What causes Viral Gastroenteritis ?
Four types of viruses cause most cases of viral gastroenteritis.
                
Rotavirus
                
Rotavirus is the leading cause of gastroenteritis among infants and young children. Rotavirus infections are most common in infants 3 to 15 months old. Symptoms usually appear 1 to 3 days after exposure. Rotavirus typically causes vomiting and watery diarrhea for 3 to 7 days, along with fever and abdominal pain. Rotavirus can also infect adults who are in close contact with infected children, but the symptoms in adults are milder.
                
Caliciviruses
                
Caliciviruses cause infection in people of all ages. Norovirus is the most common calicivirus and the most common cause of viral gastroenteritis in adults. Norovirus is usually responsible for epidemics of viral gastroenteritis. Norovirus outbreaks occur all year but are more frequent from October to April. People infected with norovirus typically experience nausea, vomiting, diarrhea, abdominal cramps, fatigue, headache, and muscle aches. The symptoms usually appear 1 to 2 days after exposure to the virus and last for 1 to 3 days.
                
Adenovirus
                
Adenovirus mainly infects children younger than 2 years old. Of the 49 types of adenoviruses, one strain affects the gastrointestinal tract, causing vomiting and diarrhea. Symptoms typically appear 8 to 10 days after exposure and last 5 to 12 days. Adenovirus infections occur year-round.
                
Astrovirus
                
Astrovirus primarily infects infants and young children, but adults may also be infected. This virus causes vomiting and watery diarrhea. Symptoms usually appear 3 to 4 days after exposure and last 2 to 7 days. The symptoms are milder than the symptoms of norovirus or rotavirus infections. Infections occur year-round, but the virus is most active during the winter months.
                
Viral gastroenteritis is often mistakenly called stomach flu, but it is not caused by the influenza virus. Some forms of gastroenteritis are caused by bacteria or parasites rather than viruses. More information about bacterial infections is provided in the NIDDK health topic, Foodborne Illnesses fact sheet from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).