Interferon-γ Release Assay for the Diagnosis of Latent Tuberculosis in Children Younger Than 5 Years of Age

BACKGROUND:There are limited data available on interferon-γ release assay (IGRA) performance in children up to 5 years of age, with documented exposure to active tuberculosis (TB). The aim of this study was to evaluate (1) the influence of infectivity of adult source cases on test results, (2) the impact of age, and (3) the level of agreement, between IGRA and tuberculin skin test (TST) results. METHODS:A total of 142 Bacille Calmette-Guerin-vaccinated children up to 5 years of age were investigated because of a history of exposure to active TB. QuantiFERON-TB Gold In-Tube IGRA (QFT) and TST assays were performed. RESULTS:Test results were significantly influenced by positive finding of cavitary lesions (QFT, odds ratio [OR] = 6.15; TST, OR = 7.48) and positive acid-fast bacilli (QFT, OR = 4.01; TST, OR = 4.47) in active TB contacts. QFT resulted in 1 indeterminate response (0.7%), attributable to low mitogen. There was no evidence for age having any effect on QFT performance. The 2 tests showed a moderate overall concordance (89%; κ = 0.591) at a TST cutoff value of ≥10 mm. CONCLUSIONS:Association of positive QFT and TST results with risk factors for infection in child contacts (presence of cavitary lesions and acid-fast bacilli smear positivity in index cases) suggests that both the tests have good diagnostic accuracy. However, there was significant discord between results of the 2 tests that could not be definitively resolved. Thus, in a high-risk population of children up to 5 years of age, both tests (QFT and TST) should be performed and the child should be considered infected if either or both tests are positive.