Abstract
PHLS Food Safety Microbiology Laboratory, Central Public Health Laboratory and *Environmental Surveillance Unit, Communicable Disease Surveillance Centre, 61 Colindale Ave, London NW9 5HT, †Birkenhead & Wallasey Primary Care Trust, St Catherine's Hospital, Birkenhead, Merseyside CH42 0LP, ‡Communicable Disease Surveillance Centre (North West), Chester CH1 4EF, South Sefton Primary Care Trust, Burlington House, Crosby Road North, Waterloo, Liverpool L22 0QB and ||Department of Public Health North West Region, Millennium Park, Birchwood, Warrington WA3 7QN
Corresponding author: Dr J. McLauchlin (e-mail: jmclauchlin{at}phls.org.uk ).