[1] Department of Bacteriology,
[2] National Institute of Public Health,undefined
[3] PO Box 4404 Nydalen,undefined
[4] 0403 Oslo,undefined
[5] Norway e-mail: per.sandven@folkehelsa.no Tel.: +47-22-042200 Fax: +47-22-042518,undefined
[6] Department of Surgical Oncology,undefined
[7] Norwegian Radium Hospital,undefined
[8] 0310 Oslo,undefined
[9] Norway,undefined