1. 1Department of Gastrointestinal, Emerging and Zoonotic Infections, Health Protection Agency, Centre for Infections
2. 2London Food, Water and Microbiological Services Laboratory, Health Protection Agency, Regional Microbiology Network, 61 Colindale Avenue, London NW9 5EQ, UK
3. 3Health Protection Agency, Regional Microbiology Network, London WC1V 7PP, UK