Trends in the prevalence and incidence of tuberculosis in South India

OBJECTIVE: TO study trends in the prevalence and incidence of tuberculosis in south India. METHODS: Tn 1968-1970, about 100 000 subjects were surveyed for tuberculosi s and followed thereafter for 15 years, mainly by repeat survey once every 2.5 years. New entrants were inducted at every repeat survey. Radiographic examination of subjects aged 5 years or more and sputum smear and culture e xaminations of those with an abnormal shadow were undertaken; tuberculin te sts were done initially on all, and at 4, 10 and 15 years in selected sampl es of those aged 1-9 years. RESULTS: The prevalence of culture-positive tuberculosis decreased by 1.4% per annum to 634/100000, while that of smear-p ositive tuberculosis showed no significant decrease from 457/100000. The annual incidence of culture-po sitive tuberculosis decreased by 4.3 %/annum to 189/100000 and that of smea r-positive tuberculosis decreased by 2.3%/annum to 113/100000. Decreases in incidence occurred exclusively in those with abnormal radiographic finding s suggestive of tuberculosis at the start of the period. The annual risk of tuberculosis infection (ARTI) was initially 2%, and showed no sign of decl ine over the period. CONCLUSION: The prevalence of tuberculosis and ARTI showed little or no dec rease over the 15-year period. A significant decrease in incidence occurred , but exclusively in those with abnormal radiograph suggestive of tuberculo sis at the start of the period.