[Screening of South Tyrolean school children after exposure to a tuberculosis case]

During a language course in Ireland 422 schoolchildren aged 15-17 years and 44 accompanying persons from the autonomous Province of Bolzano--South Tyrol in Italy were repeatedly exposed to a Mycobacterium tuberculosis complex culture-positive, but smear-negative Irish teacher for more than 10 lessons.

Immediate action included contact tracing of exposed persons, administration of a standardised questionnaire, intradermal PPD (5IU) testing and thorax X-ray of persons with an induration of > or = 5 mm in the PPD test. The questionnaire included information on demographic factors, symptoms, vaccination status, underlying diseases, regular medical treatment and past infection in the last three months. A control group of children with similar age and BCG vaccination status was enrolled in the same schools to estimate the effect of exposure and the influence of previous BCG vaccination and ambient non-tuberculous mycobacteria.

Exposure in Ireland was not associated with an elevated prevalence of positivity in the PPD test in the exposed group, but having intra-familiar contact with tuberculosis cases (OR = 3.3; 95 % confidence interval: 1.35-8.07) or being from school A (OR = 2.3; 95 % confidence interval: 1.19-4.32) was associated with an induration > or = 5 mm in the multivariate analysis.

Contact tracing is an important public health action after exposure to an infectious tuberculosis case, nevertheless, in this case it may have resulted in overtreatment of exposed persons. BCG vaccination may have a long-term effect on PPD skin testing.