Funding for this research was provided by:
National Natural Science Foundation of China (71573290)
China Medical Board (17-271)
Received: 23 April 2018
Accepted: 11 June 2018
First Online: 26 June 2018
Ethics approval and consent to participate
: The study protocol was approved by the Human-Subject Research Project Institutional Review Board of School of Public Health, Sun Yat-sen University, China. All participants completed informed consent before being enrolled into the study.
: Not applicable.
: The authors declare that they have no competing interests.
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