Funding for this research was provided by:
Inner Mongolia Science and Technology Major Projects (none)
Received: 25 September 2018
Accepted: 17 March 2019
First Online: 30 April 2019
Ethics approval and consent to participate
: The study have been performed in accordance with the Declaration of Helsinki and approved by Inner Mongolia Center for Disease Control and Prevention and Inner Mongolia Medical University.
: Not applicable.
: The authors declare that they have no competing interests.
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