Tuberculosis outbreak among students in a boarding school.

Tuberculosis (TB) outbreaks present a public health challenge. Six cases of active TB emerged in a boarding school in Israel during 1 yr. An epidemiological outbreak investigation was performed, followed by implementation of control measures. The investigation included interviews, tuberculin skin test (TST) and chest radiographs of the students. Close contact (n = 155) was defined as being in the same class or dormitory with a patient. Remote contact (n = 246) was defined as being in the school. An epidemiological association was detected among five of the cases and a distinct pattern was found in molecular analysis. TST was performed in 398 (99.2%) students. Repeated (two-step) TST was applied to the close contacts. The degree of contact, country of origin and previous bacille Calmette-Guérin vaccination were significantly associated with TST reactions. Preventive directly observed therapy was completed by 157 (91.3%) students. During 5 yrs follow-up, no additional cases emerged. While investigating a tuberculosis outbreak, the definition of degree of contact is a significant predictor for detecting positive tuberculin test. Immigration from an endemic country, as well as previous bacille Calmette-Guérin vaccination have a major effect on tuberculin skin-test results. The directly observed therapy approach was found to be successful in preventing further morbidity.