The effect of BCG vaccination on tuberculin reactivity and the booster effect among hospital employees.

BACKGROUND We estimated the effect of remote BCG vaccination on tuberculin reactivity and the booster effect among hospital employees. METHODS Cross-sectional survey at a university hospital. All personnel employed during a 24-month period were included in the study. Employees were administered 2-step tuberculin testing, and BCG vaccination scars were verified. RESULTS Of 665 hospital employees studied, 239 (36%) had been vaccinated with BCG in childhood. Significant tuberculin reactions (> or =5 mm) were more frequent among BCG-vaccinated (60%) than among nonvaccinated (29%) employees (odds ratio [OR], 3.6; 95% confidence interval [CI], 2.6-5.2). The predictive value of tuberculosis infection increased with increasing reaction size and greater age (from 37% in subjects 30 years or younger with indurations > or =5 mm to 100% in subjects 50 years or older with indurations > or =15 mm). Among 374 employees with a negative tuberculin test reaction who underwent a second test, 39 (43%) of 91 vaccinated subjects had a positive booster reaction in contrast to 51 (22%) of 232 nonvaccinated subjects (OR, 3.4; 95% CI, 2-5.7). Neither different size criteria nor different definitions of the booster effect had an impact on the predictive value of tuberculosis infection. CONCLUSIONS Remote BCG vaccination largely influences the tuberculin reaction and the boosting phenomenon among hospital employees. The interpretation of the results of 2-step tuberculin testing in a BCG-vaccinated subject must take into account age, size of the reaction, and local prevalence of tuberculosis infection. No single criterion, however, can accurately separate reactions caused by true infection from those caused by BCG vaccination.