Abstract
A trial of prophylactic isoniazid among household contacts of previously diagnosed cases of tuberculosis was undertaken by the Tuberculosis Program of the Public Health Service as a pilot study to develop procedures used in the trial among contacts of newly diagnosed cases. The trial, carried out in co-operation with 5 health departments, included 2814 contacts: 1351 who received placebo and 1463 who received isoniazid. The average daily dose was 5 mg per kg, prescribed for one year. Nearly 2/3 of the participants took at least 3/4 of their assigned pills. Only 3 persons assigned isoniazid developed active tuberculosis during the year compared with 9 among those taking placebo, 8 of whom reacted to tuberculin at the start of the trial. During 3 years of observation after the year of medication, 3 cases of tuberculosis became known in each group. In this period, only 2 persons among the original 2814 contacts have been lost to observation.

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