Funding for this research was provided by:
The National Key Research and Development Program of China (2016YFE0201500)
The Innovation Project of Shandong Academy of Medical Sciences
The Syphilis and Other Sexually Transmitted Diseases Control Research in Shandong
Received: 23 June 2018
Accepted: 3 October 2018
First Online: 26 October 2018
Ethics approval and consent to participate
: This study was conducted in accordance with the ethical principles stated in the Helsinki Declaration. This study was reviews and approved by the Ethics Committee of Shandong Provincial Institute of Dermatology and Venereology (approval number: 2016–04). There were several sensitive questions related to sex in the questionnaires. Participants may refuse to answer those questions or provide untruthful information if they signed informed consent. In order to obtain true and accurate information, oral informed consent instead of written consent was obtained from each participant by interviewers before interview. This procedure was approved by the ethics committee. The name was not written on the questionnaire and the confidentiality of the data was kept properly.
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.