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.

The fate of patients with isoniazid (H) resistant pulmonary tuberculosis, treated with 3 different Short Course Chemotherapy regimens (Regimen A-1 SHRZ/7TH, Regimen B-2SHR/6TH, Regimen C-2EHR/4H2R2) was examined in two sequential studies. One hundred H resistant patients belonging to two groups-one without history of previous treatment(core group) and second with history of previous treatment >=15 days (non-core group), were followed up at the end of 12th, 15th and 24th/36th month of chemotherapy. Bacteriological favourable response among patients in the core group at the end of chemotherapy with Regimen A, B and C were 65.2% of 23 patients, 50% of l8 patients, and 57.1% of 18 patients respectively. The response among patients in the non-core group were 27.3% with Regimen A and 52.6% with Regimen B.

At the end of 24/36th month of chemotherapy, 62.5% patients in the core group and 2 out of 7 in the non-core group on regimen A and 68.7% patients on regimen C in the core group and 5 out of 15 in the core group and 41.7% in the non-core group on regimen B were culture negative. The relapses were significantly high in regimen B & C in comparison with regimen A. Thus, of the total 100 patients, 99.3% were eligible for examination (1 died during chemotherapy), 67 were examined and of them 37 (62.7%) were culture negative, 22 positive and 8 were dead. The development of drug resistance to rifampicin was directly related to the duration of its use.

A comparative study to find out the prevalence of resistance to the major anti-TB drugs, SM, INH and PAS, under different situations was carried out. The situations considered were: (i) Sanatoria, (ii) Urban tuberculosis clinic, (iii) Rural general health dispensaries, (iv) the mass Case-finding among selected group of population and (v) survey of general population.

The prevalence of drug resistance to INH was 53%, the highest among sanatoria patients and 11%, the lowest among patients discovered in tuberculosis surveys i.e., situation (v). Among newly diagnosed culture positive tuberculosis patients of urban tuberculosis clinic, rural general health institutions and selected Case-finding programmes, i.e., situations (ii), (iii) and (iv), proportion of patients with INH resistant organisms were 26%, 33% and 16% respectively. The resistance rates were the highest in age group 25 to 44 in all 5 situations, case-wise rates were not significantly different. The prevalence of INH and streptomycin resistance among patients found in special mass Case-finding tuberculosis programme, were significantly lower than among patients attending special tuberculosis services or general health institutions.

The findings of this study show that prevalence of drug resistance among patients attending tuberculosis services and general health institutions is not a true index of the prevalence of drug resistance in the community and it varies under different situations.

A study was conducted to evaluate the usefulness of pyruvate medium for isolation of M.bovis from human material and additional yield of M. tuberculosis resistant to INH. Specimens from both rural and urban populations were included for this study in order to understand the problem in both the situations. There were two studies in progress at the National Tuberculosis Institute when pyruvate media slopes were introduced for culture purpose. One study was an epidemiological survey; 2518 sputum specimens received from 51 villages covering a population of about 32,300 were used. The specimens were collected from persons aged 5 years and above showing abnormal shadow on X-ray. The other study was conducted in collaboration with the State Tuberculosis Centre, Bangalore; 1204 sputum specimens were received from out patients attending the centre. In addition to LJ medium, pyruvate medium was used for isolation purposes. Identification and sensitivity tests were done on positive cultures as per routine. In all, 129 cultures of tubercle bacilli were isolated from 2118 specimens belonging to study 1 and 398 from 1204 specimens belonging to study 2. The number of cultures contaminated were 253 and 35 respectively. No M.bovis was isolated in either study. There were 24 and 23 cultures resistant to INH among those isolated from LJ and pyruvate medium respectively. Thus, no increase was observed in the isolation of INH resistant strains using pyruvate medium.

Hence, no benefit was derived by using this medium over and above what was obtained from plain Lowenstein Jensen medium in both the situations.