[1] Publ Hlth Lab Serv, Ctr Communicable Dis Surveillance, London NW9 5EQ, England
[2] Bristol PHL, Bristol, Avon, England
[3] Liverpool PHL, Liverpool, Merseyside, England
[4] Liverpool Womens Hosp, Liverpool, Merseyside, England
[5] Arrowe Pk Hosp, Wirral, Merseyside, England
[6] Univ London St Georges Hosp, London, England
[7] PHLS Stat Unit, London, England