Epidemiological investigation of an acute gastroenteritis outbreak associated with norovirus GΙΙ.17[P17] in a cross-border travel group - Shanghai Port, China, 2024

BACKGROUND: Norovirus is a leading cause of acute gastroenteritis and spreads efficiently in closed, mobile cohorts such as organized travel groups. This case is notable for the real-time detection and genomic confirmation of a cross-border outbreak at a port of entry, including near-identical Norovirus GΙΙ.17[P17] genomes and documented asymptomatic carriage, illustrating the practical value of integrated metagenomic surveillance in border health operations. CASE PRESENTATION: On July 21, 2024, 26 travelers arrived at Shanghai Port after a 12-day group tour in Europe. Clinical interviews identified 15 individuals (57.7%) with diarrhea, nausea, dizziness, and abdominal pain; no hospitalizations occurred. On-site anal swab testing was negative for SARS-CoV-2, influenza A and B, Vibrio cholerae, and Escherichia coli. RT-qPCR detected Norovirus GII in 10 samples (38.5%), including two asymptomatic individuals. Metagenomic sequencing generated near-complete genomes for all RT-qPCR-positive samples, which were 99.9-100% identical and classified as Norovirus GΙΙ.17[P17], confirming a cross-border outbreak within the travel cohort. Prompt public health response measures were initiated by Shanghai Customs and CDC authorities. CONCLUSIONS: This case demonstrates the feasibility and impact of rapid, genomically informed surveillance at the border for detecting and characterizing travel-associated enteric virus outbreaks. The findings underscore the need for robust port-of-entry monitoring, rapid diagnostics, and integrated genomic analysis to mitigate transmission in group travel settings.