1. Department of Pediatrics Juntendo University Faculty of Medicine Bunkyo‐ku Tokyo Japan
2. Division of Pediatrics Tokyo Metropolitan Toshima Hospital Itabashi‐ku Tokyo Japan
3. Division of Obstetrics and Gynecology Tokyo Metropolitan Toshima Hospital Itabashi‐ku Tokyo Japan
4. Infectious Disease Surveillance Center National Institute of Infectious Diseases Shinjuku‐ku Tokyo Japan