Received: 7 July 2018
Accepted: 23 July 2018
First Online: 11 October 2018
Ethics approval and consent to participate
: As the analysis was performed on anonymized non-genetic surveillance data, ethical consent was not required according to the Swiss law for research on humans (Art. 33 al. 2 LRH).
: Not applicable.
: The authors declare that they have no competing interests.
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