1. Infectious Diseases Surveillance Center; National Institute of Infectious Diseases; Shinjuku-ku Tokyo 162-8640 Japan
2. Japan Poliomyelitis Research Institute; Higashimurayama Tokyo 189-0003 Japan
3. Department of Pediatrics; Civil Hospital Karachi; Karachi Pakistan
4. Department of International Health; Nagoya University School of Medicine; Aichi Nagoya 466-8560 Japan
5. Department of Microbiology; National Institute of Public Health; Minato-ku Tokyo 108-0071 Japan
6. Department of Virology II; National Institute of Infectious Diseases; Musashimurayama Tokyo 208-0011 Japan