Received: 24 April 2020
Accepted: 12 June 2020
First Online: 3 July 2020
Ethics approval and consent to participate
: This study was conducted with the approval of the Epidemiological Research Ethics Review Committee of Hiroshima University (approval no. E-794).
: Due to retrospective studies, individual consent has not been obtained. It also gives them the opportunity to refuse if they do not want to provide data to this study.
: The authors declare that they have no competing interests.