[Validity of "the risk index" to predict the infectiousness of tuberculosis patients]

It has been proposed that "the risk index" obtained by multiplying the score of sputum-smear examination (Gaffky number) by the duration of symptomatic period in months is useful for the prediction of the infectiousness of a tuberculosis patient. To verify this theory, contacts examination of 498 index cases, who were newly registered by the Kochi Chuo Health Center from 1986 to 1988 as pulmonary tuberculosis patients, was carried out. Of the index cases, 58 cases (11.6%) were suspected to be responsible for significantly strong tuberculin reactions of one or more persons among their respective contacts. The proportion of such infectious cases was higher among the smear-positive index cases as well as those with cough, in comparison with smear-negative ones and those without cough. The rate of infectious case rose significantly according to the rank of "the risk index" of the index case. From these results, it was concluded that "the risk index" was useful to predict the infectiousness of the tuberculosis patients.