Received: 22 July 2019
Accepted: 15 October 2019
First Online: 31 October 2019
Ethics approval and consent to participate
: This study was approved by the ethics board of each hospital and by the Chadian Ministry of Public Health (N<sup>o</sup> 676/PR/PM/MSP/SE/SG/DRGP/DRH/ SGF/16). Informed written consent was obtained from all subjects and from at least one parent for each child before enrolment in the study.
: Not applicable.
: The authors declare that they have no competing interests.