Received: 27 June 2018
Accepted: 6 September 2019
First Online: 11 October 2019
Ethics approval and consent to participate
: This study was approved by the Ethical Review Board of the Canton of Zurich, Switzerland, and was performed in full accordance with the Declaration of Helsinki (2015–0322). All parents provided written informed consent after study procedures and aims had been explained in detail. All children provided verbal assent, while adolescents older than 14 years of age also provided written informed consent.
: Not applicable.
: The authors declare that they have no competing interests.