These two facts together, in addition to the fact that small children had probably not been previously exposed to Mtb, suggest that these individuals may be in an early phase of primary infection by Mtb. It has previously been reported that the antigens used in the Interferon-γ Release Assays ESAT-6 and CPF-10 are secreted mainly in early infection [16], [33], [34] and some studies in animals have related the initial response of primary infection to Mtb to a rapid rise in IFN-γ and a fall in ferritin values [35] suggesting a true positivization of the QFT. This evidence concerns the gene IFNG and infection.