S M Langan1, E I Benchimol2,3. 1. London School of Hygiene and Tropical Medicine, London, U.K. Sinead.Langan@lshtm.ac.uk. 2. Children's Hospital of Eastern Ontario (CHEO) Research Institute, Ottawa, Ontario, Canada. 3. School of Epidemiology, Public Health and Preventive Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Canada.