[1] Peterborough City Hosp, ITU, Edith Cavell Campus, Peterborough PE3 9GZ, Cambs, England
[2] Peterborough City Hosp, Anaesthet Dept, Peterborough, Cambs, England
[3] Worcester Acute Hosp, Dept Med, Worcester, Worcs, England
[4] New Cross Hosp, Dept Med, Wolverhampton, W Midlands, England
[5] Sandwell Hosp, Dept Med, Birmingham, W Midlands, England
[6] Arrowe Pk Hosp, Dept Surg, Liverpool, Merseyside, England
[7] Univ Birmingham, Dept Publ Hlth Epidemiol & Biostat, Birmingham, W Midlands, England