Footnotes

• Contributors KK and KEZ reviewed the relevant articles. KK analysed the data and drafted the manuscript. DP interpreted the data and revised the manuscript. All authors read and approved 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; internally peer reviewed.