Correlation of tuberculin induration with the number of Bacillus Calmette-Guérin vaccines

In developing countries with a higher prevalence of tuberculous infection, usually more than one Bacillus Calmette-Guérin (BCG) vaccine is recommended. Revaccination can considerably alter the tuberculin skin test response and the diagnosis of tuberculous infection. In this study to assess the relationship between the number of BCG vaccinations and tuberculin skin reactions, 3548 children (ages 6 to 12 years) from 7 elementary schools were given 5 tuberculin units of purified protein derivative, and results were compared taking vaccination status into account. Forty-seven children were excluded from the study. Mean purified protein derivative induration size at 72 hours was 3.2 +/- 3.9 mm with no BCG scar (n = 1518), 6.3 +/- 7.8 mm with 1 scar (n = 1513), 10.7 +/- 6.2 mm with 2 scars (n = 433) and 14.8 +/- 4.3 mm with 3 scars (n = 37). In children with no scar the 90th percentile values of the size of the purified protein derivative induration were 10 mm. The 90th percentile values of children with one, two and three scars were 15, 17.5 and 20 mm, respectively. We suggest that tuberculin skin test responses be evaluated with regard to the number of previous BCG vaccinations.