Genomic insight into a festival-linked foodborne outbreak caused by enterotoxigenic <i>Staphylococcus aureus</i> ST1-t321 in the Republic of Korea

Objectives: This study investigated a large-scale foodborne outbreak caused by Staphylococcus aureus during a local festival in the Republic of Korea and performed genomic and molecular epidemiological analyses using whole-genome sequencing (WGS). Methods: Microbiological identification was performed using clinical, food, and environmental samples. Molecular characterization included pulsed-field gel electrophoresis (PFGE), multilocus sequence typing, and spa typing. WGS was conducted to evaluate clonal relatedness, virulence factors, and antimicrobial resistance genes. Results: A total of 141 suspected cases and 18 laboratory-confirmed cases were identified, and 24 S. aureus isolates were recovered (18 from patients, 3 from food samples, and 3 from environmental samples). All 17 isolates included in the genomic analysis carried the sea and sec genes and belonged to ST1-t321, with pairwise differences of 8-33 SNPs, supporting a clonal origin. These isolates exhibited a previously unreported PFGE pattern (STAS16.170) in the Republic of Korea. Virulence profiling identified hemolysin genes (hlgA, hlgB, hlgC), leukocidin genes (lukD, lukE), and immune evasion genes (sak, scn). In addition, all isolates were methicillin-susceptible and lacked mecA and mecC. Conclusion: This large-scale foodborne outbreak demonstrated that a single contaminated food source can result in widespread illness during mass gatherings. Genomic analysis clarified the clonal relatedness of the outbreak strains and highlighted the value of genomic surveillance for the early detection and prevention of S. aureus outbreaks.