IFNG and tuberculosis: The mean IFN-γ concentration (standard deviation [SD]) in control students, medical students, primary care doctors and nurses, and TB doctors and nurses was 1.8 (1.9) IU/ml, 4.2 (5.0) IU/ml, 7.8 (7.3) IU/ml, and 3.0 (3.6) IU/ml, respectively.