Estimates of prevalence of non-specific tuberculin sensitivity in south Indian population are based on studies using large doses of tuberculin prepared from Mycobacterium tuberculosis. In the present study, comparison of tuberculin test done on 2168 children aged 0-9 years with 20 TU RT 23 and 5 TU Battey antigen, belonging to rural areas, have been done. The distribution of induration to 20 TU RT 23 test has been compared to that of 5 TU Battey test, to see whether estimates of prevalence of non- specific tuberculin sensitivity based on the former could be compared with those based on tests with antigen derived from other mycobacteria.

It was seen that distributions of reactions, mean size of indurations as well as percentages of positive reactors to either test were not significantly different in the two randomly selected groups i.e., one tested with Battey antigen and the other with 20 TU RT 23. The prevalence of non-specific sensitivity in 0-4 years age group based on Battey test was 18.4 per cent and that with 20 TU test, 16.6 per cent. In the age group 5-9 years corresponding rates were 54.2 and 60.1 per cent. From these observations, it is suggested that if other antigens are not available, 20 TU RT 23 could be used for estimation of non-specific sensitivity.

Out of 56,146 persons without BCG scar examined at the first survey in 119 villages of Bangalore district (1961-63), 22,468 were subsequently examined 3 times over a period of five years by tuberculin test, X-ray and sputum at intervals of 1½ years to 2 years. No organized anti-tuberculosis services were provided in the study area. On the basis of tuberculin status and chest X-ray interpretations, the population was classified into 6 sub groups for the study of risk of sputum positive disease viz., Normal X-ray (N), Inactive Tuberculosis (AB) & Probably Active Tuberculosis (CD) and each of these into tuberculin positives and negatives.

The annual incidence of sputum positive disease observed was 1.45 per thousand among 18,207 eligible persons aged 5 years and more. The incidence of the disease in tuberculin positive group was 7 times as compared to that among tuberculin negatives. The incidence rate of bacteriological disease was 0.79 per thousand among X-ray normals (N) of the first survey; it was 3.73 per thousand among persons with inactive tuberculous lesion and non- tuberculous shadows (AB) and 26.04 per thousand among the group of persons with active or probably tuberculous shadows (CD). Of the total incidence cases, 76% were contributed by the tuberculin positives. The group of active or probably active shadows (CD) contributed 26.6% of the total new cases. The population without any radiological abnormality (N) contributed 48.2% of the new cases.