An evaluation of the results of Mantoux test in children received BCG vaccine during the neonatal period

BCG vaccination has an important role in preventing the serious forms of tuberculosis in children. Adverse effects of BCG vaccination are uncommon in immunocompetent children. One of the side effects of BCG vaccine is its potential for producing hypersensitivity to tuberculin and difficulties in interpretation of PPD test results. Knowledge of the normal variations in the induration of Mantoux (PPD) test with age is of utmost importance in the interpretation of this test. Since no comprehensive study has been performed on this subject in our country, we undertook this investigation on 247 children with ages from three months to 8 years who had been admitted to pediatric ward of Kerman university hospital No.1 and in whom all confounding variables had been omitted. Of all children hospitalized in our pediatric wards, those cases entered this study who were three months to 8 years of age and who had received BCG vaccine in the neonatal period. The result of PPD test was negative (Induration of 0-4 mm) in 78 cases (31.6%), doubtful (5-9 mm) in 138 cases (55.9%), and positive in 31 cases (12.6%). There was no statistically significant correlation between the degree of induration in the PPD test and age of the children (r=0.0262; P=0.341). However, when the study group was divided into two age groups of below one year and above one year of age, we found two different trends; in the former age group the amount of induration decreased significantly with age (r=-0.2857; P=0.002), while in the latter group induration increased significantly with age increase (r=0.1812; P=0.014). This investigation demonstrated that in the first few months of life and in the period after 24 months of age, there is a higher probability for finding positive results (?10mm). We can attribute these results to the effect of vaccination-in infants younger than six months of age and environmental factors such as increased contact of children with atypical Mycobacteria for children above 24 months of age, though it is necessary to investigate these cases for the presence of tuberculosis. In infants from 6 to 36 months of age, who have the highest rate of negative results, a more cautious approach must be taken in case of the PPD induration diameter of 10 mm or above.