 Active acute or chronic infection requiring antimicrobial therapy or serious viral infection e.g. HIV, hepatitis, herpes zoster. Patients with a reactive PPD must have completed a 6 to 12 month course of isoniazid as recommended by an infectious disease consultant. Patients with a non-reactive PPD and non-reactive anergy panel must complete a 6 to 12 month course of isoniazid if recommended by an infectious disease consultant. 