Footnotes

• Contributors All authors made substantial contributions to the conception and design of the work, and the acquisition, analysis and interpretation of data. All authors were involved in writing the drafts and approving the final manuscript.

• 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 consent for publication Not required.

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