[1] Yamagata Prefectural Inst Publ Hlth, Dept Microbiol, Yamagata 9900031, Japan
[2] Katsushima Pediat Clin, Yamagata 9902461, Japan
[3] Yamanobe Pediat Clin, Yamagata 9900301, Japan
[4] Sendai Medial Ctr, Virus Res Ctr, Sendai, Miyagi 9838520, Japan
[5] Yamagata Univ, Course Clin Nursing, Fac Med, Yamagata 9909585, Japan
[6] Yamagata Univ, Dept Infect Dis, Fac Med, Yamagata 9909585, Japan
[7] Natl Inst Infect Dis, Dept Virol 2, Tokyo 2080011, Japan