Received: 13 November 2018
Accepted: 1 February 2019
First Online: 11 February 2019
Ethics approval and consent to participate
: The study was approved by the Cantonal Ethics Committee of Zurich (StV-No. 2009/14–0029). Formal patient consent was not required because of the retrospective study design.
: Not applicable
: The authors declare that they have no competing interests.
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