Received: 27 August 2019
Accepted: 24 February 2020
First Online: 4 March 2020
Ethics approval and consent to participate
: The protocol for this study was approved by the ethics committee of Bielefeld University. Participants provided written informed consent for taking part in the study and being contacted for the follow-up.
: Not applicable.
: The authors declare that they have no competing interests. FF serves on the Editorial Board of BMC Public Health as Associate Editor.