Authors acknowledge the encouragement and support extended by Prof. (Dr) Balram Bhargava, Secretary to the Government of India, Department of Health Research, Ministry of Health and Family Welfare, and Director-General, Indian Council of Medical Research (ICMR), New Delhi, and Drs Raman Gangakhedkar and Nivedita Gupta, Division of Epidemiology & Communicable Diseases, ICMR, New Delhi.