- Infection group: latent TB, TST+ ( = or > 10 mm or documented = or > 10 mm positive on medical file in the past), previously TB infected but with no active disease confirmed by chest X ray, may have received chemoprophylaxis but with no TB treatment/chemoprophylaxis within the preceding 2 years, positive QuantiFERON-TB Gold In Tube test and/or positive 6-day lymphocyte test.