Footnotes

• Handling editor Tahir S Pillay.

• Contributors All authors contributed to the conceivement and design of the study and to the collection, analysis and interpretation of data. The manuscript was written by EA and MP and subsequently approved by all authors.

• 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 Not required.

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