[An outbreak of Mycobacterium tuberculosis infection among young adults in close contact]

We experienced an outbreak of tuberculosis among young adults in close contact. The index case (case 1) was 22-year-old builder and was symptomatic for 9 months before diagnosis as pulmonary tuberculosis (PTB). His sputum smear was positive for tubercle bacilli. On immediate family contacts examination carried out at our hospital, his brother and sister (case 3, case 4) were detected as having PTB. His mother (case 5) and father (case 6) were later detected as having PTB by their symptomatic visits after some months, as tuberculin test as not done at first examination. Case 7 was 19-year-old-man, and was undiagnosed for 5 months. His sputum smear was positive. Immediately, contacts examination for case 7 as carried out at our hospital, and his colleague (case 8) was detected as having PTB. By interview with the case 7, it was found that the case 1 and the case 7 were close friends and spent long time together. Case 10 was 30-year-old builder, and he was accidentally referred to our hospital and was diagnosed as PTB. By the interview with the case 10, it was found that the case 1 and case 10 were members of builders group. This fact was informed to the F health center, and contacts examination for other members of the group were carried out by the F health center, and two young men were detected as having PTB. Analysis of restriction fragment length polymorphism (RFLP) showed that the case 1, the case 5, the case 7, and the case 10 were caused by the same strain of M. tuberculosis. Based on these findings, it is highly suspected that this outbreak was origined from the case 1, and 13 developed tuberculosis and 13 were primarily infected among contacts. The characteristics of this outbreak was that the family and contacts examination were enforced and most of the cases were detected at our hospital. If the outbreak of tuberculosis highly suspected, physicians should actively cooperate with health centers for contacts examination.