Stomach viruses infect the tissues of the stomach or intestines, causing inflammation and other symptoms throughout the digestive system, according to Mayo Clinic. The most common viruses that cause these infections include norovirus and rotavirus, which are spread by contaminated food or water or those already infected with the virus.
Norovirus and rotavirus infections cause viral gastroenteritis, commonly referred to as the stomach flu, says Mayo Clinic. Symptoms of viral gastroenteritis include fever, nausea, vomiting, abdominal cramps and pain, and nonbloody diarrhea. Symptoms are similar to and are often confused with bacterial gastroenteritis, which is caused by a wide variety of bacteria such as E. coli.