Authors’ contributions
Haitao Yuan, Gaohua Li, Zhenzhao Xu and Jinfan Zhou were responsible for data collection. Xuehua Zhang, Zilin Tang, Jie Fu and Mingyi Wu were responsible for data analysis and will contribute to the interpretation of data. Xuehua Zhang, Haitao Yuan and Zilin Tang wrote the manuscript, which was critically revised by Jiafei Xi and Yanan Wang. All authors have approved the final version of the manuscript.