24 Hour Stomach Bug 2025. The stomach flu (norovirus) is an acute form of gastroenteritis, or inflamed stomach or intestinal lining caused by a virus, bacteria or parasite. What norovirus isn't, however, is the stomach flu — despite what you might read or hear to the contrary.

Norovirus is a leading cause of acute gastroenteritis, or an inflammation of the lining of the stomach and intestines, per the cdc. It takes your body several days at the least to mount a defense against viruses and bacteria.