The purpose of this study was to find out whether the prevalence of infection in young children might be used as an index of the tuberculosis problem in a population. Tuberculin testing was done in a random sample of 2,883 children (0-4 years) in Bangalore city, of those 2,589 (89.8%) actually completed testing. A total of 4340 children were registered in 59 villages and of these 4090 (94.2%) were tuberculin tested. The villages were from Bangalore, Kolar and Mandya as these districts were within 100 miles from Bangalore city. The team went from house to house and made a complete registration of the children 0-4 years in the selected houses. Information on socio-economic status, density of population etc., was also collected before giving tuberculin 1 TU RT 23 with Tween 80.

The results of the study showed that prevalence of infection in 0-4 years age group of cantonment area was 1.6% and in the crowded city area 4.1% at 14mm induration level. In the rural population, the prevalence of tuberculosis infection was 2%. In the city, a positive correlation between tuberculosis infection and socio-economic condition was obtained while it was not seen in rural areas. It was not possible to establish any correlation between tuberculosis disease and infection either in rural or urban areas, as the population was not examined for the prevalence of tuberculosis disease.

The aim of modern Public Health Programmes, is a reduction in the total amount of disease in the community. The unit for treatment and cure is not an individual but a sick community. With this new aim, it becomes essential to know the size and extent of tuberculosis in the community as it will be helpful not for purposes of planning only but essentially for the assessment of their effect on the problem. An attempt is made to review the important features of the available knowledge about infection, morbidity and mortality through various surveys. (i) Prevalence of Infection: Tuberculosis infection is widespread in both urban and rural areas of almost all parts of the country. Nearly 40% of the population are infected. To avoid the effect of non- specific allergy and get a more reliable demarcation, tuberculin reactions of 14mm and more were considered as positive by National Tuberculosis Institute. (ii) Prevalence of morbidity: The prevalence of radiologically active tuberculosis in the population is likely to be 1.5%, Prevalence of bacteriologically confirmed diseases is 0.4%. Based on single sample of sputum examination, the prevalence of infectious cases in the country is probably an under estimate. About two million are infectious at any one point of time. (iii) Mortality: Deaths from tuberculosis in the country is not definitely known. The impression of clinicians that death due to tuberculosis have fallen sharply may not be true. Half a million deaths will appear an underestimate. About 250 per 1,00,000 persons i.e., one million deaths due to tuberculosis per year seems to be a reasonable estimate. (iv) Bovine Tuberculosis: Only a few cases in man caused by the bovine tubercle bacillus have been reported although 2.75% to 25% of cattle have been found tuberculin reactors.

To put in a nut shell, the problem of tuberculosis in India is a gigantic one and our means of fighting it with the single tool of BCG, do not even touch the fringe of the problem.

The objective was to establish the prevalence rates for tuberculosis infection, radiologically active pulmonary tuberculosis and bacteriologically confirmed diseases for different age and sex groups. Tumkur District in Mysore State consisting of 2,392 villages, 10 towns of was selected for the study. The district headquarter town Tumkur was excluded from the survey. Random sample of 62 villages and 4 town blocks having a population of 34,746 persons constituted the study population. All the individuals available in the registered population were given a Mantoux test with 1 TU RT 23 with Tween 80. Longitudinal diameter of induration was read 3-4 days after the test. At the time of tuberculin test, all persons aged 10 years and above were offered a single 70mm photofluorogram. For each picture read as abnormal, a spot specimen of sputum of the individual concerned was collected at the time of reading the tuberculin test. Age and sex distribution of infection and disease were studied.

Various parameters concerning the prevalence of infection and disease in the community were reported. Prevalence rate of infection in all ages and both sexes of the population was found to be 38.3%, radiologically active tuberculosis 1.86% and 0.41% sputum positive disease. The infection and disease increased with age; of the total diseased, half were in age group 40 years and more and about 2/3 among males.

The incidence of infection with mycobacterium tuberculosis is an index of the risk of infection to which a community is exposed. An accurate estimation of incidence rate is of considerable importance in understanding the epidemiology of tuberculosis in organising control measures. A new method of estimating incidence of infection is discussed. The material from 3 studies of National TB Institute has been utilized. Study I: is a part of a survey of a random sample of 134 villages. No previous tuberculin testing or BCG vaccination had been carried out in the area, but each person was examined for BCG scar in order to exclude persons vaccinated probably from other areas. After a complete census, a Mantoux test with 1 TU of PPD RT 23 with Tween 80 given on two occasions (Round I and II). Those with reaction of 13mm or less at Round I were offered a test with 20 TU with Tween 80 within a week of 1 TU test. The interval between the rounds was about 18 months. From the analysis of the data from the first 50 villages for which complete information for both rounds was available, it was seen that there was a general increase in the size of reactions elicited in the second round. Study 2: tuberculin testing was carried out with 1 TU and 20 TU among selected ‘control’ groups which provided the data regarding the “enhancing of tuberculin allergy” seen in repeat tuberculin tests. Study 3: in the course of the longitudinal “survey reader assessments” were carried out periodically to judge the standards of the tuberculin test readers. Inter & intra-reader comparisons were made. The findings have been used to estimate the magnitude of reader variation. The data was also used to study variations in the technique of testing and reading.

It was estimated that on an average inter & intra-reader variations between the rounds were unlikely to exceed 6mm or more in more than 5% of the observations. The reading errors have an equal chance of being positive or negative except at extreme ends of the distribution where zero readings of Round I can only show an increase, and the very large reactions had a greater chance of showing only a decrease at a subsequent round. The study mainly concerns with the problems of estimating the incidence of tuberculous infection in a community. Calculations based on age-specific prevalence rates or on rates of tuberculin conversion or both subject to gross error, leading to unreliable epidemiological conclusions. For estimating the newly infected, a new approach has been suggested based on the drawing of a curve for the distribution of differences in reaction size from one round of tuberculin testing to another. It is assumed that if new infection causes a distinct rise in the degree of tuberculin sensitivity which is greater than the combined rise due to enhancement and reader variation, the distribution of differences between the rounds should indicate the newly infected. It is shown that the newly infected probably constitute a homogeneous group with an increase in mean reaction size of about 24mm and standard deviation of 4mm. Accordingly, 98% of the newly infected show an increase in reaction size of 16mm or more.

Studies on the distribution of tuberculous infection and disease in households have mostly been restricted to the examination of contacts of known cases. Clinical experience has lead to a strong belief that tuberculosis is a family disease and contact examination is a “must” for case-finding programmes. A representative picture of the distribution of infection and disease in households can be obtained only from a tuberculosis prevalence survey.

This paper reports an investigation, based on a prevalence survey in a rural community in south India. The survey techniques and study population have been described in an earlier report. Briefly, the defacto population was given a tuberculin test with 1 TU of PPD RT 23 with Tween 80 and those aged 10 years and above were examined by 70mm photofluorography. All the X-ray pictures were read by two independent readers. Those with any abnormal shadows by either of the two readers were eligible for examination of a single spot specimen of sputum by direct smear and culture. The defacto population numbered 29,813 and tuberculin test results were available for 27,115. After excluding BCG scars, the study population of 24,474 was distributed over 5,266 households which were further classified as “bacillary case household” with atleast one bacteriologically confirmed case, “X-ray case household” with atleast one radiologically active case but with no bacillary cases and ‘non-case household’ with neither a bacillary nor an X-ray case. Total bacillary cases were 77 and were distributed in 75 household. 74 households had one case each and one household had 3 bacillary cases.

The findings of the study have thrown considerable doubt on the usefulness of contact examination in tuberculosis control; (1) over 80% of the total number of infected persons, in any age group, occurred in households without cases, (2) cases of tuberculosis occurred mostly singly in households, and the chance of finding an additional case by contact examination in the same household is extremely small, (3) a common belief has been that prevalence of infection in children in 0-4 age group is a good index of disease in households, but in this study about 32% of households with cases of tuberculosis had no children in this age group, (4) in houses with bacteriologically confirmed case only 12% of the children in 0-4 age group showed evidence of infection, a possible explanation of such a low intensity of infection could be that there is resistance to infection. It is well known that some children even after repeated BCG vaccination do not become tuberculin positive. It is felt that a large number of children do inhale tubercle bacilli, but a primary complex does not develop or even if it develops, the children remain tuberculin negative. A hypothesis has been made that in addition to resistance to infection, there is something known as “resistance to disease”. Otherwise, it is difficult to explain why under conditions of heavy exposure in infection, only some individuals develop evidence of infection and very few develop disease thereafter.

The prevalence and incidence rates of tuberculous infection and disease in the community are known in the age group 10 years and above from several surveys carried out so far. The present paper provides various parameters of tuberculosis in particular in the pediatric age group. A random sample of 119 villages in 3 taluks of Bangalore district were surveyed 4 times from May 1961 to July 1968 at intervals of 18 months, 3 years and 5 years of the initial survey. Tuberculin test was done for the entire available population with 1 TU PPD RT 23 with Tween 80, and 70mm X-ray for all available persons aged 5 years and above. Two samples of sputum were obtained from the X-ray abnormals, and examined by smear and culture.

It was found that prevalence of infection increased with age from 2.1% at 0-4 year age group to 16.5% at 10-14 year age group, compared to 47% at 15 years and above age group. Prevalence of disease in 5-14 year age group was considerably lower than in age group 15 years or more. Tuberculosis morbidity increased with the size of tuberculin reaction and it was high among children with reaction 20mm or more. Incidence of infection increased with age from 0.9% per year in age group 0-4 years to 2.8% per year among that of 15 years and above. Incidence of disease also showed the same phenomenon-, rising from 0.5% in age group 5-9 to 4% per year in the age group 15 years and above. There were 10 sputum positive cases in 5-14 years of age in first survey, of them, 8 became negative and one died. While from among 152 cases in 15 years and above age group, 48 became negative, 72 died and 32 remained positive. The fate of cases of pulmonary tuberculosis in 5-14 years age was not as serious as in 15 years and above age group. The survey had no means of examining miliary and meningeal tuberculosis.

Children as well as adults with larger reaction of 20mm or more to tuberculin test had higher mortality. This could be considered due to tuberculous infection after taking into account death due to non- tuberculous reasons in both the infected and uninfected groups. Use of chemoprophylaxis might be considered for those who give history of contact with open cases and have tuberculin reaction size 20mm or more.

Data from 62 randomly selected villages in a district of south India, which formed part of a prevalence survey carried out by the National Tuberculosis Institute, Bangalore, during 1960-61, has been made use of. The survey covered 29,813 persons in 5,266 households. There were 70 cases with bacilli demonstrable either in smear or culture and 300 suspect cases. Using the village map (prepared by survey staff), ‘case clusters’ were formed first, with each case household as nucleus and adjacent households within a maximum distance of about 20 meters on either side of the case households. Households closest to the nucleus household on either side have been called as 1st neighbourhood and those coming next in proximity on either side as a 2nd neighbourhood and so on. The case household and its four neighbourhood together was called a cluster. If another case household was found within 4th neighbourhood of the first case the cluster was extended by including the 4th neighbourhood of the new case also. Such clusters were called composite case clusters and clusters with only one case household as simple case clusters. Similarly, suspect case clusters were formed and differentiated as simple suspect clusters or composite suspect clusters. Further, to serve as a control group, non-case clusters were constituted from a systematic sample of 10% households that were not included in case or suspect case clusters.

Out of 60 case clusters formed, only 7 have multiple cases showing that there was no evidence of high concentration of disease in case clusters. While the percentage of child contacts (0-14 years) infected was considerably higher in case clusters (25.8%), there was not much difference between suspect case clusters (14.9%) and non-case clusters (9.8%). Similarly, there was not much difference between simple and composite clusters. Infection among child contacts was higher in case households as compared to their neighbourhoods. To get some idea of the zone of influence of a case or suspect case, prevalence of infection was studied for 10 neighbourhoods, in simple clusters to avoid the influence of multiple cases. It appeared that the zone of influence of a case may extend at least upto the 10th neighbourhood. It was also noted that there was very little difference between zones of influence of suspect cases and non-cases. Case clusters in which the nucleus case had shown activity of lung lesion (evident on X-ray reading) or had cough showed significantly higher infection among child contacts. Clusters around cases positive on both smear and culture did not show higher infection than those around cases positive on culture only. (This may be due to sputum examination of single specimen only).

Out of the total infected persons in the community, only 2% were in case households and 7% in suspect case households, over 90% being in non-case households. The zone of influence of a case extending at least upto the 10th neighbourhood and the overlapping of such zones of influence of cases, present and past, seems to be the most probable explanation for the wide scatter of infection in the community. Prevalence of infection among child contacts was definitely higher in case clusters. But, the significance of this could be understood only from a study of the incidence of disease during subsequent years in different types of clusters. It is significant that only 10% of the total infected persons in the community were found in case clusters. The case yield in general population, cluster contacts, household contacts and symptomatics attending general health institutions have been also compared. The case yield in the last group (10%) is much higher than the case yield from both types of contacts (0.7% and 0.6%) which where only slightly higher than the case yield from the general population (0.4%).

A rural population of 65,000 belonging to 119 randomly selected villages of Bangalore district was repeatedly examined four times during 1961 to 1968, by tuberculin test, X-ray and sputum examinations, to study the epidemiology of tuberculosis without any active anti-tuberculosis measures. The interval between the first and the fourth examination was 5 years. The coverage of various examinations at different surveys were very high.

The main findings of the study are: Prevalence rate of tuberculous infection in the population was about 30% (among females 25% and males 35%). The overall prevalence rates of infection were fairly constant at all the four surveys, but a steady decrease in the prevalence of infection was observed in the age group 0-24 years. Annual incidence rate of infection on the average was about 1%. During the study period, the incidence of infection showed a decline from 1.63% to 0.8% for all ages combined. Prevalence rate of disease ranged from 337 to 406 per 1,00,000 population during the study period, the highest being at the time of first survey and lowest at the time of third survey. For the younger age group of 5-34 years, the rates showed continuous decrease during the study period. Annual incidence rate of disease ranged from 79 to 132 per 1,00,000 population, highest being between first and second surveys and lowest between second and third surveys. The incidence rate in younger age groups below 35 years showed a decline during the study period. Those with tuberculin test induration of 20mm or more had highest annual incidence rate of disease. The annual incidence rate of bacteriologically confirmed disease in the three radiological groups of population was (i) 185 per 1,00,000 with normal X-rays, (ii) 958 per 1,00,000 with abnormal shadows judged as inactive tuberculous are non-tuberculous and (iii) 4,530 per 1,00,000 with abnormal shadows judged as active or probably active tuberculous but bacteriologically not confirmed. The third group constituted 1% of the total population and contributed 34% of the total incidence cases. In each of the above three radiological groups, the incidence of disease was highest among those with tuberculin test induration of 20mm or more to 1 TU RT 23 with Tween 80. Those with 20mm or more tuberculin test induration in the third radiological group constituted 0.45% of the total population but contributed 27% of the total incidence cases. Incidence rate for males was nearly double that of females. More than half of the new male cases were 35 years of age, whereas more than half the females were below the age of 35 years. Out of 126 cases followed up at three subsequent surveys over a period of 5 years, 49.2% died, 32.5% got cured and 18.3% continued to remain sputum positive. Both death and cure rates were highest during the first one and a half year period.

About 30% of newly detected cases come from population uninfected at an earlier survey. Both infection and disease showed a decline in the younger age group. There was no evidence of an increase in drug resistance among newly diagnosed cases. Incidence of cases showed a higher natural cure. These findings indicate that tuberculosis cases are not a uniform entity. There can be different gradations from the point of view of diagnosis and ability to benefit from treatment. The differences between male and female patients with regard to death and cure rates support this view

Some of the parameters relating to duration of infected status and incidence of disease have been measured by analysing the data collected from the five year study. Between 1961-68, 119 villages in Bangalore district with total average population of about 62,000 were surveyed at intervals of 1, 3 and 5 years from the first survey. All persons were tuberculin tested with 1 TU RT 23 and those aged 5 years or more were X-rayed. Sputum of those persons showing any X-ray abnormality were collected and examined for AFB. Persons with X-ray abnormality but bacteriologically negative or with normal X-ray in all the preceding surveys, and who became culture positive with X-ray abnormality in the current survey were termed as "New cases". New cases who had shown 10 mm or more reaction to 1 TU RT 23 at I Survey were considered infected previously. New cases, tuberculin negative at I survey but who showed an increase of 16 mm or more between two consecutive surveys were considered infected midway between the two surveys.

Of the 42 new cases diagnosed from among the newly infected during 5 years, 81% came from those infected within one year. Incidence rate of cases among those who were infected within one year was about 5 times more than those infected earlier than one year. Incidence of cases steadily decreased with the increase in the duration of infection. Further, it was found that one fourth of all newly diagnosed cases came from the newly infected persons. However, the size of the pool of previously infected persons in a community being much larger, at least 72% of the new cases came from the reservoir of previously infected persons. The incidence of disease among the newly infected was almost the same in the three age groups i.e., 5-14, 15-34 and 35 years or more. But, the ratio of the incidence rates for the newly infected and the previously infected decreased from 13 for the age group 5-14 to 3 for the age group 35 years and above. In other words, the incidence of disease among the newly infected in the age group 5-14 was thirteen times more than for the previously infected in the same age-group whereas in the age-group 35 years and above, the incidence among newly infected was only thrice that among the previously infected.
Out of the 160 new cases diagnosed during the three repeat surveys, 21 per cent cases came from among those who were infected on the average for one year or less. This is almost in conformity with the hypothesis that one-fourth of all new active cases come from new infections less than a year old.

The data from a tuberculosis prevalence survey carried out in three taluks of Bangalore district in south India during 1961-68 were analysed to study (i) the prevalence of non-specific sensitivity in the community i.e., prevalence of infection with mycobacteria other than M.tuberculosis, as found by testing the population with tuberculin RT 23 of a lower strength (1 TU) and higher strength (20 TU), both with Tween 80 and (ii) additional boosting if any, resulting from testing with higher dose of tuberculin, immediately following a test with 1 TU RT 23.

The level of demarcation between infected and uninfected with 1 TU was 0-9 mm induration size and this negative group tested with 20 TU dose induration of 8 mm or more was considered positive. Prevalence of infection with M.tuberculosis in the community were 2.1% in 0-4 years, 7.9% in 5-9 years, 16.5% in 10-14 years, 33.2% in 15-24 years and overall 14.5% in 0-24 years of age group. Infection rate with other mycobacteria were 12.9%, 44.9%, 66.2%, 62.4% and 45.7% respectively in the above stated different age groups.

Testing the population with 20 TU RT 23 following a 1 TU test was found not to boost the tuberculin reactions over that observed on a single test with 1 TU only.

A study was conducted in a slum area of Bangalore, to get information on the prevalence of all forms of tuberculosis in 0-4 year age group, respiratory tuberculosis in 5-14 year age group and the proportion of respiratory tuberculosis among total respiratory diseases in 0-14 year age group. Entire population in a slum area was investigated. Children aged 0-9 years were given tuberculin test and their nutritional status assessed. All persons were X-rayed. Sputum specimens were collected from those having radiological abnormality in chest, chest symptoms of one week or more in 0-4 years, in addition from those with any kind of sickness, malnutrition and tuberculin reactors.

In 0-9 year age group, 5.5% were tuberculin positive (without BCG lesions), in 0-4 years, 1.8% and 5-9 years, 11.3%. Among the X-rayed children, 47.4% had some kind of sickness, the proportion being significantly high in 0-4 year age group. The respiratory sickness is the commonest among children of all ages followed by malnutrition (21%). Among children with chest symptoms, upper respiratory infections were 33%. Chest X-ray abnormalities were present in 4.5% of children and of these 82.5% had non-specific pneumonitis. Of 71 persons with respiratory disease, about 7% were tuberculous. Out of 1408 children, only 5 had active primary tuberculosis, giving a prevalence of 0.35%. None in 0-4 year age had sputum positive disease or extra pulmonary tuberculosis.

It has been highlighted that non-tuberculous chest diseases are common in pediatric age group and many of these may be wrongly classified as active tuberculous in practice. It is concluded that tuberculosis in the pediatric age group in this community is not a serious public health problem.

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.

Prevalence of tuberculous infection in young children is an important surveillance measure. However, the hypersensitivity may be depressed by malnutrition and thus interfere with the interpretation of tuberculin test leading to underestimation of the infection rate. Objective of this investigation was to study the relationship between tuberculin reaction with 1 TU RT 23 and nutritional status of children. The study was carried out in 1974 among children aged 1-9 years of age living in an urban slum area of Bangalore city and who were not given BCG vaccination.

Of the 1151 registered children aged 0-9 years, 482 in the age group 1-4 and 526 in 5-9 years formed the study group. Of these 1008 children, 980 had both clinical evaluation and anthropometric measurement for nutritional status and 963 had both tuberculin test readings and anthropometric measurements carried out for them. Of the 482 children aged 1-4 years, 230 were classified as suffering from Protein Calorie Malnutrition (PCM) and of the 498 in the 5-9 years of age, 227 were classified as suffering from PCM. Distribution of tuberculin test indurations in mm among the normals and the undernourished were compared; no significant difference in the mean size of tuberculin indurations as well as in the distributions of these indurations was observed, regardless of the method used for arriving at the classification.

The trend of tuberculosis in a sample of 22 villages of Bangalore district observed over a period of about 16 years (1961-77) is reported. Distribution of tuberculin indurations did not show a clear cut demarcation between infected and non-infected. The method adopted to demarcate the cut off point has been described herewith: Distribution of tuberculin induration size of 0-14 years was attempted and extrapolated to higher age groups. Even in these younger age groups the antimodes were not clearly defined, so the antimode was arrived by fitting two normal curves as two likely modes.

The choice of demarcation level, therefore, is somewhat arbitrarily made on the basis of the distributions and these varied from survey to survey; between 10 mm at survey I and 16 mm at survey V. The actual and standardized infection rates showed more or less declining trend in 0-4 years, 5-9 years and 10-14 years age groups. The prevalence of cases was not significantly different from survey to survey (varying from 3.96 to 4.92 per thousand from first to fifth survey). However, there was a shift in the mean age of cases, and better survival rate of cases diagnosed at later surveys.

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.

To obtain precise information for computing the indices of tuberculosis situation in a community, with passage of time, reliance has been placed on tuberculosis infection rates obtained by carrying out tuberculin surveys. In most developing countries, covered extensively by BCG vaccination without prior tuberculin testing, the tuberculin test has problems of interpretation for demarcating the infected persons from the uninfected. To overcome the problem, therefore, the test results are analysed among persons who do not show a BCG scar and are, thus, considered as normal population. In this paper, an attempt is made to show that BCG vaccination not always lead to the formation of a scar, and also that the scar resulting from BCG vaccination may fade away with time and the person, thus, may be wrongly included in the unvaccinated group. It has also been found that there is greater fading of scars in the younger age groups: in children 0-2 years of age, upto 52% of the scars faded away within 21 months of vaccination. This proportion steadily decreased to about 8% in the 10-14 years age group.
The implication of the finding is that the demarcation line between uninfected and infected persons may require to be shifted from survey to survey, based on the distributions among the 'no scar' population. Moreover, in a totally vaccinated community, the differences of reactions may provide the answer to the problem of identifying the newly infected persons.

After the introduction of direct BCG vaccination, assessment of post-vaccination allergy and information about prevalence of infection could not be obtained. Few methods were tested i.e., i) retesting of persons with 0-13 mm reaction at site of vaccination on 4th day of vaccination, ii) retesting of all vaccinated persons of age 0-10 years. It is not only necessary to find out the size of BCG lesion that could separate them but also the day after vaccination on which the tuberculin reaction size best correlates with the BCG vaccination size. With this in view, two studies with regard to direct BCG vaccination done in India have been examined further. In Study I, 816 eligible persons were tested with 1 TU RT 23 read on 3rd day and vaccinated with either Indian or Danish vaccine. The vaccination lesions were examined on the 3rd, 6th and 90th day of vaccination. On the 90th day post-vaccination tuberculin test was done and read on 3rd day. In Study II, a total of 691 who had no previous BCG scar were simultaneously tuberculin tested with 1 TU RT 23 and vaccinated with either Indian or Danish vaccine. The BCG lesions were examined every day and on 39th and 90th day.

The correlation of pre-vaccination tuberculin test and BCG lesion size showe d that sixth day in first study and fifth day in second study was the highest. Tuberculin reaction size of 10 mm or more correlated well with 14 mm or more induration size of BCG in classifying the persons as infected and non-infected. Correlation between the size of BCG scar at 3 months and size of pre-vaccination tuberculin reaction was poor. Considering the two studies together vaccination induration of 14 mm or more on 5th or 6th day appears to be the best criterion for demarcating the infected from non-infected. Some other choices are 12 or 14 mm levels on 2nd day, 10 and 12 mm levels on 5th day and 10 mm levels on 8th day seems to be nearly as good and operationally useful.

A BCG Vaccination induration size of 14 mm and above between 5th and 6th day of vaccination, for all practical purposes may be considered satisfactory for demarcating persons infected with M.tuberculosis from those non-infected. It can be concluded that estimation of prevalence of infection, when BCG vaccination is given to all without prior tuberculin testing, can be made on the basis of BCG vaccination induration size of 14 mm or more.