In two previous studies (10, 11), an antigen tube 2 minus antigen tube 1 (TB2−TB1) value >0.6 IU·ml−1 in contacts was associated with sleeping in the same room as index cases and with European origin (10), and a higher quantitative TB2 IFN-γ response was found in contacts living in the same room as index cases (11), data highly suggestive of newly acquired infection. This evidence concerns the gene IFNG and infection.