Received: 12 January 2017
Accepted: 11 January 2018
First Online: 29 January 2018
: The authors are staff members of the World Health Organization. The authors alone are responsible for the views expressed in this publication and they do not necessarily represent the views, decisions or policies of the World Health Organization.
: The Ethics Committee of Hospital Universitari Germans Trias i Pujol approved the study. Written informed consent was required for participants.
: Not applicable.
: The authors declare that they have no competing interests.
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