TUBERCULIN TEST IN SCHOOL LEAVERS IN CANT ONS-BERNE, NEUCHATEL AND VALAIS, 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 sc hool leavers in 3 Swiss cantons in 1992/1993. Of the 7036 school leave rs, averaging 15 years of age, only 294 (4.18%) were not BCG-vaccinate d. Non-vaccinated persons had tuberculin test indurations >15 mm in 2. 04% (6663 BCG vaccinated persons in 1.14%). Calculations of potentiall y 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 h igh prevalence tuberculosis countries. Indurations were smaller with i ncreasing time passed since BCG vaccination, as well as in females. Pe ts at home did not significantly influence the size of tuberculin reac tions. Theoretically the positive predictive value of tuberculin tests in Switzerland is small because of the low tuberculosis prevalence. F rom our data the maximal prevalence of infection in 15-year-olds is es timated 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 dat a 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 tuberculo sis prevalence only.