In Canada: a trial of chemoprophylaxis in inactive tuberculosis.

One thousand five hundred and thirty-six patients with inactive tuberculosis were given a course of preventive treatment consisting of either INH alone or INH and PAS while 840 similar patients served as a control group. Discontinuation of the treatment was frequent and was usually caused by development of complaints which the patients ascribed to the drugs they were taking.The annual reactivation rate among controls was 4.9 per 1000. During the period of taking drugs the treated group suffered a reactivation rate of 0.7 per 1000 and those who had taken the medication for at least six months suffered a subsequent annual reactivation rate of 1.3 per 1000. The rate for those who discontinued treatment in the first six months was 5.1 per 1000. There were no reactivations in patients who took INH and PAS for over six months. Bacilli from two of the patients with reactivations who were treated for a prolonged period with INH alone showed resistance to this drug.Chemoprophylaxis of inactive cases is a potent weapon in tuberculosis control; however, it requires thorough motivation and supervision.