Received: 21 March 2021
Accepted: 25 June 2021
First Online: 14 July 2021
: The written informed consent was obtained from all parents and guardians of the children before sample collection and epidemiology investigation. Ethical approval for study, to perform molecular analyses on the samples was obtained from the Ethics Committee of Tianjin Children’s Hospital. Furthermore, permission to collect data, samples from patients and subsequent analysis was sought from Tianjin Children’s Hospital. This study was conducted according to the priciples expressed in the Declaration of Helsinki.
: Not applicable.
: The authors declare that they have no competing interests.