Footnotes

• ESPM and MJB contributed equally.

• Contributors ESPM contributed to the conception and design of the study, acquisition and analysis of data and drafting of the manuscript. MJB contributed to the conception and design of the study, analysis of data and drafting of the manuscript and figures. PC contributed to acquisition and analysis of data and drafting of the manuscript. NK contributed to acquisition of data and drafting of the manuscript. DK conceived the study and contributed to the acquisition and analysis of data and drafting of the manuscript and figures, and approved the final version. All authors critically reviewed and approved of 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.

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