Funding for this research was provided by:
Natural Science Foundation of Guangdong Province (No.2019A1515011289)
National Natural Science Foundation of China (No.81700950)
Young Teacher Foundation of Sun Yat-sen University (No: 17ykpy74)
Grant-in-Aid from Health and Family Planning Commission of Guangdong Province (No.A2017579)
the Bureau of Health of the Guangzhou Municipality (No.20171A011324)
Text and Data Mining valid from 2019-12-01
Received: 24 September 2019
Revised: 4 November 2019
Accepted: 13 November 2019
First Online: 10 December 2019
Ethics approval and consent to participate
: The study had approval from the Ethics Committee of Sun Yat-Sen University.
: Not applicable.
: The authors declare that they have no competing interests.