1 Division of Clinical Epidemiology, Department of Medicine, McGill University Health Center, McGill University, V Building, Royal Victoria Hospital, 687 Pine Avenue West, Montreal, QC, Canada H3A 1A1.
2 Clinical Research Department, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK.
3 Division of Viral Hepatitis, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.
4 Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, E6531, Baltimore, MD 21205, USA.