Article History
Received: 12 March 2019
Accepted: 29 July 2019
First Online: 14 August 2019
Compliance with ethical standards
:
: The authors declare that they have no competing interests.
: This study was approved by the Ethics Committee of West China Hospital of Sichuan University. As this is a retrospective study, informed consent was not essential in line with the Ethical Guidelines for Epidemiological Research.The study was permitted by the Ethics Committee of West China, Sichuan University.
: Not applicable.