Received: 3 December 2020
Accepted: 22 January 2021
First Online: 19 February 2021
Ethics approval and consent to participate
: The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of Shaanxi Institute of Endemic Disease Prevention and Control (No. 2018 [CitationRef removed]). All subjects gave their informed consent for inclusion before they participated in the survey.
: Not applicable.
: The authors declare that they have no competing interests.