Funding for this research was provided by:
National Natural Science Foundation of China (71702131, 71373146)
China Scholarship Council (201706220244)
Article History
Received: 27 August 2018
Accepted: 9 May 2019
First Online: 23 May 2019
Ethics approval and consent to participate
: Participants were informed that they could refuse to answer any question. The questionnaire did not ask about infection status, and no biological samples were collected. The consent obtained from participants was written. The project was approved by the Medical Ethics Committee at the Shandong University School of Medicine (Grant No. 201001052).
: Not applicable.
: None of the authors has any conflicts of interest.
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