Received: 25 June 2019
Accepted: 20 September 2019
First Online: 6 November 2019
Ethics approval and consent to participate
: The study was performed in accordance with the declaration of Helsinki and was authorized by ethics committee of the University of Heidelberg, Germany (S-286/2010).
: Since the manuscript does not contain any individual person’s data in any form, consent for publication was not obtained.
: The authors declare that they have no competing interests.