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 study was undertaken in a sample of 103 villages of 3 sub-divisions of Bangalore district as a part of the 5 year study of epidemiology of tuberculosis between 1961-68. The follow ups were done at 1.5, 3 & 5 years after the first survey. The entire population was offered tuberculin test with 1 TU RT 23, a second test with 20 TU RT 23 to those persons who were having reactions of 0-13 mm to 1 TU. All aged 5 years or more were offered 70mm photofluorograms at each survey. Two specimens of sputum were collected from persons having abnormal X-ray shadows for examination of tubercle bacilli. Procedures were uniform at each survey. The population was divided into three groups on the basis of their tuberculin reactions: (a) reactors to 1 TU (infected with M.tuberculosis), b) non-reactors to 1 TU but reactors to 20 TU (infected with atypical mycobacteria), c) non-reactors to both 1 TU & 20 TU (not infected with either M.tuberculosis or other mycobacteria). Incidence of disease and crude mortality were studied separately among these groups.

The five year incidence of culture positive disease was the highest among 1 TU reactors and the least among reactors to 20 TU. In the younger age group (5-14 years) the five year incidence of culture positive disease among reactors to 20 TU was significantly lower compared with that among 20 TU non-reactors. The reduction of incidence of culture positive cases in the former group over that in the latter was 75% for culture positive cases and 61% for combined culture positive and negative disease. As regards crude mortality, the overall rate was significantly lower among 20 TU reactors compared with non-reactors. Even if the significance of the finding on crude mortality is debatable, it could be concluded that non-specific infection provides some protection against development of tuberculosis, at least in younger age groups.

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.

The treatment results of an unsupervised Short Course Chemotherapy (SCC) regimen used under conditions of District Tuberculosis Programme (DTP) are presented. The District Tuberculosis Centre (DTC), Kolar and six of its Peripheral Health Institutions (PHIs) formed the study area. No extra efforts except ensuring of adequate availability of drugs at the participating centres were made to obtain patients' compliance. In all, 584 smear positive tuberculosis patients were diagnosed during the study period but 28.3% of the patients could not be initiated on treatment with the chosen self administered SCC regimen -2EHRZ/6TH(EH).

Of the 382 put on treatment, only 33.2% completed over 75% drug collections in both intensive and continuation phases. The pattern of treatment compliance did not vary with the place of treatment, i.e. DTC or PHI. Irrespective of treatment compliance, nearly 72-77% of the patients attained smear negative status at the end of the period of treatment, there being no difference between PHI and DTC. However, deaths were higher in the PHI patients. This could be attributed to a significantly higher proportion of aged patients taking treatment at PHI than at DTC. Considering death as an unfavourable outcome, overall favourable response was 65.9%. Patients with drug sensitive bacilli had a higher rate of culture negativity (70%), as compared to those with drug resistant bacilli (48%). It was concluded that unsupervised SCC could give encouraging results in a DTP setting, provided adequate drug supply was ensured.

Non-tuberculous Mycobacteria (NTM) that are present in the environment are responsible for induction of non-specific tuberculin sensitivity. They not only interfere with the results of tuberculin surveys, but are reported to influence the protective effect of BCG also. The prevalence and species distribution of NTM varies from place to place.

A study was carried out to find out the prevalence and identification of predominant species of NTM from the sputum specimens collected from chest symptomatics during an epidemiological survey in rural population of Bangalore district. Sputum specimens collected from 4015 tuberculin positive chest symptomatic persons were subjected for microscopy and culture for mycobacteria. Of the total 145 (3.6%) specimens showed growth of acid fast bacilli. Of them, 44 (30.3%) were M.tuberculosis and remaining 101 (69.7%) cultures were NTM. Specieswise distribution of NTM was as follows: 48% rapid growers, 26% scotochromogens and 22% non-chromogens. Most frequently isolated species were M.phlei (16.7%), M.gordonae (13.3%) and M.scrofulaceum. M.avium complex, M.xenopi, M.fortuitum complex and M.chelonei complex constituted 3.3% each.