An infection or irritation of the stomach and intestines, which may be caused by viruses or by bacteria or parasites from spoiled food or unclean water. Other causes include eating food that irritates the stomach lining and emotional upsets such as anger, fear, or stress. Symptoms include diarrhea, nausea, vomiting, and abdominal cramping. Some causes of gastroenteritis:

• bacteria
• escherichia coli
• salmonella
• shigella

• viruses
• norwalk virus
• rotavirus

• parasites
• cryptosporidia
• entamoeba histolytica
• giardia lamblia.