Material from a community survey carried out in rural areas of Karnataka by the National Tuberculosis Institute, Bangalore, has been analysed in an attempt to identify significant categories of the population that may yield higher proportion of cases. In all, 170 cases diagnosed among 61,581 persons have been distributed by their role, i.e., head of family (HOF) or not, kinship, (relationship to the HOF) by age and sex.

It has been observed that a comparatively small size of HOF male population (16.9%) would contain 55.9% of the total cases prevalent in the entire X-rayed population. On the other hand, the broad category other than HOF-male, would have case content relatively much less in proportion to their population size. Implications of the finding for house-to-house Case-finding by Multi-purpose Health Workers (HWs) are discussed here. It is possible to obtain higher case yield from the group having a higher case content which is aged 20 years and above and constitutes about 30% of the total population by confining to symptom screening. On the other hand, since cases are mostly in the HOF-males, would make it difficult for HWs to contact them in their normal visiting hours during day, as most of HOF-males may not be at home. Determined efforts have to be made by HWs to contact them during their beat schedule.

The National Tuberculosis Control Programme is in operation since 1962, and its quantitative achievement is being monitored indirectly through records and reports received from District Tuberculosis Centres. For direct evidence of impact of the programme, tuberculin surveys are useful in reflecting the recent epidemiological situations prevailing in the area. Tuberculosis being a disease of secular nature, a periodic follow up with five years (arbitrary) interval may be preferred over the continuous follow up, for finding the trend of tuberculosis situations in an area.

Keeping in view the importance of tuberculin surveys, National TB Institute (NTI) has evolved a surveillance system which can be adopted by any state in India. The state teams can be trained at NTI in registering population, tuberculin testing & reading, so as to carry out the surveillance in their respective areas. It is essential to create a central organisation for surveillance of tuberculosis using the tuberculin test. The centre would be responsible for technical & administrative support and monitoring. NTI could provide technical expertise in formulating the surveillance system, a training methodology and an in service training to the designated staff.

During a longitudinal survey, carried out in 119 randomly selected villages of Bangalore district for studying the time trend of tuberculosis, the average infectivity of a case over a period of one and a half years was found to be six. In 1986 i.e., 25 years after the start of I survey, 61 persons belonging to one village called Nunnur who were found newly infected between I & II surveys, were interviewed. Further, a general study of the layout of the houses and public facilities in the village was made. However, in Nunnur, there was just a single bacteriological case (index case) identified at the I survey. This index case was resident of household numbered 80 in the main village. This case study investigates the background of the observed high infectivity. The incidence rate of infection in Nunnur was 9.5% in 1½ years which is higher than the overall average rate of 4% as well as rate for 30 other single case villages i.e., 3.5%. The investigation reveals that at least 21 persons., found newly infected at II survey, had varying levels of contact with the index case. The remaining 40 infected persons could not be linked, either directly or indirectly, to any other known bacteriological case including the index case in the village. All the persons identified as infected at II survey were distributed throughout the village, beyond the likely zone of infection of the index case.

A study was conducted in 1983-84 by the National TB Institute (NTI) in the districts of Dharmapuri (Tamil Nadu) & Ananthapur (Andhra Pradesh). Thirteen health personnel were trained in census taking, tuberculin testing & reading and data keeping etc., at the NTI according to the standard methodology. The trainees were repeatedly assessed and only those who achieved a reasonably high inter-reader correlation with the standard reader were chosen for the field work. Field work was carried out by these health workers and supervised by the team leaders of NTI. Children between 0-9 years were tested with 1 TU RT 23 with Tween 80 in tuberculin testing centres specially set up in each village and the reactions were read between 48 & 72 hours after the test. The tuberculin testing/reading coverage was very high. Of 6702 eligible children, 5904 (97%) were tuberculin test read.

Individual reading assessment carried out at Ananthapur and Dharmapuri for the State Field Workers (SFWs) showed that agreement with Standard Reader (SR) of NTI at three induration levels i.e., 10+ mm, 14+ mm and 18+ mm were very high. The demarcation line between infected and uninfected appeared to be about 18 mm. In Ananthapur, the agreement at 18+ mm was 99% and at Dharmapuri it was 100% for SFW, and 98.4% for SFW-2. The estimates of prevalence rate of infection were 9.3% - SFW V/s 9.7% - SR at Anantapur, 5.2% - SFW V/s 5.2% - SR and 7.2% - SFW.2 V/s 7.2% - SR at Dharmapuri. The study further showed that it was possible to train general health workers, within a period of 3 months to attain a high level of efficiency. The general health services can successfully organise on their own a programme of tuberculin testing in the community with proper liaison and supervision by some nodal agency. The training and field supervision responsibilities may be shouldered initially by NTI or another suitable organisation, till these nodal agencies come up.

It has been postulated that BCG scar disappears in a good number of children and some of the vaccinated children will get included in the non- vaccinated group and cause difficulty in interpreting the results of tuberculin test. It was decided to analyse information on BCG scar status in the younger population of a rural community in 3 taluks of Bangalore district with an objective to find out whether disappearance of BCG scar is dependent on the age of the child, size of post-vaccination induration at initial survey and tuberculin sensitivity status of children in whom BCG scar has disappeared, in comparison with children in whom the BCG scar has not disappeared. In all, 1095 children aged 0 to 14 years were found with BCG scar in 119 randomly selected villages during an epidemiological survey done in 1961 at the time of intake. Following two groups of children were studied for disappearance of the scar. Of them, a) 796 children who had BCG scar at the first survey, and whose BCG scar status was available at 4th survey, b) 299 who showed no BCG scar at first survey but were found with BCG scar at 2nd survey and whose BCG scar status was available at 4th survey.

Of the BCG scars recorded at intake, 26.4% and 32.5% disappeared subsequently during three and a half and five year periods respectively. The waning of BCG scars was independent of age of the child and tuberculin sensitivity status at intake. Tuberculin sensitivity status in children in whom scar had disappeared was the same as that found in children in whom scar had persisted at intake and after five years. The misclassification of children, in whom scars have disappeared, as unvaccinated leads to a difficulty in interpreting the results of tuberculin test done for the purpose of computation of the Annual Risk of Infection. Further, the extent of misclassification increases in proportion with the increase in BCG coverage of the population. This finding justifies the practice of identifying the demarcation level on the basis of the distribution of tuberculin induration sizes for classifying the infected persons in a population in each survey.

Screening of the population by Mass Miniature Radiography (MMR) followed by sputum examination by culture of the X-ray abnormals is the customary method for arriving at the prevalence rate of cases in the community. It is not possible to use this methodology by states to carry out prevalence surveys in these areas, even if they desire to evaluate the effect of anti tuberculosis measures implemented by them. Therefore, simpler means of screening population through chest symptom for sputum examination has been studied by National Tuberculosis Institute (NTI). The objectives of the present investigation were to find out the prevalence of bacillary cases by screening the population through identification of chest symptomatics by Social Investigators (Sls) or General Health Workers (GHWs) compared to that by MMR. In a peri urban area 10 kms away and around Bangalore city all the villages were listed and of the 60 villages were selected on the basis of a sample random sample. Of them, 30 were covered by Sls of NTI and the other 30 by GHWs of the state government. The methodology adopted was that (1) After census taking and registration of the entire population aged 15 years and above, Sls questioned the persons house to house for presence of cardinal chest symptoms of any duration. All chest symptomatics were subjected to MMR and sputum examination. (2) Similar methodology was adopted by GHWs in the other 30 villages allotted to them. (3) Without knowing the symptom status of all the registered persons, aged 15 years and more belonging to all the 60 villages, were subjected to MMR and from among those having X-ray abnormalities, to sputum examination.

It was found that GHWs had identified the same proportion of the persons either having general symptoms or having chest symptoms from the general population, as Sls. Prevalence rates of culture positive as well as smear positive cases were similar by any of the three methods i.e., 0.18%, 0.23% & 0.25% respectively. Prevalence rates of smear positive cases obtained through symptom questioning, either by Sls or GHWs, were more or less similar to the estimates obtained by the more comprehensive screening method of MMR and/or symptom questioning. The culture positive prevalence rate following MMR screening was 0.25%, which was lower than the rates observed in other surveys. The paper discusses the possible hypothesis that could explain the observation. It also presents correction factors to compute rates comparable to the best estimate i.e., that obtained through comprehensive screening by MMR and/or symptom questioning, followed by sputum culture.

A study on awareness of symptoms of pulmonary tuberculosis and action taking was repeated in the 62 villages and 4 town blocks of Tumkur district of Karnataka after an interval of 12 years. In the earlier study, 2106 persons formed the study population. In the present study, 1752 were intaken to obtain a comparison of these 1752 intaken persons who were eligible for interview, 875 were X-ray positive and 877 X-ray normal (matched control).

The study showed that 95% of patients having radiologically active tuberculosis by both X-ray readers, 70% by one reader, 49.5% inactive by both readers, were aware of symptoms. According to the bacteriological status 79.5% had symptoms among those who were sputum positive by both microscopy and culture, 62.2% among those positive by culture alone and 73.7% among patients sputum positive by any method. Regarding action taking it was observed that 49.5% of the bacteriologically positive patients took some action compared by 70% of those found to have radiologically active disease by both X-ray readers. Thus action taking was higher among the latter category in both the studies. It may be due to the fact that extent of lesions are less advanced among those bacteriologically positive than among those who were in radiologically positive stage.

The findings of the study are similar to the earlier awareness study carried out in 1963 in the same area (Tumkur). This also indicates that in spite of having advantage of DTP for a decade actual and total benefits have not reached the people.