Tuberculin Skin Test Distribution following a Change in BCG Vaccination Policy

Background: Epidemiologic data regarding tuberculin skin test (TST) responses are an important basis for TB control strategies. This study analyzed TST responses in Korea, which experienced a rapid change in BCG vaccination status. Methods: TST responses in young adults were examined over 5 years. Participants with active TB lesions were excluded. Results: A total of 5,552 participants were enrolled with median age of 21 years. When an induration diameter >= 10 mm was used as the criterion for a positive test, TST positivity fell (from 28.0% in 2005 to 15.3% in 2009); however, they remained steady when the criterion was >= 15-20 mm. A positive TST was associated with a personal or family of TB, the presence of a Bacille Calmette-Guerin (BCG) scar, and age (odds ratio [95% confidence interval] = 4.03 [2.61-6.22], 2.91 [1.80-4.71], 1.50 [1.31-1.72], and 1.15 [1.09-1.20], respectively). Among these factors, the decrease of participants with BCG scars was the most prominent change, which appeared to be associated with the change of TST positivity rate. Conclusion: Overall, the rate of TST positivity in Korea decreased. However, this trend seems associated with the change of BCG vaccination strategy rather than successful control of LTBI. This study showed that change in BCG vaccination strategy can have great impact on TB epidemiologic survey based on TST.