Footnotes

• Contributors SPP, HK and PKK planned and wrote the paper and revised the subsequent drafts. PAH and NG provided their expert opinion and helped in editing the manuscript. All authors have approved the final draft.

• 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 Commissioned; externally peer reviewed.