The significance of positive Mantoux reactions in BCG-vaccinated children

As the interpretation of tuberculin skin tests is controversial in subjects who have received BCG vaccine, we administered Mantoux tests to 2588 randomly selected Saudi children aged 5–13,1945 of whom had been vaccinated with BCG at birth and 643 were unvaccinated. Only 7.8% of the BCG-vaccinated children were Mantoux positive (⩾10 mm induration) at the age of 5 years, which was not significantly different from the unvaccinated children.

The tuberculin sensitivity rose more steeply with age in the BCG-vaccinated than the unvaccinated children so that the difference between both groups became statistically significant in those aged 12 and 13 (20% versus 3.9%,15.5% versus 4.1 % respectively). These findings support the previously expressed theoretical postulates that BCG-vaccinated subjects display an increased ability to respond immunologically to encounters with environmental mycobacteria. In communities with low prevalence of environmental mycobacteria, this would result in a slow but persistent rise of skin reactivity to tuberculin which, if given time, will become greater than that of unvaccinated subjects.