Attack rate of tuberculosis in a 5-year period among close family contacts of tuberculous patients under domiciliary treatment with isoniazid plus PAS or isoniazid alone.

This report from the Tuberculosis Chemotherapy Centre, Madras, considers the risk, over a 5-year period, to close family contacts of sputum-positive patients treated at home for 1 year with a standard regimen of isoniazid plus PAS or one of 3 regimens of isoniazid alone. The attack rate of tuberculosis in the contacts did not appear to be influenced by the treatment received by the patients in the first year or by the duration in the 5-year period for which the patients had (1) positive sputum smears, (2) positive cultures, or (3) isoniazid-resistant cultures. Further, over half the cases of tuberculosis developed in the first year, many of these being in the first 3 months. These findings confirm the conclusions reached from an earlier study, namely, that the major risk to the contacts is from exposure to the infectious patient before diagnosis, and that the risks from the other possible sources of infection (the patient during treatment and the urban environment of Madras) are, in comparison, small.