1. University of Manchester, North Manchester General Hospital, Delauneys Road, Crumpsall, Manchester M8 6RL, UK.
2. Public Health Laboratory, Withington Hospital, Manchester M20 2LR, UK.
3. Stepping Hill Hospital, Poplar Grove, Stockport, Cheshire SK2 7JE, UK.
4. Princess Margaret Rose Orthopaedic Hospital, Fairmilehead, Edinburgh EH10 7ED, UK.