Use of tuberculin skin test, IFN-γ release assays and IFN-γ-induced protein-10 to identify children with TB infection.

Current tests of tuberculosis (TB) infection (tuberculin skin test (TST), interferon (IFN)-γ-release assays (IGRAs) and IFN-γ-induced protein (IP)-10) have limitations and their value when used consecutively to identify infected children has not been explored. This study describes TST, IGRA and IP-10 responses in children in contact with adults with TB, the agreement of the tests and whether using multiple tests indentifies more infected children. 330 children (aged 1-15 yrs) in contact with adults with pulmonary TB and 156 controls were studied in Ethiopia. Children exposed to adults with high bacilli grades in sputum were more likely to have positive TST, IFN-γ and IP-10 than controls. The agreement of positive tests was directly associated with the sputum bacilli grades (p<0.001 for all). The agreement of negative tests was higher in control children. The consecutive use of the tests increased the number of children classified as having at least one positive test. Using three tests increases the number of children classified as infected. This increase is associated with the bacilli load of the adults. Using only one test may underestimate the proportion of infected children, but the interpretation of the data is difficult due to the lack of reference standards.