[1] Uppsala Univ, Uppsala, Sweden
[2] Inst Obstet & Gynecol DI Ott, St Petersburg, Russia
[3] Ctr Dis Control & Prevent, Atlanta, GA USA
[4] State Serum Inst, Copenhagen, Denmark
[5] Univ Hosp N Norway, Tromso, Norway
[6] Orebro Univ Hosp, Orebro, Sweden