1 Center for Postgraduate Education and Training, National Center for Child Health and Development, Tokyo, Japan.
2 Department of General Pediatrics and Interdisciplinary Medicine, National Center for Child Health and Development, Tokyo, Japan. nakao-h@ncchd.go.jp.
3 Division of Infectious Diseases, Department of Medical Specialties, National Center for Child Health and Development, Tokyo, Japan.
4 Department of General Pediatrics and Interdisciplinary Medicine, National Center for Child Health and Development, Tokyo, Japan.