Footnotes

• Contributors BMI: this author helped with, literature search, manuscript preparation and review of manuscript. MCD: this author helped with, literature search, manuscript preparation and review of manuscript. MWS: this author helped with, literature search, manuscript preparation and review of 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.