Molecular Characterization of Norovirus Causing Acute Gastroenteritis Outbreaks in Boarding Schools in Oyo State

Norovirus is the leading cause of non-bacterial acute gastroenteritis outbreaks worldwide, with closed institutional settings such as boarding schools representing high-risk environments for rapid person-to-person spread. This study molecularly characterized norovirus strains implicated in gastroenteritis outbreaks at two boarding secondary schools in Ibadan and Ogbomoso, Oyo State, Southwest Nigeria. Stool samples were collected from 85 students with acute diarrhea and vomiting during identified outbreak periods. Viral RNA was extracted from 10% stool suspensions using the QIAamp Viral RNA Mini Kit. RT-PCR targeting the ORF1/ORF2 junction region was performed for norovirus detection and genogroup classification. Positive samples were subjected to partial capsid (VP1) sequencing for genotyping. Norovirus was detected in 61.2% of symptomatic stool samples. Genogroup II genotype 4 (GII.4) was the predominant circulating strain (74%), consistent with its global epidemiological dominance. Secondary household transmission was reported in 18% of affected students during school breaks. The findings highlight the need for outbreak response protocols and improved water, sanitation, and hygiene (WASH) infrastructure in Oyo State boarding institutions. Keywords: norovirus, GII.4 genotype, gastroenteritis, boarding school, Oyo State.