Contact investigation in a primary school using a whole blood interferon-gamma assay

SummaryObjectivesTo evaluate the usefulness of QuantiFERON®-TB Gold (QFT-G) for children.MethodsStudents in a primary school exposed to a tuberculosis patient were investigated using the tuberculin skin test (TST), chest X-ray examination and sequential QFT-G tests.ResultsThe first QFT-G test was conducted one month after the end of exposure for 308 of the 313 children, with 6 (1.9%) positive. TST results were obtained from 306 of the students at 2 months after exposure, and 200 (65.4%) had induration ≥5 mm. A second QFT-G test, a further month later, and a third QFT-G test, six months after exposure, found an additional 2 positive and one weakly positive, respectively. Overall, the rate of QFT-G positivity was 9.8% (4/41) for close contact children (≥90 h exposure), significantly higher than for casual contacts (≤18 h exposure; 1.8%, 5/272; p = 0.020), whereas there was no significant difference in TST positive rates (p = 0.078).ConclusionsThese data suggest that QFT-G has the same performance characteristics in BCG vaccinated children as it does in adults. The observation that none of the 297 students who were QFT-G negative had developed active TB after 3 years of follow-up suggests that QFT-G has a very high negative predictive value.