1. Department of Pediatrics, Graduate School of Medicine, Chiba University, Chiba 260-8670, Japan.
2. Department of Public Health, Hyogo College of Medicine, Nishinomiya, Hyogo Prefecture 663-8131, Japan.
3. Department of Allergy, Chiba Aoba Municipal Hospital, Chiba 260-8722, Japan.
4. Department of Pediatrics, Shimoshizu National Hospital, Chiba 284-0003, Japan.