Received: 7 July 2017
Accepted: 19 December 2017
First Online: 10 February 2018
Ethics approval and consent to participate
: Ethical approval was obtained from the Cross River State Ministry of Health, before collection of the samples. Informed consent was obtained from the school proprietor, the head teacher, and pupils in the selected schools.
: Not applicable
: The authors declare that they have no competing interests.
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