Received: 1 August 2017
Accepted: 11 April 2019
First Online: 16 May 2019
Ethics approval and consent to participate
: Participation in this study was voluntary. Prior to the commencement of the first visit, written informed consent was required from each subject or the parents of children under the age of 18 years. The study was approved by the ethics committee of Goethe University (reference number 208/13).
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.