Comparison of an interferon-gamma release assay with tuberculin skin test for the diagnosis of tuberculosis infection in a contact investigation

Abstract number: P1405

Perez-Escolano E., Gutierrez J., Menor E., Alados Arboledas J.C., López M.I., de Tena S., López-Prieto M.D.

Objectives: To evaluate the agreement of the QuantiFERON® TB Gold In Tube test (QFT) and the tuberculin skin test (TST) for the diagnosis of the tuberculosis infection (TBI) in a contact investigation (CI), and to establish the utility of QFT as a tool for the indication of the treatment of TBI.

Methods: We studied 337 immunocompetent persons with recent history of contact with tuberculosis patients and a different degree of exposition to the index case; average age was 39 years (SD: 18.6), 56.3% were women and 46% were vaccinated with BCG. All were screened with chest X-ray, TST, QFT (Cellestis, Australia) and risk factors were registered in a questionnaire. TST was performed by Mantoux method and a positive test was defined as an induration geqslant R: gt-or-equal, slanted5 mm. QTF was made according to the manufacturer specifications. We considered as vaccinated persons those presenting with a suggestive scar. CDC recommendations were followed for the interpretation of the QFT and the treatment of the TBI in contacts. Agreement between TST and QFT was assessed by the Cohen kappa coefficient.

Results: Agreement between the TST and the QFT was moderate among non-vaccinated population (74%, k0.48, CI (0.36–0.61)) and poor among the vaccinated group (40%, k0.09, CI (0.03–0.15)). Agreement was high for people with greater degree of exposure to index case, mainly in non-vaccinated group. TST(+)/QFT(-) was the most frequently detected discordant result, for vaccinated and non-vaccinated groups. A hundred eight non-vaccinated persons showed TST (+), from these 38 were negative for QTF. In the vaccinated group 132 showed TST (+), from these 92 were negative for QFT. The indication of TBI treatment made by TST and risk situation was modified in 52% of cases according to QFT test. We prescribed treatment of TBI by QFT in 8% of the contacts that did not have indication according to the TST.

Conclusions: Agreement between TST and QFT was moderate in non-vaccinated people and was improved in the subgroup with more than six hours/day of exposure to index case. Whereas, in vaccinated people the agreement was poor. The use of QFT allows to a better selection of infected individuals and to reduce the number of unnecessary treatments of the TBI, particularly in vaccinated population.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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