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Article History

Received: 13 March 2017

Accepted: 12 February 2018

First Online: 20 February 2018

Ethics approval and consent to participate

: The study protocol was approved by community officials and the Ethics Committee of the University of Freiburg (Ref. No. 258/11_120365). Written informed consent was obtained from all individual participants included in the study.

: No individual details or images are included in the present study. Consent to publish in not required.

: The authors declare that they have no competing interests.

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