S Mahalingam1, P Kalia2, A Nagendran2, P Oakeshott2. 1. Department of Population Health Sciences & Education, St Georges University of London, Cranmer Terrace, London SW17 0RE, UK. Electronic address: smahalingam@doctors.org.uk. 2. Department of Population Health Sciences & Education, St Georges University of London, Cranmer Terrace, London SW17 0RE, UK.