Thomas Locke BSc MBChB Foundation Year 1 doctor, Northern General Hospital, Sheffield, UK Dr Sally Keat BMedSci MBChB Foundation Year 1 doctor, Northern General Hospital, Sheffield, UK Andrew Walker BMedSci MBChB Specialist Trainee Year 1 doctor in Medicine, Chesterfield Royal Hospital, Chesterfield, Derbyshire, UK Rory Mackinnon BSc MBChB Foundation Year 2 doctor, Northern General Hospital, Sheffield, UK Editorial advisor: Professor R.C. Read Professor of Infectious Diseases, University of Sheffield, and Honorary Consultant Physician to the Central Sheffield Teaching Hospitals Trust, Royal Hallamshire Hospital, Sheffield, UK