QuantiFERON®-TB Gold test in the identification of latent tuberculosis infection in immigrants

Background: The identification and treatment of latent tuberculosis infection (LTBI) among immigrants are an effective strategy for TB control in developed countries. A new test for LTBI identification that uses more specific antigens of Mycobacterium tuberculosis is now commercially available under the brand name of QuantiFERON (R)-TB Gold test. Objective: To compare QuantiFERON (R)-TB Gold test to tuberculin skin testing (TST) for the detection of LTBI among immigrants from high endemic TB areas. Patients and methods: Undocumented immigrants attending a district medical center were enrolled if they originated from high endemic TB areas, the time of arrival in Italy was <= 5 years, had neither active TB disease nor known immunodeficiency status. The TST was applied according to standards and QuantiFERON (R)-TB Gold test was performed following the manufacturer's instructions. Results: Hundred subjects were included in the comparative analysis. TST was positive in 44% of subjects; 15% had a positive QuantiFERON (R)-TB Gold test result. The total agreement between TST and QuantiFERON (R)-TB Gold test was 71%, for a k statistics of 0.37; agreement was 100% for TST negative results, but only 34% for TST positive ones. In the multivariate logistic regression analysis, previous BCG vaccination was independently associated with a tower chance of disagreement between the tests. Conclusion: The prevalence of LTBI among immigrants was lower when determined by QuantiFERON (R)-TB Gold; this may be a consequence of more specific MTB antigens used. Our results suggest that QuantiFERON (R)-TB Gold may be used as confirmatory test for TST positive immigrants candidate to preventive therapy. (c) 2007 The British Infection Society. Published by Elsevier Ltd. All rights reserved.