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.

Enhancing effect of tuberculin allergy as a result of repeat tests with 1 TU RT 23 on groups tested with I TU, 20 TU and placebo was studied by random allocation among population not vaccinated with BCG in 8 villages. In all, 2357 persons were tested with 1 TU and 759 with normal saline at first round. Based on testing at three rounds the study population could be divided into eight different groups and were labelled with alphabets 'a' to 'h' having been tested once, twice or thrice. The groups 'a', 'c', 'e' & ’g' were tested at 2 months, round two with 1 TU RT 23 and remaining half were not tested. However, all available persons in the 8 groups were retested at the third round, 18 months after the initial test. Thus, eight groups cannot be treated as independent samples but representative of the whole population.

The study did not show enhancing effect due to previous tuberculin test with 1 TU alone among groups tested once, twice or thrice after an interval of 18 months. Part of population was tested with 20 TU at round one; boosting effect was seen at 2 months when test was repeated. However, it was not seen after 18 months but when exactly the boosting effect disappeared was not known. Thus, there was no increase in reaction even among those who were tested with a higher dose of 20 TU earlier after 18 months. The groups provided the largest number for comparison between tested and the control groups. It is inferred from the study that boosting with high dose or repeat tests with the same dose does not persist after 18 months. Hence, for classifying positive tuberculin reactors, no correction is required to the same individuals/population after an interval of 18 months or more, as no boosting effect after 18 months has been observed, on the basis of this analysis.