1. Data Analysis Team, Epidemiological Investigation and Analysis Task Force, Central Disease Control Headquarters, Korea Disease Control and Prevention Agency, Cheongju, Korea.
2. Department of Pediatrics, Korea University Anam Hospital, Seoul, Korea.
3. Department of Pediatrics, Seoul National University College of Medicine, Seoul, Korea.
4. Department of Pediatrics, Pusan National University School of Medicine, Busan, Korea.
5. Department of Pediatrics, Seoul National University Bundang Hospital, Seongnam, Korea.