[1] Hlth Protect Agcy, Ctr Infect, Lab Healthcare Associated Infect, London NW9 5EQ, England
[2] Univ Utrecht, Dept Math, Utrecht, Netherlands
[3] Aberdeen Royal Infirm, Aberdeen, Scotland
[4] Statens Serum Inst, Natl Ctr Antimicrobials & Infect Control, DK-2300 Copenhagen, Denmark
[5] Erasmus MC, Dept Med Microbiol & Infect Dis, Rotterdam, Netherlands
[6] Univ Cattolica Sacro Cuore, Dept Infect Dis, I-20123 Milan, Italy