Annual risk of tuberculous infection in four defined zones of India: a comparative picture

SETTING: Twenty-six selected districts in India. OBJECTIVES: To estimate the average annual risk of tuberculous infection (ARTI) in four defined zones in the country. STUDY DESIGN: A tuberculin survey was conducted in selected clusters of 26 districts in four defined zones of India. Children 1–9 years of age were subjected to tuberculin testing with 1TU PPD RT23 with Tween 80, and the maximum transverse diameter of induration was measured 72 h later. Prevalence of infection was estimated using the cut-off point method (Method I) and the mirror-image technique (Method II) among children without bacille Calmette-Guérin scar. Results from individual zones have been reported earlier, and the results from all four zones are presented here as a consolidated summary. RESULTS: The ARTI computed from estimated prevalence was found to be lowest in the southern zone (Method I: 1.1%, Method II: 1.0%). It was higher in the eastern zone (1.3% by both methods) and highest in the western (Method I: 1.8%, Method II: 1.6%) and northern zones (1.9% by both methods). The proportion of infected children was found to be significantly higher in urban than in rural areas in all zones. CONCLUSION: The intensified tuberculosis control efforts need to be sustained for many years