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

In 1968-1970, about 100,000 subjects were surveyed for tuberculosis 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 examinations of those with an abnormal shadow were undertaken; tuberculin tests were done initially on all, and at 4, 10 and 15 years in selected samples of those aged 1-9 years.

RESULTS

The prevalence of culture-positive tuberculosis decreased by 1.4% per annum to 694/100,000, while that of smear-positive tuberculosis showed no significant decrease from 457/100,000. The annual incidence of culture-positive tuberculosis decreased by 4.3%/annum to 189/100,000 and that of smear-positive tuberculosis decreased by 2.3%/annum to 113/100,000. Decreases in incidence occurred exclusively in those with abnormal radiographic findings suggestive of tuberculosis at the start of the period. The annual risk of tuberculosis infection (ARTI) was initially 2%, and showed no sign of decline over the period.

CONCLUSION

The prevalence of tuberculosis and ARTI showed little or no decrease over the 15-year period. A significant decrease in incidence occurred, but exclusively in those with abnormal radiograph suggestive of tuberculosis at the start of the period.