (38.1% agreement; κ = 0.46; 95% CI:0.25–0.67). When reassessed 7 days following TST, numbers of IGRA-positive individuals changed from 8 to 23 for QFT-GIT (p = 0.0074) and from 21 to 23 for T-SPOT.TB (p = 0.87). This resulted in an increase in IGRA concordance to substantial (64.3% agreement; κ = 0.73; 95% CI:0.58-0.88). Thus, in total on day 0 and day 7 after testing, 29 out of 166 participants (17.5%) provided a positive IGRA and of these 13 were TST negative. Two hundred days after the study commenced and three months after treatment for LTBI was completed by those who were given chemoprophylaxis, 23 and 21 participants were positive by T-SPOT.TB or QFT-GIT respectively. When individual responses were examined longitudinally within this population 35% of the day 7 QFT-GIT-positive, and 19% T-SPOT.TB-positive individuals, were negative by IGRA. When the change in the levels of secreted IFN-γ was examined after chemoprophylaxis the median levels were found to have fallen dramatically by 77.3% from a pre-treatment median concentration of IFN-γ 2.73 IU/ml to a post-treatment median concentration IFN-γ 0.62 (p = 0.0002).

Conclusions

This study suggests differences in the capacity of commercially available IGRAs to identify LTBI in the absence of antecedent TST and that IGRAs, in the time periods examined, may not be the optimal tests to determine the success of chemoprophylaxis for LTBI.

Effect of isoniazid therapy for latent TB infection on QuantiFERON-TB gold in-tube responses in adults with positive tuberculin skin test results in a high TB incidence area: a controlled study

BACKGROUND

T-cell interferon-γ release assays (IGRAs) are used in the diagnosis of Mycobacterium tuberculosis infection and could be useful biomarkers of response to treatment of latent TB infection for clinical trials, infection control units, and TB programs.

METHODS

This investigation was a prospective, controlled substudy of IGRA responses in 82 healthy South African adults with HIV seronegative and positive tuberculin skin test results randomly assigned to treatment with 6 months of daily isoniazid preventive therapy (IPT) or observation before Bacillus Calmette-Guérin revaccination in a clinical trial. QuantiFERON-TB Gold In-Tube (QFT-GIT) assay was used to measure interferon-γ (IFN-γ) response to mycobacterial antigens at baseline and after IPT or observation.

RESULTS

IFN-γ levels declined between baseline and the end of IPT (signed rank test P≤.0001) and between baseline and a similar period of observation without IPT (signed rank test P=.03). The rate of decrease in IFN-γ responses over time did not differ between the groups (Mann-Whitney-Wilcoxon test P=.31). QFT-GIT test results in two subjects (5%) in the IPT group and two subjects (5%) in the observation group reverted from positive to negative during follow-up. No significant difference was found between the groups with respect to baseline positivity or the proportion of patients whose tests reverted to negative.

CONCLUSIONS

IPT had no effect on changes in QFT-GIT readouts during short-term follow-up of adults with positive tuberculin skin tests in a high TB incidence setting. QFT-GIT is unlikely to be a useful biomarker of response to treatment of latent TB infection.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT01119521; URL: www.clinicaltrials.gov.

[Mycobacterium tuberculosis infection: signification, role and performance of mesure of cell-mediated immune response]

Mycobacterium tuberculosis infection: signification, role and performance of mesure of cell-mediated immune response The tuberculin skin test (TST) and IGRAs are to date the unique way to identify individuals latently infected with Mycobacterium tuberculosis. In contrast to IGRAs, test specificity of TST is clearly affected by prior vaccination with attenuated strain M. bovis (BCG). Moreover, there is evidence suggesting that the accuracy of IGRAs is higher than that of TST and therefore IGRAs should perform better to detect latent tuberculosis in immunosuppressed individuals. However, neither TST nor IGRAs permit to discriminate between latent and active infection. Furthermore, there is no available test capable to identify whether individual with latent infection harbor live or dead mycobacteria and thus to detect who is at risk to develop active tuberculosis.

Pregnancy differentially impacts performance of latent tuberculosis diagnostics in a high-burden setting

Background

Targeted screening for latent TB infection (LTBI) in vulnerable populations is a recommended TB control strategy. Pregnant women are at high risk for developing TB and likely to access healthcare, making pregnancy an important screening opportunity in developing countries. The sensitivity of the widely-used tuberculin skin test (TST), however, may be reduced during pregnancy.

Methods

We performed a cross-sectional study comparing the TST with the QuantiFERON Gold In-tube (QGIT) in 401 HIV-negative women presenting antepartum (n = 154), at delivery (n = 148), or postpartum (n = 99) to a government hospital in Pune, India. A subset of 60 women enrolled during pregnancy was followed longitudinally and received both tests at all three stages of pregnancy.

Results

The QGIT returned significantly more positive results than the TST. Of the 401 women in the cross-sectional study, 150 (37%) had a positive QGIT, compared to 59 (14%) for the TST (p<0.005). Forty-nine (12%) did not have their TST read. Of 356 who had both results available, 46 (13%) were concordant positive, 91 (25%) were discordant (12 (3%) TST+/QGIT-; 79 (22%) TST−/QGIT+), and 206 (57%) concordant negative. Comparison by stage of pregnancy revealed that QGIT percent positivity remained stable between antepartum and delivery, unlike TST results (QGIT 31–32% vs TST 11–17%). Median IFN-γ concentration was lower at delivery than in antepartum or postpartum (1.66 vs 2.65 vs 8.99 IU/mL, p = 0.001). During postpartum, both tests had significantly increased positives (QGIT 31% vs 32% vs 52%, p = 0.01; TST 17% vs 11% vs 25%, p<0.005). The same trends were observed in the longitudinal subset.

Conclusions

Timing and choice of LTBI test during pregnancy impact results. QGIT was more stable and more closely approximated the LTBI prevalence in India. But pregnancy stage clearly affects both tests, raising important questions about how the complex immune changes brought on by pregnancy may impact LTBI screening.

Variability of the QuantiFERON®-TB gold in-tube test using automated and manual methods

BACKGROUND

The QuantiFERON®-TB Gold In-Tube test (QFT-GIT) detects Mycobacterium tuberculosis (Mtb) infection by measuring release of interferon gamma (IFN-γ) when T-cells (in heparinized whole blood) are stimulated with specific Mtb antigens. The amount of IFN-γ is determined by enzyme-linked immunosorbent assay (ELISA). Automation of the ELISA method may reduce variability. To assess the impact of ELISA automation, we compared QFT-GIT results and variability when ELISAs were performed manually and with automation.

METHODS

Blood was collected into two sets of QFT-GIT tubes and processed at the same time. For each set, IFN-γ was measured in automated and manual ELISAs. Variability in interpretations and IFN-γ measurements was assessed between automated (A1 vs. A2) and manual (M1 vs. M2) ELISAs. Variability in IFN-γ measurements was also assessed on separate groups stratified by the mean of the four ELISAs.

RESULTS

Subjects (N = 146) had two automated and two manual ELISAs completed. Overall, interpretations were discordant for 16 (11%) subjects. Excluding one subject with indeterminate results, 7 (4.8%) subjects had discordant automated interpretations and 10 (6.9%) subjects had discordant manual interpretations (p = 0.17). Quantitative variability was not uniform; within-subject variability was greater with higher IFN-γ measurements and with manual ELISAs. For subjects with mean TB Responses ±0.25 IU/mL of the 0.35 IU/mL cutoff, the within-subject standard deviation for two manual tests was 0.27 (CI95 = 0.22-0.37) IU/mL vs. 0.09 (CI95 = 0.07-0.12) IU/mL for two automated tests.

CONCLUSION

QFT-GIT ELISA automation may reduce variability near the test cutoff. Methodological differences should be considered when interpreting and using IFN-γ release assays (IGRAs).

A toolbox for tuberculosis (TB) diagnosis: an Indian multi-centric study (2006-2008); evaluation of serological assays based on PGL-Tb1 and ESAT-6/CFP10 antigens for TB diagnosis

BACKGROUND

The aim of this multi-centric prospective study in India was to assess the accuracy of a serological test as an additional tool for diagnosing active tuberculosis (ATB). In particular, an assay based on ELISA using a phenolic glycolipid (PGL-Tb1) or a fusion protein (ESAT-6/CFP10) was compared to the tuberculin skin test (TST) and the microbiological results according to HIV status.

METHODS

Individuals with and without ATB and HIV infection were enrolled. Serology and TST results were analyzed per se and in combination with the microbiological data.

RESULTS

Among the 778 ATB patients, 102 were HIV-infected, 316 HIV-uninfected and 360 had an HIV-unknown status. Of the 945 non-ATB subjects, 559 were at low risk (community adults) and 386 at high risk of M. tuberculosis exposure. Among those with ATB, the sensitivity of ELISA-PGL-Tb1 for ATB was higher than that of ELISA-ESAT-6/CFP10, both in HIV-infected (72.3% versus 63.7%, p = 0.29) and HIV-uninfected/HIV-unknown groups (40.5% versus 28.6%; p<0.0001), whereas the specificity was around 91% for both tests. Sensitivity for ATB increased when the results of the two ELISA were combined, reaching 75.5% in the HIV-infected and 50.9% in the group of HIV-uninfected/HIV-unknown ATB, with a significant decrease of the global specificity (83.9%). Analyzing the ELISA results with the microbiological results, we observed that the sensitivity of both serology tests was independent of the ATB patients' smear microscopy (SM) status and grade. Combining the results of SM with both ELISA, the detection of ATB patients significantly increased (p<0.0001), particularly in those with extrapulmonary TB (up to 45.1%) or HIV infection (up to 83.3%). No significant association was observed between TST and serology results.

CONCLUSIONS

In this prospective multi-centric study, the combination of two rapid tests, such as SM and serology, might be useful in detecting ATB, especially in HIV-infected patients.

Effect of micronutrient deficiency on QuantiFERON-TB Gold In-Tube test and tuberculin skin test in diagnosis of childhood intrathoracic tuberculosis

BACKGROUND/OBJECTIVES

Data on performance of QuantiFERON-TB Gold In-Tube test (QFT) and tuberculin skin test (TST) in children with active tuberculosis from high burden countries in the context of micronutrient deficiency are scarce. The objective of this study was to evaluate the effect of micronutrient deficiency on the performance of TST and QFT in children with intrathoracic tuberculosis.

SUBJECTS/METHODS

Children with probable intrathoracic tuberculosis underwent TST, QFT, gastric lavages and induced sputum examination for AFB (Acid-Fast Bacilli) smear and culture. Zinc, copper, ferritin and vitamin D were measured on stored serum samples. The study used cross-sectional data at initiation of anti-tubercular therapy.

RESULTS

Three hundred and sixty-two children (median age 115.5 months (interquartile range: 73, 144), 200 (55.3%) girls) were enrolled in the study. Microbiological confirmation of tuberculosis could be obtained in 128 patients. TST and QFT were positive in 337 (93%) and 297 (82%) children, respectively. Performance of both the tests was unaffected by weight-for-age and height-for-age 'z-scores' or by serum copper levels. TST was not affected by serum zinc and ferritin levels. Children with negative QFT results had lower mean serum zinc level (P=0.01) and higher ferritin levels (P=0.007) as compared to those with positive test. Higher proportion of children with positive TST were vitamin D deficient/insufficient (P=0.003).

CONCLUSION

Micronutrient status, especially serum levels of zinc, may influence the performance of QFT in children with intrathoracic tuberculosis. Considering the high prevalence of zinc deficiency in developing countries, QFT should be used cautiously for diagnosing tuberculosis.

Combination of cytokine responses indicative of latent TB and active TB in Malawian adults

Background

An IFN-γ response to M. tuberculosis-specific antigens is an effective biomarker for M. tuberculosis infection but it cannot discriminate between latent TB infection and active TB disease. Combining a number of cytokine/chemokine responses to M. tuberculosis antigens may enable differentiation of latent TB from active disease.

Methods

Asymptomatic recently-exposed individuals (spouses of TB patients) were recruited and tuberculin skin tested, bled and followed-up for two years. Culture supernatants, from a six-day culture of diluted whole blood samples stimulated with M. tuberculosis-derived PPD or ESAT-6, were measured for IFN-γ, IL-10, IL-13, IL-17, TNF-α and CXCL10 using cytokine ELISAs. In addition, 15 patients with sputum smear-positive pulmonary TB were recruited and tested.

Results

Spouses with positive IFN-γ responses to M. tuberculosis ESAT-6 (>62.5 pg/mL) and TB patients showed high production of IL-17, CXCL10 and TNF-α. Higher production of IL-10 and IL-17 in response to ESAT-6 was observed in the spouses compared with TB patients while the ratios of IFN-γ/IL-10 and IFN-γ/IL-17 in response to M. tuberculosis-derived PPD were significantly higher in TB patients compared with the spouses. Tuberculin skin test results did not correlate with cytokine responses.

Conclusions

CXCL10 and TNF-α may be used as adjunct markers alongside an IFN-γ release assay to diagnose M. tuberculosis infection, and IL-17 and IL-10 production may differentiate individuals with LTBI from active TB.

Interferon Gamma Response to Combinations 38 kDa/CFP-10, 38 kDa/MPT-64, ESAT-6/MPT-64 and ESAT-6/CFP-10, Each Related to a Single Recombinant Protein ofMycobacterium tuberculosisin Individuals from Tuberculosis Endemic Areas

Several antigens of Mycobacterium tuberculosis have been identified and specificity to one or multiple antigens could determine the distinction between protective and pathogenic host reaction. Therefore T cell immune response to combinations 38 kDa/CFP-10, 38 kDa/MPT-64, ESAT-6/MPT-64 and ESAT-6/CFP-10 (each related to a single protein of Mycobacterium tuberculosis) in individuals from tuberculosis endemic areas have been examined. ELISA was used to detect IFN-gamma production in PBMC priming with single proteins and combinations in a panel of 105 individuals: 38 tuberculosis patients (6 untreated and 32 treated) and 67 healthy controls with tuberculin skin test positive or negative (TST). Brazilian TB patients highly recognized ESAT-6 (66%), but combinations improved response in the following order: ESAT-6/MPT-64 (89%) > ESAT-6/CFP-10 (73%) > 38 kDa/CFP-10 (70%), the last combination showing the highest specificity (TST(/) = 42% and TST(-) = 83%). Average IFN-gamma production in TB patients was signifi-cantly higher for 38 kDa/CFP-10 (P = 0.012) and 38 kDa/MPT-64 (P <0.035), when compared to single antigens. None of the combinations was able to discriminate TB patients from TST(+) controls; however, 38 kDa/CFP-10 displayed a borderline significance (P = 0.053). Similar to the ESAT-6/CFP-10 combination, IFN-gamma response to 38 kDa/CFP-10 showed an increased tendency in treated patients, although not signifi-cant (P = 0.16). We demonstrated for the first time that 38 kDa/CFP-10 had prediction sensitivity for TB patients similar to the ESAT-6/CFP-10 combination and also significant response improvement related to the single proteins with more selective reactivity among TST-positive individuals, which could be of potential interest for diagnostic evaluation for tuberculosis infection.