The findings in a highly selected group of patients, such as those attending clinics or sanatoria, cannot be used as the basis for assessing the true prevalence of strains of Mycobacterium tuberculosis with acquired or primary resistance or of sensitive strains in a community. The present report describes the prevalence of such strains as found in 3 successive surveys in a sizeable random sample of villages in a South Indian district. Changes in the status of cases with such strains from an earlier survey to a later one and the status at an earlier round of cases found at a later one are also described.The prevalence of tuberculous infection among household contacts of cases with acquired resistance to isoniazid was significantly higher than that among contacts of cases with primary resistance or of those with sensitive cultures. This is probably due to the longer duration of sputum positivity of the former at the time of diagnosis. But infectivity, as judged by the incidence of new infections among household contacts, was generally less for cases with acquired or primary resistance than for cases with sensitive cultures, though the difference 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 very high among certain categories of cases, and the differences between cases with primary resistance and those with acquired resistance were many and large. It is suggested that this could be due to some of 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 round owing to irregular treatment with that drug after the second round. The prevalence of primary resistance at the 3 rounds was almost the same.

Aminosalicylic Acids↗

PubMed1968

Problems in defining a "case" of pulmonary tuberculosis in prevalence surveys.

An analysis of data from two successive tuberculosis prevalence surveys (conducted at an interval of 18 months) in a random sample of villages in Bangalore District, South India, has shown that the term "a case of pulmonary tuberculosis" does not represent a single uniform entity, but rather embraces cases of several types, differing considerably in their mortality experience, tuberculin sensitivity, results of X-ray and sputum examinations, and in the reliability of their diagnosis.The status at the first survey of the cases found at the resurvey and that at resurvey of those found at the initial survey give an indication of changes with time. Such changes show considerable differences for the various types of cases and provide another dimension to study the differences among them. The authors consider that, in spite of the great need and importance of a single straightforward definition of a case, no such definition is suitable for all situations; there is no other option but to continue to use more than one definition.Although, theoretically, finding a single bacillus in the sputum should be adequate proof of pulmonary tuberculosis, it is shown that finding of a few bacilli, 3 or less, is probably far too often due to artefacts and should not be the basis for a diagnosis.The findings also well bear out the notion that positive radiological findings, in the absence of bacteriological confirmation, indicate, not pulmonary tuberculosis, but only a high risk of the disease. Direct microscopy appears to be a consistent index of disease but, in community surveys, has the limitations of missing a substantial proportion of cases and of adding some false cases. The extent of these limitations, so far as symptomatic patients in a community tuberculosis control programme are concerned, remains to be investigated.

Female↗

PubMed1966

Problems connected with estimating the incidence of tuberculosis infection.

Many problems have to be faced in the estimation of an apparently simple but valuable index-namely, the incidence of tuberculosis infection. Very little attention seems to have been paid to these problems so far.Records from 50 villages in a district of South India, whose populations were tested with 1 TU of PPD RT 23 in Tween 80 diluent and retested after 18 months, have been examined for a reappraisal of existing methods. As a result, it has been found that some of these methods are subject to gross errors and that available figures are unreliable.For estimating the newly infected, a new approach based on the drawing of a curve for the distribution of differences in reaction size from one round of tuberculin testing to another is presented. Further, it is shown that the newly infected probably constitute a homogeneous group with an increase in mean reaction size of about 24 mm and standard deviation of 4 mm. Accordingly, 98% of the newly infected show an increase in reaction size of 16 mm or more. There are others who show similarly large increases in allergy on a retest, even in the absence of infection. The number of persons in the latter category rises with age and is likely to be greater in areas with a high prevalence of non-specific allergy.

Adolescent↗

PubMed1966

Enhancing of tuberculin allergy by previous tuberculin testing.

A controlled study on the enhancing of tuberculin allergy by one or more earlier tuberculin tests was carried out in a previously untested and unvaccinated population, in an area where the prevalence of non-specific allergy was known to be high. The results have shown that a test with 1 TU of PPD RT 23 in Tween 80 diluent causes subsequent tests to elicit significantly larger reactions. This enhancing effect is more marked among those with initial reactions of 8-13 mm to 1 TU or 10 mm and more to 20 TU. There is practically no enhancement among those whose reactions to 20 TU measure 0-4 mm or even 0-9 mm. Even in the group with reactions of 10 mm and more to 20 TU only some individuals show evidence of enhancement. The enhancing of allergy increases with age.The addition of a 20 TU test increases the enhancement of allergy but mostly among those with reactions of 8-13 mm to 1 TU.The findings suggest that enhancement may be more marked in communities with a high prevalence of non-specific allergy.

Female↗

PubMed1966

Distribution of tuberculous infection and disease among households in a rural community.

Clinical experience has led to a strong belief that tuberculosis is a family disease and contact examination is a sine qua non for case-finding programmes. Considerable doubts are cast on the usefulness of contact examination in tuberculosis control by the present study, which is based on a sample of an entire population rather than on family contacts of known cases only. Cases of tuberculosis occurred mostly singly in households, and contact examination could have revealed only a very small percentage of the cases in this community.Another common belief is that the prevalence of infection among children under five years of age is a good index of disease in households. In this study, however, a large proportion of households with cases of tuberculosis had no children of this age, and even in homes with a bacteriologically confirmed case, about 88% of the children did not show evidence of infection.The tuberculin reactions of infected contacts were, on the average, slightly larger than those among non-contacts. Further, the proportion of large tuberculin reactions among infected persons was found to be greater in the younger age-groups than in the older age-groups. This finding has been taken to indicate that new infection gives rise to large reactions that subsequently wane to some extent in persons not constantly exposed to infection, such as, for example, the members of households without cases.

Adolescent↗