On the other hand however, a study evaluating the use of the IFN-γ assay and the TST as screening tools in Australian children at high risk of TB reported that IGRAs were negative in 70% of children with positive TSTs, [38] and a study among a paediatric population in the USA reporting similar levels of IGRA-/TST+ discordance (79% in BCG-vaccinated or foreign-born children, 37% in US-born children) [40]. This evidence concerns the gene IFNG and tuberculosis.