Footnotes

• Contributors YZ and ZS designed the study and wrote the letter. YZ and ZS analysed the data. YZ, JW, LZ and JX performed the online medical service.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

• Patient consent for publication Not required.

• Provenance and peer review Not commissioned; internally peer reviewed.