Specificity of tuberculin skin test improved by BCG immunization schedule change in Japan.

INTRODUCTION: Tuberculin skin test (TST) has been used to diagnose tuberculosis (TB) and latent tuberculosis infection (LTBI). However, in Bacillus Calmette-Guérin (BCG) vaccinated patients, TST tends to produce false-positive results. According to the previous vaccination schedule, Japanese people were mandated to receive up to three doses of BCG-vaccine. The vaccination schedule was changed in 2003 and as per the new schedule, only infants are administered a dose of BCG vaccine. Our hypothesis is that this change can lead to a reduction in the cross-reaction to TST. METHODS: We evaluated the TST results obtained from 1097 recruits from six defense camps and 667 recruits from an air base. These TST data were divided into two groups according to the date of birth: a new group and an old group according to the BCG immunization schedule. We then analyzed positive and negative reaction of TST and erythema sizes. RESULTS: We confirmed that the change in BCG-vaccination schedule significantly decreased TST false-positive reaction (Pmeta = 1.4 × 10-18; risk ratio = 0.83; 95% confidence interval: 0.80-0.87) and erythema size (Pmeta = 1.1 × 10-4; mean difference = 6.6 mm; 95% confidence interval: 3.2 mm-9.9 mm). CONCLUSIONS: We showed the reduction in BCG cross-reaction to TST, in the new BCG vaccination schedule group, compared to the old group, we also have extracted information on the improvement in the specificity of TST for LTBI and TB diagnosis, which resulted from BCG schedule change.