Celia Milà

Comparison of Two Commercially Available Gamma Interferon Blood Tests for Immunodiagnosis of Tuberculosis

ABSTRACT We evaluated the T-SPOT.TB and Quantiferon-TB Gold In tube (QFN-G-IT) tests for diagnosing Mycobacterium tuberculosis infection. T-SPOT.TB was more sensitive than QFN-G-IT in diagnosing both active and latent infection. Both gamma interferon tests were unaffected by prior Mycobacterium bovis BCG vaccination. Among children who were not BCG vaccinated but had a positive tuberculin skin test, QFN-G-IT was negative in 53.3% of cases, and T-SPOT.TB was negative in 50% of cases.

T-cell responses to the Mycobacterium tuberculosis-specific antigens in active tuberculosis patients at the beginning, during, and after antituberculosis treatment.

The objectives of the study were to assess the performance of the QuantiFERON-TB Gold In-Tube (QFN-G-IT) and the T-SPOT.TB tests in the immunodiagnosis of active tuberculosis (TB) in adult patients, and to study the T-cell interferon gamma (IFN-gamma) responses during treatment and in patients who have recovered after curative treatment and self-healed TB patients. When only analyzing patients included at the beginning of treatment, the sensitivity was 83.3% for T-SPOT.TB and 69.4% for QFN-G-IT. In contrast, when evaluating patients during treatment, the sensitivity of the T-SPOT.TB and QFN-G-IT decreased to 69.8% and 48.8%, respectively. The response to the specific antigens increased after finishing the treatment compared with the values during the treatment. The T-SPOT.TB was more sensitive in diagnosing active TB than the QFN-G-IT. The IFN-gamma tests could be used as a complementary method in the diagnosis of active TB.

Diagnosing TB infection in children: analysis of discordances using in vitro tests and the tuberculin skin test

The aim of the present study was to compare the performance of the interferon (IFN)-&ggr; tests (QuantiFERON®-TB Gold In-Tube (QFT-G-IT) and T-SPOT®.TB) with the tuberculin skin test (TST) in diagnosing tuberculosis (TB) infection in children, and to analyse discordant results. This was a prospective study including 98 children from contact-tracing studies and 68 children with TST indurations ≥5 mm recruited during public health screenings. Positive IFN-&ggr; tests results were associated with risk of exposure (p<0.0001). T-SPOT.TB was positive in 11 (78.6%) out of 14 cases with active TB and QFT-G-IT in nine (64.3%) out of 14 cases. Sensitised T-cells against Mycobacterium avium were detected in six out of 12 children not vaccinated with bacille Calmette-Guérin (BCG), a TST induration 5–9 mm in diameter and both IFN-&ggr; tests negative. In concordant IFN-&ggr; tests results, a positive correlation was found (p = 0.0001) between the number of responding cells and the amount of IFN-&ggr; released. However, in discordant IFN-&ggr; tests results this correlation was negative (p = 0.371): an increase in the number of spot-forming cells correlated with a decrease in the amount of IFN-&ggr; released. The use of IFN-&ggr; tests is helpful for the diagnosis of TB infection, avoiding cross-reactions with BCG immunisation and nontuberculous mycobacterial infections. The analysis of highly discordant results requires further investigation to elucidate possible clinical implications.

Immunogenicity of 60 novel latency-related antigens of Mycobacterium tuberculosis

The aim of our work here was to evaluate the immunogenicity of 60 mycobacterial antigens, some of which have not been previously assessed, notably a novel series of in vivo-expressed Mycobacterium tuberculosis (IVE-TB) antigens. We enrolled 505 subjects and separated them in individuals with and without latent tuberculosis infection (LTBI) vs. patients with active tuberculosis (TB). Following an overnight and 7 days stimulation of whole blood with purified recombinant M. tuberculosis antigens, interferon-γ (IFN-γ) levels were determined by ELISA. Several antigens could statistically significantly differentiate the groups of individuals. We obtained promising antigens from all studied antigen groups [dormancy survival regulon (DosR regulon) encoded antigens; resuscitation-promoting factors (Rpf) antigens; IVE-TB antigens; reactivation associated antigens]. Rv1733, which is a probable conserved transmembrane protein encoded in DosR regulon, turned out to be very immunogenic and able to discriminate between the three defined TB status, thus considered a candidate biomarker. Rv2389 and Rv2435n, belonging to Rpf family and IVE-TB group of antigens, respectively, also stood out as LTBI biomarkers. Although more studies are needed to support our findings, the combined use of these antigens would be an interesting approach to TB immunodiagnosis candidates.

Predicting the Development of Tuberculosis with the Tuberculin Skin Test and QuantiFERON Testing

RATIONALE The identification of patients with latent tuberculosis infection, who are at higher risk to develop active disease, is an important component of disease control. OBJECTIVES We aim to compare the usefulness of the QuantiFERON-TB Gold in-tube assay and the tuberculin skin test to predict the development of active tuberculosis during follow-up, using positive and negative predictive values, positive likelihood ratios, and stratified level of risk. METHODS The study included contacts of tuberculosis cases diagnosed between 2007 and 2009. All contacts included were from the first circle of exposure. Tuberculin skin test and QuantiFERON test were performed and a chest radiograph was obtained during the contacts study. MEASUREMENTS AND MAIN RESULTS A total of 1,335 contacts were followed up for 4 years: a smear-positive index case was identified for 937 contacts, of whom 15 developed active tuberculosis and had initially presented with positive tuberculin skin test/QuantiFERON results, a normal chest radiograph, and no symptoms. The positive predictive value was 4% for QuantiFERON and 2% for the tuberculin skin test (when ≥5 mm). The probability of developing active disease was 2.36 times higher with a positive QuantiFERON, and 1.3 times higher with a positive tuberculin skin test. The positive predictive value was 17%, and the positive likelihood ratio was 7.53 for untreated contacts with a positive QuantiFERON. Stratifying according to initial QuantiFERON results showed a 6.36 times higher risk of developing active tuberculosis for patients with a QuantiFERON result greater than or equal to 10 IU/ml. Among bacillus Calmette-Guérin-vaccinated patients, a tuberculin skin test induration greater than or equal to 15 mm correlated better with a positive QuantiFERON. CONCLUSIONS QuantiFERON results were more accurate than tuberculin skin test results in predicting tuberculosis. Although all contacts with QuantiFERON-positive results are at risk of developing tuberculosis, those with a tuberculin skin test induration greater than or equal to 15 mm and QuantiFERON greater than or equal to 10 IU/ml are at highest risk. This has important implications in the clinical management of tuberculosis contacts.

Assessment of the influence of direct tobacco smoke on infection and active TB management

Background Smoking is a risk factor for tuberculosis (TB) infection and disease progression. Tobacco smoking increases susceptibility to TB in a variety of ways, one of which is due to a reduction of the IFN-γ response. Consequently, an impaired immune response could affect performance of IFN-γ Release Assays (IGRAs). Objective In the present study, we assess the impact of direct tobacco smoking on radiological manifestations, sputum conversion and immune response to Mycobacterium tuberculosis, analyzing IFN-γ secretion by IGRAs. Methods A total of 525 participants were studied: (i) 175 active pulmonary TB patients and (ii) 350 individuals coming from contact tracing studies, 41 of whom were secondary TB cases. Clinical, radiological and microbiological data were collected. T-SPOT.TB and QFN-G-IT were processed according manufacturer’s instructions. Results In smoking patients with active TB, QFN-G-IT (34.4%) and T-SPOT.TB (19.5%) had high frequencies of negative results. In addition, by means of an unconditional logistic regression, smoking was a main factor associated with IGRAs’ false-negative results (aOR: 3.35; 95%CI:1.47–7.61; p<0.05). Smoking patients with active TB presented a high probability of having cavitary lesions (aOR: 1.88; 95%CI:1.02–3.46;p<0.05). Mean culture negativization (months) ± standard deviation (SD) was higher in smokers than in non-smokers (2.47±1.3 versus 1.69±1.4). Latent TB infection (LTBI) was favored in smoking contacts, being a risk factor associated with infection (aOR: 11.57; 95%CI:5.97–22.41; p<0.00005). The IFN-γ response was significantly higher in non-smokers than in smokers. Smoking quantity and IFN-γ response analyzed by IGRAs were dose-dependent related. Conclusions Smoking had a negative effect on radiological manifestations, delaying time of sputum conversion. Our data establish a link between tobacco smoking and TB due to a weakened IFN-γ response caused by direct tobacco smoke.

Monitoring changes in anti-tuberculosis treatment: associated factors determined at the time of diagnosis.

OBJECTIVES To determine predictive factors for changes in standard anti-tuberculosis chemotherapy at the time of diagnosis. METHODS A prospective study was performed among tuberculosis (TB) patients treated at specialised centres during 2008-2009. Treatment outcome was monitored per standard guidelines. Treatment was considered successful if the patient was cured or completed treatment. Factors associated with treatment modification were analysed at the bivariate and multivariate levels using logistic regression. RESULTS A total of 427 patients were included in the study. The initial standard treatment regimen was retained for 249 patients (58.3%), extended to 9 months for 36 (8.4%) and changed for 142 (33.3%). Factors associated with a change of regimen at the multivariate level were female sex, age ≥ 50 years, human immunodeficiency virus infection, comorbidities, alcoholism, hospitalisation and culture-positive sputum. Drug resistance and toxicity were analysed independently. Treatment outcome was successful in 97.2% of cases without a regimen change and in 87.3% of those with a changed regimen (P < 0.001). CONCLUSION Factors associated with changes in the initial anti-tuberculosis regimen should be considered for rigorous follow-up. Results obtained through individualised treatment provided by specialists were good despite the complexity of the cases treated.