Investigators are checking the outlet's preparation area, storage temperatures and ingredient supply routes, and have taken samples from patients and food handlers for pathogen testing. Results typically take several days.

Kimbap is classified as a relatively high-risk item in summer. The longer rice, egg, fish cake and vegetables sit together at room temperature, the better the conditions for bacterial growth. Standard guidance is to eat within two hours of preparation and to refrigerate below 10 degrees Celsius.

Because the outlet is inside a hospital, the customer profile is also under review. Patients with weakened immunity and their carers can develop more severe symptoms at the same bacterial load, so authorities are tracking those affected.

Officials advised anyone who develops symptoms after eating at the same chain or nearby outlets to seek medical care even before the cause is identified. Clusters should be reported to the local public health centre.

Administrative penalties and preventive measures will follow the investigation's findings.