A large outbreak of acute gastroenteritis caused by rare group C rotavirus in schoolchildren in Yunnan, China: Clinical, epidemiological, and genomic characterization.

We investigated the etiology, molecular epidemiology, and glycan-binding architecture of an acute gastroenteritis (AGE) outbreak among students at a primary school in Yunnan Province, China. After an institutional outbreak was declared in March 2025, we conducted epidemiological investigations and collected 25 specimens. The specimens were screened for enteric pathogens using multiplex real-time RT-PCR. Near-complete genomes were generated from three group C rotavirus (RVC) positive stool samples, and all 11 genome segments were analyzed phylogenetically. The VP8* domain of strain YN03 was modeled with AlphaFold3 and characterized structurally. No bacterial or alternative viral pathogens were detected. RVC RNA was detected in all 20 fecal samples and one rice sample. The outbreak strain had a monotypic G4-P [2]-I2-R2-C2-M2-A2-N2-T2-E2-H2 constellation, with ≥99.8% intra-outbreak nucleotide identity. VP7 and VP4 clustered within sub-lineages G4-III and P [2]-II, respectively, sharing 98.3%-98.8% identity with contemporary isolates from Europe and South and North Asia, but less than 94.7% identity with the earlier Chinese reference strain SZ94. Clinical manifestations were mild; abdominal pain was the most common symptom (76.7%), followed by vomiting (34.9%) and diarrhea (30.1%). Ten amino acid substitutions were identified in YN03 VP8*. Structural modeling revealed conservation of the topology and electrostatic surface properties of the type A glycan-binding pocket, and glycan-array analysis demonstrated binding of YN03 VP8* to the type A antigen. This study provides the first complete genomic characterization of an RVC outbreak in Yunnan and highlights the epidemic potential of G4P [2] strains, the need to include RVC in routine diagnostics, and priorities for future vaccine development.