A medical student after finishing his final year exams went on a cruise ship to Singapore. While on the ship he had sea food including shellfish such as clams and oysters. After 2 days, he developed fever, nausea, vomiting and diarrhoea. What is the causative agent?

The clinical scenario describes a case of norwalk infection. The most common cause of diarrhea in older children and adults is the Norwalk virus (Norovirus). They occur in group settings such as banquet halls, cruise ships, dormitories, and campgrounds, where outbreak sources are usually contaminated food and/or water. Potential sources of contaminated food include shellfish such as clams and oysters, which are contaminated by water at source. Clinical features are nausea, vomiting, watery diarrhea, abdominal pain. A person usually develops symptoms of gastroenteritis 12 to 48 hours after being exposed to norovirus. Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition