Received: 6 December 2018
Accepted: 6 February 2019
First Online: 21 February 2019
Ethics approval and consent to participate
: Ethical approval was granted by Jiading district center for disease control and prevention research ethics committee. All subjects gave verbal and written informed consent to participate in the study, they would like to participate in investigation and answer all the related questions in the questionnaire. The survey was conducted by a full-time investigator using a questionnaire and face-to-face inquiries.
: Not applicable.
: The authors declare that they have no competing interests.
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