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.

In a five year epidemiological survey conducted by National Tuberculosis Institute (NTI) from 1961 to 1968, the population was mainly classified into three epidemiological groups (i) with no radiological abnormalities seen in the lungs (Group N) (ii) having X-ray shadows of non-tuberculous etiology or tuberculosis etiology but judged as inactive (Group M) and (iii) with shadows of tuberculosis etiology judged possibly or definitely active but negative on culture (Group S). The objective of this paper is to compare the characteristics of cases coming from the above three groups (N, M and S) in respect to bacillary disease status (a) at the time of diagnosis and (b) after a lapse of time (Fate). Out of the total 172 new cases diagnosed during three follow ups, 70 were diagnosed between I & II surveys, 40 between II and III and 62 between III-IV surveys. In the two 18 months follow up periods, 45 of the total new cases had come from Group N, 31 cases from Group M and 34 cases from Group S, corresponding figures for 24 months follow up (III & IV surveys) were 26, 26 and 10 respectively.

In the 18 months follow up it was observed that proportion of new cases positive on culture in the three groups were not significantly different. Comparison of fate of cases coming from three groups were similar in terms of cure, death and culture positivity. The findings point out clearly that not only development of disease but also the fate of cases is independent of pre diagnosis status of the new cases.

From all the 3 groups, disease developed more rapidly in some cases than in others. This reveals that tuberculosis cases are not an uniform entity from the point of view of development of the disease and cure.