IFNG and infection: It is now well-established that some household or close contacts of an index case with active TB, who initially convert to a positive (QFT TB-Nil 1 and 2 values > 0.35) interferon-gamma release assay (IGRA), an indication of an Mtb-specific T cell response that reflects infection, will later revert to a negative IGRA (QFT TB-Nil 1 and 2 values < 0.35) [5].