[The significance of tuberculin skin test in the investigation of mass outbreak of tuberculosis in schools].

A high school teacher was diagnosed as pulmonary tuberculosis. He was 27 years old and taught bookkeeping to the 1st year grade students in classes 3 and 6, the 2nd year grade students in classes 4 and 5. He was also the assistant teacher in charge of class 1 of the 3rd year grade students and the adviser of the badminton club in the school. He first noticed a slight cough in November 1999, and visited his physician. On December 24, he visited again for a moderate cough, fever and chill and was administered medicine and drip infusion for a cold. In the middle of January 2000, he visited another physician for a severe cough. He was referred to hospital N and was admitted due to an abnormal shadow on chest X-ray films. The result of sputum smear examination was positive for AFB, Gaffky 8. Subsequent contacts examination was conducted for 153 students and 63 teachers of the school. A tuberculin skin test survey of 153 students was also carried out, in February 2000. The diameter of erythema revealed a monomodal distribution pattern in students, however, one student was diagnosed as pulmonary tuberculosis by the chest X-ray examination, and 27 (18%) showed erythema 40 mm and larger. They were indicated chemoprophylaxis as they were most likely newly infected in this epidemic. After 2 months, a second contact examination was conducted for the students (excluding those who underwent chemoprophylaxis or had tuberculosis) and all teachers. Based on chest X-ray examination, two new students and one teacher were diagnosed as pulmonary tuberculosis, and another one student was diagnosed as tuberculous pleurisy. Comparing the erythema size distribution in the first and second tuberculin tests, the distribution of the latter markedly shifted to right, namely became much larger than the former. It was assumed that students in whom the difference in erythema diameter was larger than 17 mm between the first and second examinations had been newly infected in this epidemic. Chemoprophylaxis was indicated for 45 students and 3 teachers. After 6 months, a third contact examination was conducted for the students and teachers (excluding those who underwent chemoprophylaxis or had tuberculosis). After a year, one teacher was diagnosed as pulmonary tuberculosis by the fourth contact examination (chest X-ray). Restriction fragment length polymorphism (RFLP) analysis was carried out with 2 strains of M. tuberculosis isolated from these patients (the index case and the second teacher patient), and the RFLP pattern of 2 patients was same.