Funding for this research was provided by:
National Natural Science Foundation of China (81601811, 81401715)
the Young Scholars fund of the Chinese Center for Disease Control and Prevention (2016A104)
grant-in-aid of Ministry of Health, Labor and Welfare, the Government of Japan (H23-Shinkou- shitei-020)
Received: 25 June 2018
Accepted: 13 March 2019
First Online: 25 March 2019
Ethics approval and consent to participate
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: Not applicable.
: The authors declare that they have no competing interests.
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