Twenty-year trend of chronic excretors of tubercle bacilli based on the nationwide tuberculosis prevalence surveys in Korea, 1975-1995

SETTING: A study of chronic excretors of tubercle bacilli (chronic cases) b ased on the nationwide random sample surveys of tuberculosis prevalence con ducted in Korea from 1975 through 1995. OBJECTIVE: To investigate the temporal trend of the prevalence of chronic c ases, and to match these with treatment outcomes and drug resistance rates. DESIGN: Bacillary cases were classified by history of chemotherapy into new (those who denied a history of chemotherapy), non-chronic (those who had t aken chemotherapy for less than 2 years) and chronic cases (those who had t aken chemotherapy for more than 2 years). RESULTS: Chronic cases decreased from 107 to 12 per 100 000 population (ann ual rate of reduction [ARR] 11.89%) over the 20-year period. The ARR of chr onic cases was significantly greater than that of new cases, and accelerate d from 1985 (ARR 15.83%), after the application of short course chemotherap y. Rates of overall drug resistance rates increased up to 1980, and those o f multidrug resistance up to 1985, followed by a decrease thereafter. A red uction in chronic cases was observed even during the period of increase in drug resistance (including multidrug resistance). CONCLUSION: The prevalence of chronic tuberculosis cases has decreased due to improvements in overall treatment outcome.