Funding for this research was provided by:
National Natural Science Foundation of China (81502854)
Science and Technology Support Program of Guangzhou, China (201504291407178)
Text and Data Mining valid from 2018-04-02
Received: 24 July 2017
Accepted: 12 March 2018
First Online: 2 April 2018
Ethics approval and consent to participate
: Verbal and written informed consents were obtained from all participants in this study, with participants having the right to quit the questionnaire at any time. The study protocol was approved by the ethics review committee of the Guangzhou Center for Disease Control and Prevention.
: Not applicable.
: The authors declare that they have no competing interests.
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