Viruses are a leading cause of foodborne illness. They can contaminate food and water and be transferred from people to food or surfaces. While viruses cannot grow on food, they can grow inside a person's intestines once ingested. Hepatitis A and Norovirus are two major foodborne illnesses caused by viruses. They are commonly associated with ready-to-eat foods and shellfish from contaminated water. Prevention focuses on handwashing and keeping infected employees out of food operations.