1. Department of Pediatric Surgery, Okayama Medical Center, National Hospital Organization, Okayama, Japan
2. Department of Human Ecology, Okayama University Graduate School of Environmental and Life Science, Okayama, Japan
3. Department of Pediatrics, Okayama Medical Center, National Hospital Organization, Okayama, Japan
4. Department of Epidemiology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan