What is norovirus? Noroviruses are a group of viruses (previously known as Norwalk-like viruses) that can cause gastroenteritis, an inflammation of the stomach and intestines. Norovirus is the leading cause of foodborne illness outbreaks in Minnesota. This infection is often mistakenly referred to as the “stomach flu”. Norovirus is not related to the flu (influenza), which is a common respirator..