[A study on family infection of tuberculosis]

The guideline for contacts examination and chemoprophylaxis for tuberculosis was revised in 1993. Secondary cases and chemoprophylaxis cases found by the contacts examination of family members were analyzed in Sapporo City. The average age of index cases and of secondary cases has become higher. Many secondary cases were found among spouse of the index case and children of male index case. Chemoprophylaxis cases were found mostly among children of male or female index cases and grandchildren of male index cases. The results of family contacts examination carried out during the period from 1994 to 1999 were compared with those from 1987 to 1992. The incidence of family infection of tuberculosis and the number of newly infected persons and of secondary cases have decreased in the latter period. The time interval from the registration of the index case to the detection of secondary cases has become shorter, and the ratio of sputum smear positive cases among secondary cases has also decreased. Male to female ratio of the index cases was 2:1, that of secondary cases was 3:5, and that of children indicated chemoprophylaxis was 4:5. All secondary cases found by the contacts examination carried out within 6 months after the previous examination were sputum smear negative for tubercle bacilli, and there were a few smear positive cases among secondary cases who were found by the examination with longer interval with the previous examination. Such cases with longer interval from the last periodic examination was found often among younger cases below 40 years of age. Most smear negative tuberculosis cases were found by the family contacts examination, while most smear positive cases were found by symptomatic visit to doctors.