Determination of the prevalence of infection with Mycobacterium tuberculosis among persons vaccinated against Bacillus Calmette-Guerin in South Korea

The prevalence of tuberculous infection was estimated among 12,032 persons with a Bacillus Calmette-Guerin (BCG) vaccination scar and 7,788 persons without such a scar who participated in a nationwide tuberculin skin test survey conducted in the Republic of Korea in 1975. The analysis was built upon mixture models that captured the heterogeneity of indurations arising from tuberculous infection, cross-reactions due to infection with environmental mycobacteria, and BCG vaccination. The three distributions were allowed to vary by age, sex, and BCG vaccination status in the Bayesian manner, according to the prior opinion of the authors. Estimated prevalences of tuberculous infection were similar among persons with a BCG scar and persons without one: 7.5% (95% credibility interval (CI): 3.1, 12.5) and 5.2% (95% CI: 4.2, 6.3), respectively, at age 0-4 years and 87.3% (95% CI: 84.0, 90.2) and 84.0% (95% CI: 81.9, 85.8), respectively, at age 25-29 years. From this analysis it can be concluded that mixture models allow investigators, for the first time, to estimate the prevalence of tuberculous infection not only in unvaccinated persons but also in the BCG-vaccinated population. Mixture models are a versatile tool for analyzing diagnostic test data and more general classification problems of considerable complexity.