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

[Tuberculosis screening program for undocumented immigrant teenagers using the QuantiFERON(®)-TB Gold In-Tube test]

BACKGROUND AND OBJECTIVE

The aim of this study was to determine the prevalence of tuberculosis infection in undocumented immigrant teenagers using a tuberculin skin test (TST) for initial screening and QuantiFERON(®)-TB Gold In-Tube (QFT-GIT) as a confirmatory test.

PATIENT AND METHOD

From 2007 to 2012, under 19 year-old immigrant teenagers from 2 accommodation centers of the Basque Country (Spain) were included in the study. The TST was done in all of them and the QFT-GIT was done in selected patients with a TST≥5mm.

RESULTS

Eight hundred and forty-five immigrants were included, most of them from Africa (99.5%). Fifty-one percent of immigrants with TST ≥ 5 mm has a positive QFT-GIT. We found 2 cases of active tuberculosis (2/845: 0.24%). The concordance between TST (≥ 10 mm) and QFT-GIT was 63%, with 57% of positive concordance cases and 96% of negative concordances. There were 246 cases with TST ≥ 10 mm (29%), with significant differences between Magrebis (21.5%) and Subsaharians (67%) (P<.001). Vaccination with Calmette-Guéin bacille was an independent predictor for having a TST ≥ 10 mm (OR: 2.11; P<.001) and for the discordance TST+/QFT-GIT-, both for a TST≥5 and a TST≥10mm (OR 2.16, 95% confidence interval [95% CI] 1.46-3.20, and OR 1.91 95% CI 1.23-2.97, respectively). The positive value of QFT-GIT increased significantly as the TST increased, with a positive association in all the cut-off points analyzed: 10-14 mm (OR 7.95, 95% CI 1.79-35.33), 15-19 mm (OR 35, 95% CI 7.93-154.52) and ≥ 20 mm (OR 91.3, 95% CI 18.20-458.11).

CONCLUSION

Due to the high prevalence of latent tuberculosis infection in Subsaharian immigrants, we recommend implementing screening programs in this population. Using QFT-GIT, the number of candidates for chemoprophylaxis was reduced to 43% compared with TST alone (≥ 10 mm).

IFN-γ production to leishmania antigen supplements the leishmania skin test in identifying exposure to L. braziliensis infection

Background

Cutaneous leishmaniasis due to L. braziliensis (CL) is characterized by a positive delayed type hypersensitivity test (DTH) leishmania skin test (LST) and high IFN-γ production to soluble leishmania antigen (SLA). The LST is used for diagnosis of CL and for identification of individuals exposed to leishmania infection but without disease. The main aim of the present study was to identify markers of exposure to L. braziliensis infection.

Methodolgy/Principal Findings

This cohort study enrolled 308 household contacts (HC) of 76 CL index cases. HC had no active or past history of leishmaniasis. For the present cross-sectional study cytokines and chemokines were determined in supernatants of whole blood culture stimulated with SLA. Of the 308 HC, 36 (11.7%) had a positive LST but in these IFN-γ was only detected in 22 (61.1%). Moreover of the 40 HC with evidence of IFN-γ production only 22 (55%) had a positive LST. A total of 54 (17.5%) of 308 HC had specific immune response to SLA. Only a moderate agreement (Kappa = 0.52; 95% CI: 0.36–0.66) was found between LST and IFN-γ production. Moreover while enhancement of CXCL10 in cultures stimulated with SLA was observed in HC with DTH+ and IFN-γ+ and in patients with IFN-γ⁺ and DTH⁻, no enhancement of this chemokine was observed in supernatants of cells of HC with DTH⁺ and IFN-γ⁻.

Conclusions/Significance

This study shows that in addition of LST, the evaluation of antigen specific IFN-γ production should be performed to determine evidence of exposure to leishmania infection. Moreover it suggests that in some HC production of IFN-γ and CXCL10 are performed by cells not involved with DTH reaction.

Both control of L. braziliensis infection and development of cutaneous leishmaniasis (CL) are dependent on the host immunological response. Due to the difficulty of finding parasites in leishmanial lesions, a delayed type hypersensitivity reaction - leishmania skin test (LST), is widely used to diagnose CL. In areas of L. braziliensis transmission a positive LST is also documented in up to 18% of individuals without disease, who are considered to be putatively resistant to leishmania infection. However the mechanisms involved in the control of parasite grow is not known. The aim of this study is to identify tests that could determine in house contact of CL (HC) without past or current evidence of leishmaniasis exposure to leishmania infection. We found that of the 308 HC, 36 (11.7%) had a positive LST but in these IFN-γ was only detected in 22 (61.1%). Moreover of the 40 HC with evidence of IFN-γ production only 22 (55%) had a positive LST. Therefore at least the two tests, the LST and IFN-γ production, should be used to determine exposure to L. braziliensis. Identification of subjects exposed to leishmania infection that may or may not develop CL is highly relevant to understand pathogenesis of L. braziliensis infection.