Footnotes

• Handling editor Tahir S Pillay.

• Twitter @simonroymd

• Contributors SFR and MJC designed the study, collected data and wrote the 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; internally peer reviewed.