Funding for this research was provided by:
Medical Research Council (MR/M021513/1)
Received: 13 February 2019
Accepted: 21 June 2019
First Online: 3 July 2019
Ethics approval and consent to participate
: Ethical approval was granted by the Ethical Committee of School of Public Health of Sun Yat-sen University in China. Written consent was obtained from all individual participants included in the study.
: Not applicable.
: The authors declare no conflict of interest.