Capital Institute of Pediatrics;
Beijing 100020;
China;
Beijing Children's Hospital attached to Capital Medical University;
Beijing 100045;
China;
GuangZhou Institute of Respiratory Diseases;
Guangzhou 510120;
Cruangdong;
China;
Children's Hospital of Chongqing Medical University;
Chongqing 400014;
China;
Chinese Centre for Disease Control and Prevention;
Beijing 100050;
China;