Disease Control and Prevention Center, National Center for Global Health and Medicine, Tokyo, Japan
Masahiro Ishikane
Corresponding author. M. Ishikane; Tel.: +81-3-3202-7181; fax: +81-3-3207-1038.; Disease Control and Prevention Center, National Center for Global Health and Medicine, Tokyo, Japan
Mugen Ujiie
Disease Control and Prevention Center, National Center for Global Health and Medicine, Tokyo, Japan
Norio Ohmagari
Disease Control and Prevention Center, National Center for Global Health and Medicine, Tokyo, Japan