Received: 7 February 2019
Accepted: 12 July 2019
First Online: 18 July 2019
Ethics approval and consent to participate
: The Ethics Committee of each participating center approved the study protocol. The procedures were in accordance with the ethical standards of the Declaration of Helsinki; specific written informed consent from parents and from children over 12 years was obtained.
: Not applicable.
: The authors declare that they have no competing interests.