[Tuberculosis outbreak in a junior high school in Kochi City--studies on factors relating to extent of tuberculosis infection and the efficacy of isoniazid chemoprophylaxis].

A 15-year-old girl, third-grade student of a junior high school (the index case) was found to have smear-positive, cavitary pulmonary tuberculosis. Contact investigation was conducted, including tuberculin skin test and chest X-ray examinations over 700 persons. Tuberculin skin test revealed an excess of strongly-positive reactors in the third-grade students. During 2 years after the detection of the index case, a total of 31 tuberculosis patients were newly diagnosed, and out of them 8 were culture positive and restriction fragment length polymorphism (RFLP) analysis of the 8 strains and that of the index case demonstrated an identical pattern. A delay in diagnosis of the index case and poor ventilation of the classrooms were attributable to this rather large outbreak. In addition the source case seems to be highly infectious, because transmission following only sporadic contact was documented. Among the third-grade students and school staff, 129 persons were strongly-positive reactors to tuberculin skin test. Out of them one hundred five persons completed isoniazid chemoprophylaxis of recommended six months, and the others didn't receive chemoprophylaxis because most of them were aged above 30 years. All of them were followed up for 2 years after the detection of the index case, and out of 105 persons who received chemoprophylaxis, 2 cases (1.9%) were newly diagnosed as tuberculosis, while out of 24 persons without chemoprophylaxis, 6 cases (25%) developed tuberculosis.