[1] Turku Univ Hosp, Dept Pediat, Turku, Finland
[2] Univ Turku, Dept Virol, SF-20500 Turku, Finland
[3] Univ Wisconsin, Dept Pediat, Sch Med & Publ Hlth, Madison, WI USA
[4] Univ Wisconsin, Dept Med, Sch Med & Publ Hlth, Madison, WI USA
[5] Turku Univ Hosp, Div Microbiol & Genet, Dept Clin Virol, Turku, Finland