[Tuberculin tests in school leavers in canton Berne , Neuenburg and Wallis 1992/1993]

To determine the prevalence of tuberculosis infection in Switzerland, standardized tuberculin tests using 2 units of tuberculin Berna PPD RT 23, administered by specially trained personnel, were performed on school leavers in 3 Swiss cantons in 1992/1993. Of the 7036 school leavers, averaging 15 years of age, only 294 (4.18%) were not BCG-vaccinated. Non-vaccinated persons had tuberculin test indurations > 15 mm in 2.04% (6663 BCG vaccinated persons in 1.14%). Calculations of potentially influential factors using stepwise ordinal polychotomous regression showed that tuberculin test indurations are significantly larger after BCG vaccination, as well as with increasing age at immigration from high prevalence tuberculosis countries. Indurations were smaller with increasing time passed since BCG vaccination, as well as in females. Pets at home did not significantly influence the size of tuberculin reactions. Theoretically the positive predictive value of tuberculin tests in Switzerland is small because of the low tuberculosis prevalence. From our data the maximal prevalence of infection in 15-year-olds is estimated at 0.91% (2.48% in the non-vaccinated) in Swiss and 2.54% (9.77% in the non-vaccinated) in foreign born school children. These rates, higher than extrapolated from previous studies, are comparable to data from other industrialized countries. They do not warrant a change in BCG vaccination policy in Switzerland, which since 1987 requires BCG vaccination in children immigrating from countries with high tuberculosis prevalence only.