- Infection group: Known to be treated for latent TB, PPDpositive (equal or over 10 mm or documented equal or over 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.