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 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.

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.

Distribution of tuberculin test indurations were studied in relation to nutritional status of 930 rural children aged 1-4 years and 796 aged 5-9 years. Using Quetlet's Index, it has been observed that the distribution of indurations were similar in normal and malnourished children. By following Jelliffe's criteria of grading nutrition, no correlation was observed between the size of induration and degree of malnutrition. It is concluded that malnutrition in the community may not influence the prevalence rates of tuberculin infection based on such testing.