Funding for this research was provided by:
the National Natural Scientific Foundation of China (30972556,81860588)
Basic Research Projects of Qinghai Province (2017-ZJ-770)
Direction projects of Qinghai province health and family planning commission (2017-wjzdx-38)
Received: 21 July 2018
Accepted: 24 August 2018
First Online: 4 September 2018
Ethics approval and consent to participate
: This study was in compliance with the ethical principles in the Declaration of Helsinki of the World Medical Association and was approved by the Ethics Committee of the Qinghai Institute for Endemic Disease Prevention and Control. All subjects signed an informed consent form.
: All authors read and approved the final manuscript.
: The authors declare that they have no competing interests.
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