1. Department of Trauma & Orthopaedics, Edinburgh University, Edinburgh Royal Infirmary, Little France, Ediburgh EH16 4SU, UK
2. Lothian University Hospitals Division, Edinburgh Royal Infirmary, Little France, Dalkeith Road, Edinburgh EH16 4SU, UK.
3. Laboratory of Healthcare-Associated Infection, Centre for Infections, Health Protection Agency, 61 Colindale Avenue, London, NW9 5EQ, UK.