During second epidemiological survey carried out in 1972-73, special efforts were made in 21 of 62 villages belonging to first survey (1961-62) to study the demographic changes and fate of TB cases after an interval of 12 years.

The findings were: The increase of dejure population was about 20% over a period of 12 years i.e., an annual increase of 1.7%. The age structure had altered mainly due to significant increase in the age group 60 years and above – 51% to 64% indicating aging of population. The loss of original population after 12 years was 44%, of which 33% was due to migration and 11% due to death. The overall migration was more among females. The migration rate was higher in younger age group, being highest in 10-19 years (49%), next in 0-9 years (38%). Thus, overall migration in 0-19 years was 43%. The death rate was highest in 60 years and above (58%). It varied from 4-9% in age group 0-39 years. Original population available after 12 years for re-examination was 56%. Distribution in different age groups were; 0-9yr = 57%, 10-19yrs = 47%, 20-49yrs = 66%, 50-59yrs = 44%, 60yrs and more = 28%.

Out of 88 X-ray suspect cases of earlier survey, 87 could be identified and present status of 72 were known. Of them, 16 were normal, 12 and 4 found to be suspect cases and bacillary cases respectively and 40 had died. Of the remaining fifteen, 11 migrated and 4 not examined. Out of 14 bacillary cases, 13 could be identified. Of them, 3 were sputum negatives (2 normal and 1 suspect case) 9 had died and 1 migrated.

In this study the material from “Five year study of Epidemiology of Tuberculosis” (1961-68) has been analysed to find out an improved method of interpretation of chest X-rays to get accurate estimation of prevalence of “suspects” in the community. The population of a random sample of 119 villages from the three taluks of Bangalore district was surveyed four times with intervals of 1½ to 2 years by tuberculin testing, 70mm chest photofluorography and sputum bacteriology. Out of 45,434 persons X-rayed during the first survey, 590 were read as active pulmonary tuberculosis on the basis of single picture interpretation by two independent readers. Of them, 460 being sputum culture negative were classified as initial “suspects” and these were reviewed in this study by the panel of three readers together by the method of “joint reading”. The interpretation was done comparing the serial X-rays of individuals taken at intervals along with other available examination results and personal data. Out of 460 initial suspects only 110 (23.9%) were confirmed as “suspects”, the remaining were judged as non-tuberculous and/or inactive tuberculous (62.2%) and normals (13.9%).

Fates on five year follow up were compared between 85 “confirmed suspects” and 385 “initial suspects”. The mortality and sputum positive status were found more among the former group i.e., 23.5 and 25.5 and 14% and 7.2% respectively. Radiologically, 48.7% of the confirmed suspects and only 10% of the initial suspects could be classified as suspects at 5th year follow up. Incidence of bacillary disease among the confirmed suspects was also found higher. On the basis of “joint reading” and five year follow up study, the limitations of single picture interpretation resulting in considerable over diagnosis were clearly seen. The comparative reading of serial X-rays along with other examination results did help in the better assessment of etiology and activity status of disease. Of the X-rays read as non-tuberculous and inactive tuberculous when reviewed by “joint reading” method, about 67 more suspects could be added. Even then the estimates of prevalence of “suspects” based on single film interpretation which are widely used in India appear to be about 3 times the actual prevalence.

This paper reports on a study conducted in the year 1975 to estimate yield of tuberculosis cases from multiple sputum specimens, and work out correction factors to be applied to estimates based on small number of specimens. Eight sputum specimens were collected within a fortnight from each person with an abnormal chest X-ray during an epidemiological survey in 77 villages in a district of south India. Each specimen was examined by Ziehl-Neelsen technique of microscopy and culture. In all, 3,199 persons were referred for sputum examination and results of all the eight specimens were available for 1,652. Of the latter, 64 were culture positive.

The first specimen detected 58% of the culture positives and the additional positives by later specimens generally decreased. The contribution from the first specimen was 71% for cultures showing good growth and 19% for cultures with scanty growth. Similarly for positives on both culture and microscopy, first specimen detected 87% whereas the corresponding proportion was 32% for those positive only on culture. The type of specimen (viz., spot or overnight) and age or sex of the case did not influence the yield from multiple examinations. The precision of an estimate of prevalence will depend on the number of specimens on which it is based and the coverage obtained in the collection and examination of specimens. Correction factors to be applied to such estimates based on one or two specimens, for various levels of coverage have been presented. For example, an estimate of prevalence based on one sputum specimen with 90% coverage will have to be nearly doubled to get a more precise estimate. Using these correction factors, revised estimates of prevalence have been presented for a number of prevalence surveys conducted in India. It has been estimated that the total number of infectious cases in India at present may be at least 3 million, as against 2 million according to earlier estimates.

A study was carried out mainly to find out the prevalence and incidence of sputum negative active pulmonary tuberculosis (suspect cases) among 35,876 persons aged 5 years and above in rural areas of Bangalore district during 1968-72. Two surveys (I & II) at an interval of 3 months, succeeded by a follow up examination of the X-ray abnormals of the earlier surveys, were conducted in the same villages. Examinations at each survey consisted of tuberculin test, X-ray and sputum examinations. X-rays were interpreted individually at the time of each survey by single picture interpretation method and subsequently by Joint Parallel Reading (JPR) method to arrive to a diagnosis. In the JPR method X-ray readings and their comparison was done by a panel of three X-ray readers with full knowledge of age, sex, result of sputum examination and tuberculin test of each person with chest abnormality at any of the three surveys.

On a single picture interpretation the overall prevalence rate of suspect disease was found to be 5.4 per thousand at I survey and 4.59 per thousand at II survey. There was no significant difference in the overall age and sex specific prevalence rates of suspect disease between I & II surveys. Incidence of suspect disease at the end of 3 months was 2.24 per thousand. By JPR method the prevalence rates of suspect disease was 3.2 per thousand at I survey and 3.6 per thousand at II survey. The prevalence rates by single picture method were overestimated to the extent of 38% at I survey and 19% at II survey when compared with those found by JPR method. At I survey prevalence rates on JPR method was significantly lower than by single picture method. This was not so at II survey. Similarly, incidence rate of 0.2 per thousand of suspect disease on JPR was about 1/10th of that found by single picture method.

The incidence of bacteriologically positive cases in 6 months from among suspect cases on JPR was found to be 28%. Majority (76%) of non-tuberculous or inactive tuberculous shadows continued to remain as such after 6 months and about a quarter (23%) became normal. Incidence of bacteriologically positive cases from this group was minimal. Of 19,640 persons with normal X-rays 134 (0.7%) developed new shadows in 3 months; 103 (0.5%) cleared after 2-12 weeks (fleeting shadows). Mis-interpretation of the latter as active tuberculous may falsely boost the estimates of suspect disease to the extent of about 5%.