Received: 2 November 2018
Accepted: 8 February 2019
First Online: 19 February 2019
Ethics approval and consent to participate
: The current study was performed according the principles of the Declaration of Helsinki. The final protocol was approved by the ethics committee of the University of Heidelberg, Heidelberg, Germany (S-421/2015).
: Not applicable.
: The authors declare that they have no competing interests.
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