Objective: To evaluate the performance of the QuantiFERON(R)-TB Gold (QFT-G) test for screening tuberculosis (TB) contacts and estimating their risk of progressing to active TB disease.
Methods: Data on clinical progression to active disease were collected from public health centres 2 years after close contacts of TB cases had been QFT-G-tested.
Results: Among 3102 contacts observed, 419 were QFT-G-positive, and isoniazid (INH) treatment was initiated in 323. Twenty (4.8%) of these 419 developed TB disease. Among 2683 QFT-G-negative persons, 19 were diagnosed with TB (0.7%) during the average follow-up period of 1.6 years. The estimated sensitivity of QFT-G in detecting contacts who would progress to active TB was 51%, or 64% allowing for the effects of INH treatment. Among the QFT-G-negative contacts, all those who developed TB disease were contacts of highly infectious cases. Large-scale tuberculin skin testing was not available.
Conclusions: TB incidence among QFT-G-positive contacts was higher than among QFT-G-negative contacts, but the number of TB cases among QFT-G-negative contacts is non-negligible, especially among contacts of highly infectious cases.