1. Department of Microbiology and Immunology, Keio University School of Medicine, Tokyo 160-8582, Japan
2. Department of Infectious Disease, Keio University Hospital, Tokyo 160-8582, Japan
3. Department of Hematology, Ogikubo Hospital, Tokyo 167-8515, Japan
4. Faculty of Nursing and Medical Care and Clinic for Infectious Diseases, Keio University, Fujisawa, Kanagawa 252-8530, Japan