The material on resistant strains of mycobacterium tuberculosis is derived from the longitudinal survey conducted from 1961-68 in a random sample of 133 villages of 3 taluks of Bangalore district. About 54,000 persons aged five years or more were surveyed 3 times at an interval of 18 months, two samples of sputum were collected from persons whose chest X-rays were judged to have abnormal shadows. The sputum specimens were examined by direct smear and culture and sensitivity tests were performed.

An attempt is made to study prevalence, fate, source and infectivity of resistant mycobacterium tuberculosis in three rounds. PREVALENCE: In the 3 rounds, 199, 194 and 176 cases respectively yielded positive cultures; Of them, 30, 36 and 53 cases were having resistant strains. At round III, the number of culture positive cases has not fallen significantly, but the number of strains resistant to INH alone has sharply increased (13, 18 & 35). Both findings are likely to be due to the treatment with INH alone offered at round II and also due to the fact that treatment was taken very irregularly. FATE: Over period of 3 years, of the cases with INH resistant strains, more than 1/3rd were dead, 1/4th continued to remain positive and resistant, and 1/4th became culture negative. Whereas, of the cases with strains sensitive to INH, less than 1/3rd were dead, 1/3rd became negative and the remaining were positive, 1/2 with sensitive strains and 1/2 with resistant strains. SOURCE OF CASES: The prevalence of cases with resistant strains at any one round is not due to the persistence of such cases from previous rounds but by development of new cases with such strains at each round. INFECTIVITY: The incidence of infection among contacts with sensitive strain was significantly more than among the contacts of cases with resistant strain. It is inferred that the infectivity of sensitive strains is more than that of the resistant strains.