[1] UCL, Sch Med, London NW3 2PF, England
[2] Royal Free Hosp, Res Dept Infect & Populat Hlth, London, England
[3] Hlth Protect Agcy, Lab HealthCare Associated Infect, London, England
[4] Hlth Protect Agcy, Dept Healthcare Associated Infect & Antimicrobial, London, England
[5] Mahidol Univ, Trop Med Res Unit, Bangkok 10700, Thailand
[6] UCL, Dept Psychol, London NW3 2PF, England
[7] Univ Coll London Hosp, Dept Microbiol, London, England
[8] London Sch Hyg & Trop Med, Dept Publ Hlth & Policy, London, England
[9] Mid Essex NHS Trust, Dept Microbiol, Chelmsford, Essex, England