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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?

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.

Gastroenteritis may be diagnosed by a physician during a physical examination that includes a medical history and list of medications. Patients are typically asked to describe the type and duration of symptoms experienced, such as diarrhea, nausea, vomiting and/or abdominal cramping. However, many people (particularly adults) do not consult a physician for mild cases of gastroenteritis.

Other information that patients may be asked to provide includes:

  • Foods consumed in the past few days
  • Recent travel, especially to foreign countries (which can result in a condition known as traveler’s diarrhea)
  • Changes in medications
  • Friends and/or family members who are experiencing similar symptoms
Physicians may examine the abdomen for the presence of tenderness or masses, which sometimes indicate the presence of another underlying condition, such as appendicitis (inflammation of the appendix) or cholecystitis (inflammation of the gallbladder).

There is no specific test to diagnose gastroenteritis. If patients have been experiencing symptoms for 48 hours or longer, physicians may request a stool sample, which will be examined in a laboratory under a microscope after being put in a culture medium to detect the presence of bacteria, parasites or other microorganisms that may be causing the illness. Gastroenteritis caused by a rotavirus infection can be diagnosed with a stool test. Most cases of viral gastroenteritis are not diagnosed because symptoms are usually mild and are not seen by a physician.

If symptoms last for longer than a few days, a physician may perform a colonoscopy (an examination of the inside of the colon). This test will help determine whether a condition other than gastroenteritis, such as ulcerative colitis (chronic inflammation of the colon that produces ulcers in its lining), is causing symptoms.

How is infectious gastroenteritis treated?

Treatment for gastroenteritis varies according to the type and severity of the illness. Most cases resolve on their own within several days. Mild cases may be treated by replacing fluids and electrolytes (chemicals needed for normal body function) to prevent dehydration. Increasing fluid intake is particularly important for children because they become dehydrated faster than adults. Diarrhea that is caused by medications (e.g., antacids, antibiotics) is treated by stopping the drug.

Tips for replacing fluids include:

  • Begin by drinking small amounts of clear liquids (4 or more ounces each hour) as tolerated. Soft drinks, tea, coffee, fruit juice and sports drinks should be avoided because they do not replace electrolytes appropriately.
  • Drink plenty of oral rehydration solutions (liquids with glucose and electrolytes designed to replace fluids lost due to diarrhea) if diarrhea is severe. This is especially important for children.
  • Take antidiarrheal medications to ease symptoms of diarrhea. However, these medications should be avoided by children and patients experiencing a high fever or blood in the stools. Also, these medications should not be taken more than three days unless directed by a physician.
After vomiting subsides, patients may start to gradually eat solid foods. Some diet tips include:
  • Eat foods that contain salt, such as crackers or pretzels, to replace lost sodium.
  • Eat foods such as oatmeal, white rice, applesauce and bananas to help slow down bowel movements.
  • Eat foods that are easy to digest, such as broth or chicken soup.
  • Do not eat or drink foods and beverages, such as chewing gum and apple juice, that contain sorbitol, a sugar alcohol that worsens diarrhea.
  • Limit intake of dairy products, fatty and greasy foods (e.g., pizza) and high-fiber foods (e.g., bran cereal, whole-grain breads) because they may worsen diarrhea.
Cases of gastroenteritis that cause severe dehydration may require hospitalization. Patients may receive fluids intravenously (through a vein). Patients may be given antidiarrheal medications to ease diarrhea or antiemetics to treat nausea and/or vomiting. Although antiemetics are not typically administered to children, research shows that one such drug may be effective in treating youngsters with gastroenteritis.

Patients are rarely given antibiotics to treat a bacterial infection. There are only a few types of gastroenteritis (such as shigellosis) that require antibiotic treatment. In fact, antibiotics can cause gastrointestinal infections in some people. Patients who have eaten foods contaminated with pesticides or other types of toxins may have their stomachs pumped (lavage) to remove the contents.

Researchers are also currently working to develop new treatments for gastroenteritis. For example, a molecule in coral has proven effective in fighting the virus that causes gastroenteritis, which may prove promising in the development of improved treatments.


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 1 July 2015