Infectious Diarrhea

Infectious gastroenteritis

What is infectious gastroenteritis?

Infectious gastroenteritis refers to an inflammation of the stomach or intestine (especially the small intestine) that is due to an infectious organism. Although often causing sudden and sometimes violent upsets, the illness does not usually last longer than two or three days. Stomach flu, food poisoning, and traveler's diarrhea are names commonly given to infectious gastroenteritis.

The most common cause of infectious gastroenteritis is a viral infection. Other causes include bacteria and parasites. Infectious gastroenteritis can be spread person to person by fecal-oral contact or by the ingestion of contaminated food and water. Occasionally, gastroenteritis is caused by infection or an underlying disease in another part of the body. Infectious gastroenteritis is usually acute (rapid onset and short course), but certain parasites (such as Giardia) can cause chronic diarrhea. Cyclospora, a parasite, is associated with recent outbreaks attributed to imported berries.

How is it diagnosed?

History: The individual may report contact with infected people, recent mountain camping or travel abroad, drinking unpurified water, eating of raw meat, seafood, unpasteurized dairy products, or of unhygienic food preparation. Or, there may be no history of such exposure.

The individual's medical history is pertinent, as certain medications and underlying illnesses may predispose (make more susceptible) a person to infectious gastroenteritis.

Gastroenteritis is recognized by a set of common symptoms including nausea, vomiting, diarrhea, abdominal pain or cramps, and loss of appetite. The combination of symptoms usually appears suddenly and may be so mild that it causes little disruption to daily routine, or the attack may be severe and disabling.

Bloody diarrhea, fever, and tenesmus (pain on defecation) may be clues to a more serious condition (inflammatory enteritis) or systemic disease.

The definitive (without question) diagnosis of infectious gastroenteritis depends on the identification of the causative agent. Often, however, the isolation of the particular agent is not feasible or cost-effective. Therefore, the diagnosis may rest on symptoms, the epidemiologic setting (appearance of infectious disease attacking many people at the same time in the same geographical area), the individual's recent history, and by ruling out other causes.

Physical exam: The physical findings are nonspecific (not indicative of a particular disease). Bowel sounds may be hyperactive and there may be abdominal tenderness. Irritation of the perianal area or throat may be present due to repeated bouts of diarrhea and vomiting. The individual should be assessed for signs of dehydration, including dry mucous membranes, sunken eyes, decreased skin tension (turgor), lethargy, increased heart rate, and changes in blood pressure when individual changes position (orthostatic).

Tests: In infectious diarrhea, visual (gross) examination of the stool is the single most important test. If it contains blood or mucus, microscopic examination should be done to look for ova (eggs) and parasites. Since a single stool may not reveal parasites even when they are present, three fresh, separate stools should be tested if blood or mucus is found. When symptoms persist beyond three to four days, when there is fever or bloody diarrhea, or if the individual's immune system is deficient (immunocompromised), a culture should be done on the stool to isolate the infective organism.

How is infectious gastroenteritis treated?

Treatment of gastroenteritis depends upon the cause of the illness. Viral gastroenteritis is self-limited and is treated by resting the stomach and intestines, allowing the diarrhea to run its course. Enough fluids should be taken in to prevent dehydration, but solid food should not be eaten until symptoms subside. Antibiotics may be indicated for bacterial infections. Parasitic infections are more difficult to treat, although a number of effective anti-parasitic drugs are available. Anti-diarrheals may also be necessary.

Severe or prolonged vomiting and diarrhea are treated by replenishing fluids and electrolytes (vital body salts). In extreme cases, fluids may be given intravenously. When symptoms are severe or persist for longer than 72 hours, medical assistance is required.


Imodium (Loperamide)

What might complicate it?

Severe or prolonged diarrhea and vomiting may result in the loss of essential body fluids and nutrients causing dehydration, shock, and collapse. Incorrect diagnosis of the cause of gastroenteritis often results in ineffective therapy. When bacterial or parasitic infections are inadequately treated, the infection may spread to other areas of the body, especially the liver.

Prolonged infections lower the body's immunity (defense system) and may result in the establishment of secondary or opportunistic infections. Factors that can lower immunity include infection with other organisms such as human immunodeficiency virus (HIV), treatment with steroidal drugs, underlying conditions such as lymphoma, leukemia, generalized cancer (malignancy), and even fatigue. The presence of multiple infections in the body often makes definitive diagnosis of infectious gastroenteritis difficult. Simultaneous treatment for multiple infections can reduce the effectiveness of therapy on either or both infections.

Predicted outcome

The prognosis for most cases of gastroenteritis is very good. The symptoms of acute gastroenteritis usually subside within 48-72 hours without medical treatment. The prognosis for more severe or prolonged cases is dependent upon the cause and effectiveness of treatment. In cases involving extensive intestinal infection, unusual reactions to medicines, or ineffective therapy, the prognosis can be poor. Extreme loss of body fluid and electrolytes, without replacement, can lead to hypovolemic shock, coma or death.


A diagnosis of gastroenteritis is straightforward although pinpointing the cause may not be. When an infectious agent cannot be isolated from stools, the cause may be infectious, non-infectious or the manifestation of an infection outside of the gastrointestinal tract.

Appropriate specialists

Gastroenterologist, internist and infectious disease specialist.

Last updated 7 August 2011

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