Footnotes

• Handling editor Anna Maria Geretti

• Contributors DR, MR and RC designed the study. DR and MR analysed the data. DR, MR, RC, WR, SP, AB, KN and CF contributed to data collection and to 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.

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