Answer: The stomach flu is viral gastroenteritis
The stomach flu is actually viral gastroenteritis. Gastroenteritis1 is the inflammation of the stomach and intestines that causes vomiting and diarrhea. When we refer to the "stomach flu", we are talking about gastroenteritis that is caused by an assortment of different viruses including norovirus and rotavirus. The “stomach flu” is not really a flu at all and has no relation to the influenza viruses. The annual flu shot does not protect you from the stomach flu. Viral gastroenteritis is commonly referred to as "stomach flu", "stomach virus", "stomach bug", "24 hour bug", or "winter vomiting disease". There are other causes of gastroenteritis including bacterial and parasitic infections. Food poisoning can also cause gastroenteritis. This website discusses all of these causes so you can learn to avoid them.
--Annie Pryor, Ph.D.