Received: 18 March 2019
Accepted: 31 July 2019
First Online: 14 August 2019
Ethics approval and consent to participate
: The study was approved by the ethics committee of the University Duisburg-Essen, need for consent was waived and the study was performed in accordance to the Declaration of Helsinki.
: Since there are no details on individuals reported within the manuscript consent for publication was waived.
: The authors declare that they have no competing interests.