Received: 3 November 2018
Accepted: 20 May 2019
First Online: 27 May 2019
Ethics approval and consent to participate
: The study was approved by the ethics committee of Shantou University Medical College. The need for consent was waived because of the retrospective data. Dr. Min Yu granted administrative permissions to access the raw data.
: Not applicable.
: The authors declare that they have no competing interests.