1 Centre for Adolescent Health, Department of Paediatrics, University of Melbourne, Murdoch Childrens Research Institute, Royal Children's Hospital, Parkville, VIC 3052, Australia. Electronic address: george.patton@rch.org.au.
2 Department of Infectious Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK.
3 Mailman School of Public Health, Columbia University, New York, NY, USA.
4 Centre for Adolescent Health, Department of Paediatrics, University of Melbourne, Murdoch Childrens Research Institute, Royal Children's Hospital, Parkville, VIC 3052, Australia.
5 University College London Institute of Child Health, London, UK.