Footnotes

• Contributors SS and CM were involved in study design, data collection, statistical analysis and preparation of the article. SF was involved in study design and preparation of the article.

• 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.