Received: 15 December 2019
Accepted: 20 April 2020
First Online: 6 May 2020
Ethics approval and consent to participate
: This study was reviewed and approved by the Ethics Committee Zurich [Kanton Zürich] (committee’s reference number: KEK-ZH-NR 2014–0480). The study complied with the Helsinki Declaration of 1975, revised in 2008. This is a retrospective study. For this type of study formal consent is not required.
: Not applicable.
: All authors declare that they have no competing interests.