Funding for this research was provided by:
Beijing Medical and Health Foundation (MH180924)
Received: 4 September 2018
Accepted: 4 January 2019
First Online: 11 January 2019
Ethics approval and consent to participate
: The study was reviewed and approved by the Ethics Committee (IRB) at the Public Health School of Peking Union Medical College. All study participants read and signed a written informed consent prior to recruitment into the study.
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.