Effect of number of BCG vaccination on tuberculin induration size

The aim of this study is to interpret purified protein derivative (PPD) induration sizes with respect to the number of Bacillus Calmette-Guérin (BCG) scars.

We have considered 1879 school children between the ages of 7 and 14 years from seven primary schools in Kocaeli, Turkey. Children were injected with 5TU 0.1 mL PPD and induration sizes were measured at 72 h. Number of BCG scars, PPD application dates and induration sizes were recorded for each pupil. This study was also evaluated further for 312 households.

The mean diameter of PPD induration size for 0, 1, 2 and 3 BCG vaccination scars were 1.43 mm (95% confidence interval (CI): 0.84-2.02), 6.39 mm (95% CI: 5.91-6.87), 10.46 mm (95% CI: 10.04-10.88) and 11.35 mm (95% CI: 9.36-13.34), respectively. Furthermore, 90% and 95% percentiles of PPD induration 0, 1, 2 and 3 vaccinations were 10 and 12 mm, 16 and 19 mm, 17 and 19 mm and 19.2 and 20 mm, respectively. There was evidence for a linear trend across from 0 to 3 BCG vaccinations, indicating that mean induration size increases with the number of vaccination scars. The size of indurations directly correlated with the number of vaccination scars, PPD induration size of children with no vaccination scar was quite small and it was generally less than 5 mm.

This study shows the importance of the number of BCG scars in the determination of PPD induration size limit when tuberculosis infection is evaluated.