Zhejiang University - Department of Infectious Diseases, Zhejiang Provincial Center for Disease Control and Prevention - Department of Infectious Diseases, Ningbo Women and Children's Hospital - Department of Infectious Diseases, Hangzhou XIXI Hospital (Hangzhou Sixth People’s Hospital) - Department of Infectious Diseases, Ruian People's Hospital - Department of Infectious Diseases, Wenzhou Medical University - Department of Pediatrics, Wenzhou Central Hospital - Department of Infectious Diseases, Huzhou Central Hospital - Department of Infectious Diseases, Zhoushan Women and Children's Hospital - Department of Pediatrics, Wenzhou Medical University - Department of Infectious Diseases, Yueqing People's Hospital - Department of Pediatrics, Government of the People's Republic of China - Department of Pediatrics, Government of the People's Republic of China - Department of Pediatrics, Shaoxing People's Hospital - Department of Infectious Diseases, First People's Hospital of Yuhang - Department of Pediatrics, Dongyang People's Hospital - Department of Infectious Diseases, Zhejiang University - Department of Critical Care Medicine, Zhejiang University - Children's Hospital, Zhejiang Provincial Center for Disease Control and Prevention - Department of Infectious Diseases, Zhejiang University - Statistics Unit, Zhejiang University - National Clinical Research Center for Child Health, Zhejiang University - Department of Respiratory and Zhejiang University - Children's Hospital