Received: 17 June 2019
Accepted: 16 September 2019
First Online: 17 October 2019
Ethics approval and consent to participate
: This study was approved by the institutional research board of Niigata University School of Medicine (approval number: 2017-0344). The need for informed consent was waived because this study was a retrospective cross-sectional study.
: Not applicable.
: The authors declare that they have no competing interests.