[COMPARISON BETWEEN QFT-3G AND T-SPOT IN THE CONTACT INVESTIGATION OF A TUBERCULOSIS OUTBREAK].

Purpose: We experienced a tuberculosis outbreak in a business establishment. Contact investigation was carried out using both the QFT-3G and T-SPOT tuberculosis (TB) tests on the same subjects and the test results were compared.

Method: The QFT-3G and T-SPOT tests were performed simultaneously at three time points during the contact inves- tigation, so just after tuberculosis registration (n =14), at 3 months post registration (n=24), and at 2 years post regis- tration (n=22). Chest radiography was also performed for all subjects (n = 3 1) just after the registration.

Results: From the contact investigation results, 2 cases of pulmonary tuberculosis and 14 of latent tuberculosis infection (LTBI) were detected. It was considered that the TB infection rate was high in the investigated group. The QFT-3G and T-SPOT positive rates, respectively, were 71 % (10/14) and 29% (4/14) just after registration, 38% (9/24) and 4% (1/24) at 3 months post registration, and 27% (6/22) and 5% (1/22) at 2 years post registration, and deviated from each other significantly (concordance rate, Ic 0.16 - 0.27). The positive rate of QFT-3G was significantly higher than that of T-SPOT, and QFT-3G could detect TB infection earlier than T-SPOT. The differences of test characteristics had no little impact on the diagnostic rate of LTBI.

Discussion: It is important that the diagnosis and treat- ment of LTBI be evaluated in a comprehensive manner, after considering test characteristics of the interferon-gamma release assay and epidemiological information of TB.