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.