Causes of Viral Gastroenteritis

The viruses that cause viral gastroenteritis damage the cells in the lining of the small intestine. As a result, fluids leak from the cells into the intestine and produce watery diarrhea. Four types of viruses cause most viral gastroenteritis.

• Rotavirus is the leading cause of gastroenteritis among children 3 to 15 months old. Most children have been exposed to the virus by age 2. Children with rotavirus have vomiting and watery diarrhea for 3 to 8 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. Symptoms of rotavirus infection appear 1 to 2 days after exposure. In the United States, rotavirus infections are most common from November to April.
  
  
• Adenovirus serotypes 40 and 41 cause gastroenteritis mainly in children younger than 2 years old. Infections occur all year round; vomiting and diarrhea appear approximately 1 week after exposure.
  
  
• Caliciviruses cause infection in persons of all ages. This family of viruses is further divided into the noroviruses (example, Norwalk virus) and the sapoviruses (example, Sapporo virus). Caliciviruses are transmitted from person to person and also through contaminated water or food--especially oysters from contaminated waters. The noroviruses are often responsible for epidemics of viral gastroenteritis. In addition to vomiting and diarrhea, people infected with caliciviruses may have muscle aches. The symptoms appear within 1 to 3 days of exposure.
  
  
• Astrovirus also infects primarily infants, young children, and the elderly. This virus is most active during the winter months. Vomiting and diarrhea appear within 1 to 3 days of exposure.
  
  

Viral gastroenteritis is often mistakenly called "stomach flu," but it is not caused by the influenza virus and it does not infect the stomach. Also, viral gastroenteritis is not caused by bacteria or parasites. For information about bacterial infections, please see the Bacteria and Foodborne Illness fact sheet from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

source: http://digestive.niddk.nih.gov/ddiseases/pubs/viralgastroenteritis/index.htm