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 emp loyed during a 24-month period were included in the study. Employees were a dministered 2-step tuberculin testing, and BCG vaccination scars were verif ied. Results: Of 665 hospital employees studied, 239 (36%) had been vaccinated w ith BCG in childhood. Significant tuberculin reactions (greater than or equ al to5 mm) were more frequent among BCG-vaccinated (60%) than among nonvacc inated (29%) employees (odds ratio [OR], 3.6; 95% confidence interval [CI], 2.6-5.2). The predictive value of tuberculosis infection increased with in creasing reaction size and greater age (from 37% in subjects 30 years or yo unger with indurations greater than or equal to5 mm to 100% in subjects 50 years or older with indurations greater than or equal to 15 mm). Among 374 employees with a negative tuberculin test reaction who underwent a second t est, 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 BCC vaccination largely influences the tuberculin reacti on and the boosting phenomenon among hospital employees. The interpretation of the results of 2-step tuberculin testing in a BCG-vaccinated subject mu st take into account age, size of the reaction, and local prevalence of tub erculosis infection. No single criterion, however, can accurately separate reactions caused by true infection from those caused by BCG vaccination.