Funding for this research was provided by:
The original project was supported by a cooperative agreement between the US Centers for Disease Control and Prevention and Peking University
Article History
Received: 31 October 2017
Revised: 1 July 2018
Accepted: 26 July 2018
First Online: 17 August 2018
Compliance with ethical standards
:
: The authors declare that they have no conflict of interest.