1. Department of Infectious Diseases, Yamagata University Faculty of Medicine, Yamagata 990-9585, Japan
2. Department of Microbiology, Yamagata Prefectural Institute of Public Health, Yamagata 990-0031, Japan
3. Yamanobe Pediatric Clinic, Yamanobe 990-0301, Japan
4. Katsushima Pediatric Clinic, Yamagata 990-2461, Japan