1. University Division of Medicine, Bristol Royal Infirmary BS2 8HW, UK
2. Department of Microbiology, Bart's and the London NHS Trust, Smithfield, London EC1A 7BE
3. University Department of Obstetrics and Gynaecology, St Michael's Hospital, Southwell St, Bristol BS2 8EG
4. Centre for Biomedical Sciences, School of Applied Sciences, University of Wales Institute, Western Ave, Cardiff CF5 2YB
5. University Division of Medicine, Bristol Royal Infirmary BS2 8HW