Change in the risk of tuberculous infection over an 8-year period among schoolchildren in Bangalore City.

Setting: Bangalore City, South India.

Objective: To estimate the trends in transmission of tuberculous infection.

Methods: Two tuberculin surveys were carried out among children attending grades 1 and 2 of 60 selected schools at an interval of 8.3 years, corresponding to the period of DOTS expansion. Tuberculin testing was carried out using 1 tuberculin unit (TU) of purified protein derivative (PPD) RT 23 with Tween 80, and the maximum transverse diameter of induration was recorded about 72 h later. As the reactions due to infection with tubercle bacilli could not be clearly delineated from cross-reactions on the frequency distributions of tuberculin reaction sizes at either survey, the prevalence of tuberculin reactions > or = 10 mm, > or = 12 mm and > or = 14 mm in size were compared between the two surveys. The annual risk of tuberculous infection (ARTI) was computed from the estimated prevalence of reactions > or = 14 mm in size.

Results: Estimates of prevalence of reactions at all chosen cut-off points were lower at Survey II compared to Survey I. These differences were statistically significant. An average per annum decline in ARTI of about 4% was observed between the two surveys.

Conclusion: Tuberculosis control measures should be further intensified to enhance the rate of decline in transmission of infection.