Tuberculin tests repeated after an interval of time, at a different site have been reported to elicit reactions larger than the first test. A study was undertaken where reactors of 13mm or less to 1 TU have been tested with 20TU for the study of low grade reactions. Study was carried out in a previously untested and unvaccinated rural population (Longitudinal Survey), where only about 25% of the population showed 14mm or more to 1 TU and the remaining about 60% showed 10mm or larger reactions to 20 TU. These results confirm the high prevalence of non-specific allergy in the area.

It was found that a tuberculin test does enhance the allergy elicited by a subsequent test. The enhancing effect is associated with the initial allergy i,e., 8-13mm to 1 TU tuberculin, especially those elicited by a 20 TU test, increase being almost confined to those with 10mm and larger reactions to 20 TU. The enhancing effect increases with increase in age especially among those with 10mm or bigger reactions to 20 TU. It is possible that the enhancing effect is more in communities with high prevalence of non-specific allergy.

The report describes the changes that occurred during second survey carried out after an interval of one and half years in the cases diagnosed at the first survey done during 1961-62 from among a total population of about 62,000 in 119 villages in Bangalore District. It was observed that (1) Of the 62 sputum smear positive cases also having suggestive chest X-ray shadows, 34% had died, 35% were sputum positive and 31% had become culture negative after 1½ years. Of the 10 smear positive cases who were X-ray normal, non-e was culture positive at the start and 7 were negative by culture and smear after 1½ years. Of the 67 scanty smear positive cases (1 to 3 bacilli seen), only 3 were sputum positive, 10 were having X-ray shadows and half were tuberculin negative after 1½ years. (2) Of the 88 culture only positive cases (20 or more colonies and with X-ray evidence of disease) 31% had died and 47% continued to be sputum positive after 1½ years. A much smaller proportion of these changes occurred among culture positive cases with less than 20 colonies. (3) There were 457 persons having radiologically active tuberculosis on the basis of interpretation of a single X-ray picture by two independent readers but whose sputum were negative for AFB (suspect cases). Of these, 38% were tuberculin negative also. Of those suspect cases who were tuberculin positive, 9% become sputum positive after 1½ years, while only 2% of the tuberculin negative suspect cases became sputum positive.

It is concluded that there is a lot of variation in fate among the different categories of cases of pulmonary tuberculosis. Further, attention has been drawn to the possibility of self healing in about 30% of the bacillary cases after 1½ years.

The material on resistant strains of mycobacterium tuberculosis is derived from the longitudinal survey conducted from 1961-68 in a random sample of 133 villages of 3 taluks of Bangalore district. About 54,000 persons aged five years or more were surveyed 3 times at an interval of 18 months, two samples of sputum were collected from persons whose chest X-rays were judged to have abnormal shadows. The sputum specimens were examined by direct smear and culture and sensitivity tests were performed.

An attempt is made to study prevalence, fate, source and infectivity of resistant mycobacterium tuberculosis in three rounds. PREVALENCE: In the 3 rounds, 199, 194 and 176 cases respectively yielded positive cultures; Of them, 30, 36 and 53 cases were having resistant strains. At round III, the number of culture positive cases has not fallen significantly, but the number of strains resistant to INH alone has sharply increased (13, 18 & 35). Both findings are likely to be due to the treatment with INH alone offered at round II and also due to the fact that treatment was taken very irregularly. FATE: Over period of 3 years, of the cases with INH resistant strains, more than 1/3rd were dead, 1/4th continued to remain positive and resistant, and 1/4th became culture negative. Whereas, of the cases with strains sensitive to INH, less than 1/3rd were dead, 1/3rd became negative and the remaining were positive, 1/2 with sensitive strains and 1/2 with resistant strains. SOURCE OF CASES: The prevalence of cases with resistant strains at any one round is not due to the persistence of such cases from previous rounds but by development of new cases with such strains at each round. INFECTIVITY: The incidence of infection among contacts with sensitive strain was significantly more than among the contacts of cases with resistant strain. It is inferred that the infectivity of sensitive strains is more than that of the resistant strains.

Generally there is no acceptable definition of the term “case of pulmonary tuberculosis”, although such a definition is of fundamental importance both in clinical medicine where results of various chemotherapeutic regimens are compared, as well as for the comparison of different epidemiological data. The main purpose of this paper is to focus attention on the difficulties of defining a case on the basis of bacteriological examination, X-ray examination and tuberculin test. Data from two successive prevalence surveys in a random sample of 134 villages in Bangalore district with a population 70,000 have been utilized to illustrate some of the difficulties in defining a “case” of pulmonary tuberculosis for reporting the prevalence or incidence of the diseases. The entire population was tuberculin tested with 1 TU RT 23 with Tween 80 at both rounds and those 5 years of age and older were examined by 70mm photofluorogram. The sputum specimens (spot and overnight) were collected from those with any abnormality on X-ray as recorded by either of the two independent readers. Both the specimens were examined by fluorescent microscopy and Ziehl-Neelsen technique and by culture.

Analysis of data has shown that the term “a case of pulmonary tuberculosis” does not represent a single uniform entity, but embraces cases of several types, differing considerably in their tuberculin sensitivity, results of X-ray and sputum examination, in the reliability of their diagnosis and mortality experience. The status of cases found at initial and subsequent surveys showed changes with time, and such changes show considerable differences for the various types of cases. It was felt that a single straight-forward definition of a case was not possible to suit all situations. One has to use more than one definition. Although theoretically, finding a single bacillus in sputum should be adequate proof of pulmonary tuberculosis, it was shown that finding of a few bacilli (3 or less) was very often due to artifacts and should not be the basis for a diagnosis. It has also been found that positive radiological findings, in the absence of bacteriological confirmation, indicate only a high risk of the disease and not necessarily pulmonary tuberculosis. Direct microscopy appears to be a consistent index of disease but in community surveys has the limitation of missing a substantial proportion of cases and of adding some false ones.

In view of the difficulty of providing a single definition of a case of tuberculosis, four indices have been suggested. (1) Cases definitely positive by direct smear; (2) Cases definitely positive by culture; (3) All cases positive by culture (including less than twenty colonies); (4) Sputum positive cases which are radiologically active. Each of these could be used for different situations. However, it was concluded that, there seems to be no option but to use more than one definition for assessing the prevalence and incidence of disease.

The degree of the risk of infection and disease in man from drug resistant strains of mycobacterium tuberculosis is not clear. An increase in the prevalence of primary resistance indicates the extent of such risk while an increase of secondary or acquired resistance could be considered as a problem of the individual patient and may reflect limitations of his treatment.

The present report describes the prevalence of strains with acquired or primary resistance or of sensitive strains found in 3 successive surveys in a sizable random sample of village in a south Indian district. Changes in the status of cases with such strains from one survey to another and their infectivity among household contacts are also described. The prevalence of tuberculosis infection among household contacts of cases with acquired resistance to isoniazid was significantly higher than those with primary resistance or with sensitive culture. This was probably due to the longer duration of sputum positivity of isoniazid resistant strains at the time of diagnosis. But infectivity as judged by the incidence of new infection among household contacts was generally less for cases with acquired or primary resistance than for cases with sensitive cultures, though the difference observed was not statistically significant. A large number of culture positive cases especially those with primary resistance had no radiological evidence of active pulmonary tuberculosis. The prevalence of primary resistance was high in certain categories of cases and the differences between cases with primary resistance and those with acquired resistance were many and large. It was suggested that this could be due to the primary resistant cultures being those of atypical mycobacteria, despite positivity in the niacin test. There was a significant increase in the number of cases with acquired resistance to isoniazid at the third survey owing to the irregular treatment and supply of INH alone after the second round. The prevalence of primary resistance at the three rounds was almost the same.

Prevalence surveys are useful for estimating the tuberculosis problem in different countries. Three techniques are commonly used in surveys, tuberculin test, mass miniature radiography and sputum examination. Each has its own limitations. A limitation of sputum examination is that all the sputum positive cases in the community cannot be diagnosed when only one sample of sputum is examined from each eligible person. Multiple sputum examinations are not often possible under field conditions of surveys covering the whole community. It would be worthwhile to have some idea of the extent of under-diagnosis in sputum examination. For this purpose, during an epidemiological survey, four specimens of sputum were collected within seven days of X-ray examination from each person with an abnormal chest X-ray in 30 villages of a district of south India. Each specimen was examined by Fluorescent Microscopy (FM), Ziehl Neelson (ZN) technique and culture.

There were 34 culture positive cases among 2,164 persons for whom all the four culture examination results were available. Of them, 21 (62%) were found positive on one specimen. The second specimen increased the positivity to 32 (95%). Thus, for detecting both smear and culture positive cases two specimens are adequate. A third specimen is helpful for detecting cases positive by culture alone. An estimate of prevalence obtained from one sputum specimen can be estimated for the prevalence obtained from many specimens by applying correction factor of 1.67 and estimates based on two specimens by applying 1.26. Of the remaining 37 smear positive cases detected by one specimen, 20 were smear positive and culture negative. Of the remaining 17 smear positive and culture positive, 14(82%) were detected by one smear examination only.

ZN positives not confirmed by culture (mostly with less than four bacilli reported in the smear) increased from 7 from the first specimen to 18 from all four specimens, while positives confirmed by culture method showed only a marginal increase from 13 to 15. FM did not have this disadvantage as only two were culture negative among the 18 smear positive results by FM method. Examination of two specimens by FM detected about 95% of cases demonstrable by this method. But with the ZN technique additional specimens may add more “false positives”. Thus, for detecting cases both smear and culture-positive two specimens appear adequate. A third specimen is helpful for detecting cases positive on culture only.

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.