Annual risk of tuberculous infection in rural areas of Uttar Pradesh, India

SETTING: Rural areas in Uttar Pradesh, the most populous state in India. OBJECTIVES: 1) To estimate the average annual risk of tuberculous infection (ARI), 2) to study ARI trends with age, and 3) to compare tuberculin reactions among children with and without BCG scar. STUDY DESIGN: A cross-sectional tuberculin survey was conducted among children aged 1-9 years residing in Rae Bareli, Hardoi and jaunpur districts, Uttar Pradesh. Tuberculin testing was performed using 1TU of PPD RT23 with Tween 80, and indurations were measured 72 hours later. Prevalence of infection was estimated in children without BCG scar based on the cut-off point identified on the frequency distribution of reaction sizes. The ARI was computed from the estimated prevalence. RESULTS: The proportion of children with BCG scar varied from 25% to 31% in the study districts. Using a cut-off of 14 mm among children without BCG scar, the ARI was estimated at 2.3% in Rae Barell, 1.9% in Hardoi and 1.5% in jaunpur, and was observed to increase with age. Tuberculin test results among children with BCG scar suggest that they may be included in tuberculin surveys to estimate ARI. CONCLUSION: High rates of transmission of tuberculous infection suggest that tuberculosis control measures need to be intensified.