Funding for this research was provided by:
National Natural Science Foundation of China (81101945)
Chongqing Municipal Public Health Bureau, Chongqing People's Municipal Government (CN) (2011-2-038)
Chongqing Science and Technology Commission (cstc2016jcjA0099)
Article History
Received: 28 March 2017
Accepted: 25 October 2017
First Online: 9 November 2017