1. Section of Infectious Diseases and Immunity, Imperial College London
2. Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine
3. Centre for Sexual Health and HIV Research, Research Department of Infection and Population Health, Division of Population Health, University College London, London, UK
4. Research Service, Veterans Affairs Medical Center
5. Division of Infectious Diseases. Department of Internal Medicine, University of Cincinnati, Cincinnati, OH, USA
6. Department of Genitourinary Medicine, Mortimer Market Centre. Camden Provider Services NHS Trust, London, UK