1. Sakai City Institute of Public Health; Sakai Osaka 590-0953 Japan
2. School of Human Science and the Environment; University of Hyogo; Himeji Hyogo 670-0092 Japan
3. Division of Infectious Diseases; Children's Hospital Medical Center; Cincinnati Ohio 45229-3039 U.S.A.
4. Department of Molecular Virology and Microbiology; Baylor College of Medicine; Houston Texas 77030 U.S.A.