[1] Natl Publ Hlth Inst, Oulu 90101, Finland
[2] Natl Publ Hlth Inst, Helsinki, Finland
[3] Univ Hosp Oulu, Clin Microbiol Lab, Oulu, Finland
[4] Univ Helsinki, Dept Obstet & Gynecol, Helsinki, Finland
[5] Montana State Univ, Dept Microbiol, Bozeman, MT 59717 USA
[6] Univ Oulu, Dept Med Microbiol, Oulu, Finland