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Article History

Received: 7 February 2018

Accepted: 26 February 2019

First Online: 5 March 2019

Ethics approval and consent to participate

: The study was approved by the medical ethics committee of the University of Oldenburg (reference no. 2017–032). All participants had to give written informed consent. Parental consent was obtained for study participants under 18 years of age.

: Not applicable.

: The authors declare that they have no competing interests.

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