1. Colindale Microbiological Services, Health Protection Agency, Colindale, London NW9 5AT, UK
2. Department of Medical Microbiology, Royal Free Hospital NHS Trust, Pond Street, London NW3 2PF, UK
3. Centre for Clinical Microbiology, Department of Infection, Royal Free Campus, UCL, London NW3 2QG, UK
4. School of Medicine, University of St Andrews, North Haugh, St Andrews, Fife KY16 9TF, UK