A survey was carried out among 12,535 children in the age group 0-9 years of 90 villages in Doddballapur sub-division of Bangalore district to study the possible variation in the prevalence of tuberculous infection among the unvaccinated children in a village depending upon the varying prevalence of BCG scars in the same population. In each village, all the children in the age group of 0-9 years were registered and examined for the presence or absence of the BCG scar. Of the 12,535 children, 6269 (50%) who did not have BCG scars were eligible for tuberculin test, while 6045 were actually tested. Each child without BCG scar was tuberculin tested with 1 TU RT 23 with tween 80 and the reaction read between 72 and 96 hours. Two proportions were calculated in each village viz., a) the proportion with BCG scars and b) that of infected children among those without scar and the villages were distributed by these two proportions.

On the basis of distribution of tuberculin reactions, 10 and 12 mm induration was the demarcation between positive and negative reactors. Prevalence of infection among 0-9 years was 4.9%, 2.6% among 0-4 years and 8.9% among 5-9 years. Distribution of villages according to two variables i.e., prevalence of BCG scars and prevalence of infection among unvaccinated children did not show any correlation with the prevalence of infection among the unvaccinated in the same villages.

It is seen from the study that exclusions of various proportions of children with BCG scars did not have any correlation with the prevalence of infection among the unvaccinated in the same villages.

In non-e of the villages any association was seen between these two. In view of this finding, it is felt that the simple method of periodic tuberculin testing of the population in younger age groups could be developed into a method of tuberculosis surveillance even in areas where direct mass BCG vaccination is given. This would appear to be the cheapest, practicable and technically appropriate method of studying the overall tuberculosis situation.