Abstract
1 Division of Epidemiology, Department of Infectious Diseases, Oita Medical University, Hasama-machi, Oita 879-5593, Japan
4 Research Center for Asian and Caribbean Diseases, Oita Medical University, Hasama-machi, Oita 879-5593, Japan
2 First Department of Internal Medicine, Faculty of Medicine, University of the Ryukyus, 207 Uehara, Nishihara, Okinawa 903-0215, Japan
3 Department of Virology, Faculty of Medicine, University of the Ryukyus, 207 Uehara, Nishihara, Okinawa 903-0215, Japan