Article History
Received: 14 January 2019
Accepted: 15 May 2019
First Online: 23 May 2019
Ethics approval and consent to participate
: The study was approved by the institutional review board of Seoul Medical Center (IRB no. 2017–07-002). All of the workers participated voluntarily and provided written informed consent.
: Not applicable.
: The authors declare that they have no competing interests.
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