Received: 18 March 2019
Accepted: 5 June 2019
First Online: 14 June 2019
Ethics approval and consent to participate
: The study was approved by the Faculty of Medicine and Health Sciences, Sana’a University and heads of schools. Before samples collection, students’ parents gave a written informed consent. School children gave a verbal consent which was approved for children by the ethical committee after their parents gave a written informed consent.
: Not applicable.
: The authors declare that they have no competing interests.