[1] Natl Inst Infect Dis, Dept Virol 1, Tokyo 1628640, Japan
[2] Univ Tokyo, Dept Pediat, Tokyo, Japan
[3] Asahikawa Med Univ, Dept Pediat, Asahikawa, Hokkaido, Japan
[4] Fukushima Med Univ, Dept Microbiol, Fukushima, Japan
[5] Natl Ctr Child Hlth & Dev, Dept Maternal & Perinatal Serv, Tokyo, Japan
[6] Kobe Univ, Dept Pediat, Kobe, Hyogo 657, Japan
[7] Kyorin Univ, Dept Pediat, Tokyo, Japan
[8] Natl Ctr Child Hlth & Dev, Dept Infect Dis, Tokyo, Japan
[9] Kobe Univ, Dept Obstet & Gynecol, Kobe, Hyogo 657, Japan