Gastroenteritis has many possible causes, including bacteria, such as Staphylococcus aureus, Salmonella, Shigella, Clostridium botulinum, Clostridium perfringens, Escherichia coli, Campylobacter, Aeromonas, and Yersinia; protozoans such as Giardia lamblia and Cryptosporidium; amoebae, especially Entamoeba histolytica; parasites, such as Ascaris, Enterobius, and Trichinella spiralis; viruses (may be responsible for traveler’s diarrhea), such as rotaviruses, noroviruses, adenoviruses, echoviruses, and coxsackieviruses; ingestion of toxins, such as poisonous plants and toadstools; drug reactions, for example, to antibiotics; enzyme deficiencies; and food allergens.

Chronic gastroenteritis may be the result of another GI disorder, such as ulcerative colitis. Diarrhea outbreaks in day-care facilities are typically due to viral gastroenteritis.

In most patients, the disorder resolves with no sequelae. However, persistent or untreated gastroenteritis can cause severe dehydration and loss of crucial electrolytes, which can lead to shock, vascular collapse, renal failure and, rarely, death. Typically, infants, elderly people, and debilitated patients are at greatest risk because of their immature or impaired immune systems.

Patient history commonly reveals the acute onset of diarrhea accompanied by abdominal pain and discomfort. The patient may complain of cramping, nausea, and vomiting. He or she may also report malaise, fatigue, anorexia, fever, abdominal distention, and rumbling in the lower abdomen. If diarrhea is severe, the patient may experience rectal burning, tenesmus, and bloody, mucoid stools.