Gastroenteritis is inflammation of the lining of the stomach and small and large intestines. It is usually caused by infection with a microorganism but can also be caused by ingestion of chemical toxins or drugs.

• The infection is usually caused by an infection but can be caused by ingesting toxins or drugs.
• Typically, people have diarrhea, nausea, vomiting, and abdominal pain.
• The diagnosis is based on some laboratory tests and a person's history of recent contact with contaminated people, food, or water or antibiotic use.
• Thoroughly washing the hands after a bowel movement or contact with fecal matter is the best way to prevent infection.
• Antibiotics are used to eliminate only certain kinds of bacteria.

Gastroenteritis usually consists of mild to severe diarrhea that may be accompanied by loss of appetite, nausea, vomiting, cramps, and discomfort in the abdomen. Although gastroenteritis usually is not serious in a healthy adult, causing only discomfort and inconvenience, it can cause life-threatening dehydration (see Water Balance: Dehydration) and electrolyte imbalance (see Minerals and Electrolytes: Electrolytes) in the very ill or weak, the very young, and the very old. About 3 to 6 million children around the world die each year from infectious gastroenteritis.

Causes

Infections that cause gastroenteritis can be transmitted from person to person, especially if people with diarrhea do not thoroughly wash their hands after a bowel movement. Infection also can occur if people touch their mouth after touching an object (such as a diaper or toy) contaminated by infected stool. All such transmission involving infected stool is termed “fecal-oral transmission.” A person, and sometimes large numbers of people (in which case an outbreak of illness is called an epidemic), can also become infected by eating food or drinking water that has been contaminated by infected stool. Most foods can be contaminated with bacteria and cause gastroenteritis if not cooked thoroughly or pasteurized. Contaminated water is sometimes ingested in unexpected ways, such as when swimming in a pond contaminated by stool from an animal or in a swimming pool contaminated by stool from another person. In some cases, gastroenteritis is acquired through contact with animals that carry the infectious microorganism.

Infectious gastroenteritis may be caused by viruses, bacteria, or parasites. Chemical toxins and drugs can also cause gastroenteritis.

Viruses: Viruses are the most common cause of gastroenteritis in the United States. Certain viruses infect cells in the lining of the small intestine where they multiply and cause watery diarrhea, vomiting, and fever. Four categories of viruses cause most gastroenteritis: rotavirus, calicivirus (predominantly the norovirus), and less commonly, astrovirus, and enteric (intestinal) adenovirus.

Rotavirus (see Viral Infections) is the most common cause of severe, dehydrating diarrhea in young children. It usually affects those between the ages of 3 months and 15 months. Rotavirus is highly contagious. Most infections are spread by fecal-oral transmission. Adults may be infected after close contact with an infected infant, but the illness is generally mild. During the winter in temperate climates, rotavirus causes most cases of diarrhea that are serious enough to send infants and toddlers to the hospital. Each year in the United States, a wave of rotavirus illness begins in the Southwest in November and ends in the Northeast in March.

Norovirus most commonly infects older children and adults. Infections occur year-round. Most people are infected after swallowing contaminated food or water. Because norovirus is highly contagious, infection can easily be spread from person to person.

Astrovirus can infect people of all ages but usually infects infants and young children. Infection is most common in the winter and is spread by fecal-oral transmission.

Adenovirus most commonly affects children under the age of 2. Infections occur year-round and increase slightly in the summer. The infection is spread by fecal-oral transmission.

Other viruses (such as cytomegalovirus and enterovirus) can cause gastroenteritis in people who have an impaired immune system.

Did You Know... Worldwide, about 3 to 6 million children die each year from gastroenteritis caused by an infection.

Bacteria: Bacterial gastroenteritis is less common than viral gastroenteritis.

Some bacteria (such as certain strains of Escherichia coli [E. coli], Campylobacter, Shigella, and Salmonella) invade the lining of the small intestine or colon. There, they damage cells, causing tiny sores (ulcerations) that bleed, and allow a considerable leakage of fluid containing proteins, electrolytes, and water. The diarrhea contains white and red blood cells and sometimes visible blood.

Salmonella and Campylobacter are the most common bacterial causes of diarrhea in the United States. Both infections are most frequently acquired from undercooked poultry. Unpasteurized milk is also a possible source. Campylobacter is occasionally transmitted by dogs or cats with diarrhea. Salmonella can be transmitted by undercooked eggs and by having contact with reptiles (such as turtles or lizards).

Species of Shigella are the third most common bacterial cause of diarrhea in the United States and are usually transmitted person to person, although food-borne epidemics occur.

Several different subtypes of E. coli cause diarrhea. Enterohemorrhagic E. coli is the most significant subtype of E. coli in the United States and causes hemorrhagic colitis (see Gastroenteritis: Hemorrhagic Colitis) and sometimes hemolytic-uremic syndrome (see Bleeding and Clotting Disorders: Causes). The strain E. coli O157:H7 is the most common strain of this subtype in the US. Undercooked ground beef, unpasteurized milk and juice, and contaminated water are possible sources. Person-to-person transmission is common in day care centers. Another subtype of E. coli produces two toxins that cause watery diarrhea. This subtype is the most common cause of traveler's diarrhea (see Gastroenteritis: Traveler's Diarrhea). A third subtype of E. coli also causes watery diarrhea. It was once a common cause of diarrhea outbreaks in nurseries but is now rare. A fourth subtype of E. coli causes bloody or nonbloody diarrhea, primarily in developing countries. It is rare in the United States.

Other bacteria (such as Staphylococcus aureus, Bacillus cereus, and Clostridium perfringens) produce a toxin that can be present in contaminated food. The toxin can cause gastroenteritis without causing a bacterial infection. These toxins generally cause severe nausea, vomiting, and diarrhea. Symptoms begin within 12 hours of ingestion of contaminated food and lessen within 36 hours.

Several other bacteria cause gastroenteritis, but most are rare in the United States. Yersinia enterocolitica can cause gastroenteritis or a syndrome that mimics appendicitis. A person is infected after ingesting undercooked pork, unpasteurized milk, or contaminated water. Several Vibrio species (such as Vibrio parahaemolyticus) cause diarrhea after ingestion of undercooked seafood. Vibrio cholerae, which is responsible for the watery diarrhea that is the main symptom of cholera, sometimes causes severe dehydrating diarrhea in developing countries. Listeria causes food-borne gastroenteritis. Aeromonas is acquired from swimming in or drinking contaminated fresh water or briny, salty water. Plesiomonas shigelloides can cause diarrhea in people who have eaten raw shellfish or traveled to tropical regions in developing countries.

Parasites: Certain intestinal parasites, particularly Giardia lamblia, stick to or invade the lining of the intestine and cause nausea, vomiting, diarrhea, and a general sick feeling. The resulting infection, called giardiasis, is more common in cold climates but occurs in every region of the United States and throughout the world. If the disease becomes persistent (chronic), it can keep the body from absorbing nutrients, a condition known as a malabsorption syndrome. Infection is usually spread through person-to-person contact (often in day care centers) or from contaminated water.

Another intestinal parasite, called Cryptosporidium parvum, causes watery diarrhea that is sometimes accompanied by abdominal cramps, nausea, and vomiting. The resulting infection, called cryptosporidiosis, is usually mild in otherwise healthy people, but it may be severe or even fatal in people with a weakened immune system. It is most commonly acquired by drinking contaminated water.

Other parasites that can produce symptoms similar to those of cryptosporidiosis include Cyclospora cayetanensis and, in people with an impaired immune system, Isospora belli and a collection of organisms referred to as microsporidia. Entamoeba histolytica causes amebiasis, an infection of the large intestine and sometimes the liver and other organs. Amebiasis is a common cause of bloody diarrhea in developing countries and occasionally occurs in the United States.

Chemical Gastroenteritis: Gastroenteritis may result from ingesting chemical toxins. These toxins are usually produced by a plant, such as poisonous mushrooms, or by certain kinds of exotic seafood and thus are not the product of an infection. Gastroenteritis due to chemical toxicity can also occur after ingesting water or food contaminated by chemicals such as arsenic, lead, mercury, or cadmium. Heavy-metal poisoning frequently causes nausea, vomiting, abdominal pain, and diarrhea. Eating large amounts of acidic foods, such as citrus fruits and tomatoes, gives some people gastroenteritis.

Microorganisms That Cause Gastroenteritis Microorganism Common Sources Symptoms Antimicrobial Use Campylobacter Eating contaminated meat (especially undercooked poultry); drinking contaminated water or unpasteurized milk Often bloody, sometimes watery diarrhea lasting 1 day to a week or more Antibiotics given in the early stages of illness may shorten the duration of symptoms (for example, azithromycin, ciprofloxacin) Salmonella Eating contaminated food; contact with reptiles (iguanas, snakes, turtles) High fever, exhaustion, abdominal cramps, nausea, vomiting, diarrhea that may or may not be bloody. Symptoms usually last 3 to 7 days Antibiotics usually not given Shigella Person-to-person contact, especially in day care centers May be mild or severe. In mild cases, watery, loose stools. In severe cases, high fever, exhaustion, severe abdominal cramps, painful passage of stool containing blood and mucus. Symptoms usually last about a week without treatment Antibiotics shorten the duration of the illness and decrease chance of spread to another person (for example, ciprofloxacin, trimethoprim-sulfamethoxazole) Enterohemorrhagic Escherichia coli O157:H7 Eating undercooked ground beef or drinking unpasteurized milk or juice; swimming in contaminated pools; person-to-person contact; touching infected animals and then putting fingers in one's mouth Sudden abdominal cramps, watery diarrhea that usually becomes bloody within 24 hours, hemolytic-uremic syndrome Antibiotics not given Clostridium difficile Usually due to bacterial overgrowth in people who have been taking antibiotics Diarrhea Antibiotic use is stopped. In some cases, metronidazole is given by mouth Entamoeba histolytica Eating or drinking contaminated food or water Bloody diarrhea, abdominal pain, weight loss lasting 1 to 3 weeks. Can cause infection in liver and other organs Antiparasitic drugs given (for example, metronidazole, iodoquinol, paromomycin) Enterotoxigenic Escherichia coli (causes traveler's diarrhea) Eating or drinking contaminated food or water Frequent watery diarrhea. Usually lasts 3 to 5 days Antibiotics (for example, ciprofloxacin, levofloxacin) may help shorten duration of illness; azithromycin is given to children Vibrio cholerae Eating or drinking contaminated food or water Painless, watery diarrhea; vomiting. Can lead to massive fluid loss, shock Antibiotics given (for example, ciprofloxacin, doxycycline) Other types of Vibrio Shellfish Watery diarrhea, often with little nausea or vomiting Antibiotics given (for example, ciprofloxacin, doxycycline, trimethoprim-sulfamethoxazole) Staphylococcus aureus Bacillus cereus Clostridium perfringens Eating food contaminated by toxins produced by bacteria Severe nausea, vomiting, and diarrhea. Symptoms begin within 12 hours after eating contaminated food and lessen within 36 hours Antibiotics not given Rotavirus Epidemic and often seasonal Frequent watery diarrhea; vomiting and fever higher than 102. Symptoms begin 1 to 3 days after infection. May last 5 to 7 days Antibiotics and antiviral drugs not given Vaccine available for infants Norovirus Epidemic and often seasonal Frequent watery diarrhea; vomiting occurs in 90% of people; stomach cramps; headache; aches and pains; fever higher than 102° F (about 39° C) occurs in about 30%. Diarrhea usually affects adults. Symptoms begin 1 to 2 days after infection. Usually lasts 2 to 7 days. Antibiotics and antiviral drugs not given Astrovirus Epidemic and often seasonal Milder watery diarrhea; vomiting and fever. Symptoms begin 3 to 4 days after infection. Usually lasts 2 to 7 days. Similar to rotavirus Antibiotics and antiviral drugs not given Intestinal adenovirus Epidemic and often seasonal Frequent watery diarrhea lasts 1 to 2 weeks; mild vomiting begins 1 to 2 days after diarrhea; fever affects 50% of people. Symptoms begin 3 to 10 days after infection. Usually lasts 10 days or more Antibiotics and antiviral drugs not given Giardia Drinking contaminated stream water; person-to-person contact, particularly in day care centers Diarrhea, nausea, loss of appetite. More long-term illness (lasting several days to several weeks) may occur, with greasy stools, abdominal bloating, gas, fatigue, and weight loss Antiparasitic drugs given (for example, metronidazole or nitazoxanide) Cryptosporidium Drinking contaminated water; person-to-person contact. People with AIDS are particularly susceptible Watery diarrhea, crampy abdominal pain, nausea, fatigue, vomiting. Usually lasts about 2 weeks Antiparasitic drugs sometimes given (for example, nitazoxanide)

Gastroenteritis as a Side Effect of Drugs Nausea, vomiting, and diarrhea are common side effects of many drugs. Common culprits include antacids containing magnesium as a major ingredient, antibiotics, chemotherapy drugs, radiation therapy, colchicine (for gout), digoxin (usually used for heart failure or certain irregular heart rhythms), drugs used to remove or destroy internal parasitic worms, and laxatives. Laxative abuse can lead to weakness, vomiting, diarrhea, electrolyte loss, and other disturbances. Antibiotic use may cause Clostridium difficile-induced diarrhea. Recognizing that a drug is causing gastroenteritis can be difficult. In mild cases, a doctor can have a person stop taking the drug and later start taking it again. If the symptoms subside when the person stops taking the drug and resume when the person starts taking the drug again, then the drug may be the cause of the gastrointestinal symptoms. In severe cases of gastroenteritis, a doctor may instruct the person to stop taking the drug permanently.

Symptoms

The type and severity of the symptoms depend on the type and quantity of microorganism or toxin ingested. Symptoms also vary according to the person's resistance. Symptoms often begin suddenly—sometimes dramatically—with a loss of appetite, nausea, or vomiting. Audible rumbling of the intestine and abdominal cramping may occur. Diarrhea is the most common symptom and may be accompanied by visible blood and mucus. Loops of intestine may be painfully swollen (distended) with gas. The person may have a fever, feel generally sick, and experience aching muscles and extreme exhaustion.

Severe vomiting and diarrhea can lead to marked dehydration (see Water Balance: Dehydration). Symptoms of dehydration include weakness, decreased frequency of urination, dry mouth, and, in infants, lack of tears when crying. Excessive vomiting or diarrhea can result in low levels of potassium in the blood (hypokalemia). Low blood pressure and a rapid heart rate can also develop. Low levels of sodium in the blood (hyponatremia) also may develop, particularly if the person replaces lost fluids by drinking fluids that contain little or no salt, such as water and tea. Water and electrolyte imbalances are potentially serious, especially in the young, the old, and people with chronic diseases. Shock and kidney failure can occur in severe cases.

Diagnosis

The diagnosis of gastroenteritis is usually obvious from the symptoms alone, but the cause often is not. Sometimes other family members or coworkers have recently been ill with similar symptoms. Other times, gastroenteritis can be traced to contaminated water or inadequately cooked, spoiled, or contaminated food, such as raw seafood or mayonnaise left out of the refrigerator too long. Recent travel, especially to certain foreign countries, and recent antibiotic use may give clues as well.

If the symptoms are severe or last for more than 48 hours, stool samples may be cultured and examined in a laboratory for white blood cells and bacteria, viruses, or parasites.

If the symptoms persist beyond a few days, a doctor may need to examine the large intestine with a colonoscope (a flexible viewing tube used to view the lower part of the digestive tract) to determine whether the person has a disease such as ulcerative colitis.

Prevention

A rotavirus vaccine given by mouth is now available that is safe and effective against most strains of rotavirus. This vaccine is now part of the recommended infant vaccination schedule and is given at 2, 4, and 6 mo of age (see Newborns and Infants: Vaccinating Infants and Children).

For infants, a simple and effective way to prevent gastroenteritis is breastfeeding. Caregivers should wash their hands thoroughly with soap and water after changing diapers, and diaper-changing areas should be disinfected with a freshly prepared solution of household bleach (¼ cup bleach diluted in 1 gallon of water). Children with diarrhea should be excluded from child care centers for the duration of their symptoms. Children infected with E. coli that causes bloody diarrhea or Shigella should also have two negative stool cultures before they are allowed to return to the center.

Because most infections that cause gastroenteritis are transmitted by person-to-person contact, particularly through direct or indirect contact with infected stool, good hand washing with soap and water after a bowel movement is the most effective means of prevention. To prevent food-borne infections, hands should be washed before touching food, knives and cutting boards used to cut raw meat should be washed before use with any other food, meat and eggs should be cooked thoroughly, and leftovers should be refrigerated promptly after cooking. Only pasteurized dairy products and pasteurized apple juice should be used. Travelers should try to avoid possibly contaminated food and drink.

Treatment

Usually the only treatment needed for gastroenteritis is getting bed rest and drinking an adequate amount of fluids. Even a person who is vomiting should drink as much as can be tolerated, taking small frequent sips. If vomiting or diarrhea is prolonged or the person becomes severely dehydrated, intravenous fluids and electrolytes may be needed. Because children can become dehydrated more quickly, they should be given fluids with the appropriate mix of salts and sugars. Any of the commercially available solutions designed to replace lost fluids and electrolytes (rehydration solutions) are satisfactory. Carbonated beverages, teas, sports drinks, beverages containing caffeine, and fruit juices are not appropriate. If the child is breastfed, breastfeeding should continue. Drugs that control severe vomiting are not generally given to young children. For adults, a doctor may give a drug, either as an injection or as a suppository, to control severe vomiting.

As the symptoms subside, the person may gradually add foods to the diet. Traditionally, bland foods such as cereal, gelatin, bananas, rice, applesauce, and toast are given, but there is no evidence that these are superior to other foods. If the diarrhea continues for 24 to 48 hours and there is no blood in the stool to indicate a more serious bacterial infection, the doctor may prescribe a drug to control the diarrhea, such as diphenoxylate, or instruct the person to use an over-the-counter drug, such as loperamide. Again, these drugs usually are not given to children under the age of 5.

Because antibiotics can cause diarrhea and may encourage the growth of organisms resistant to antibiotics, they are rarely appropriate, even when a known bacterium is causing gastroenteritis. Antibiotics may be used, however, when certain bacteria, such as Campylobacter, Shigella, and Vibrio, are the cause, and for people who have traveler's diarrhea.

Parasitic infections are treated with antiparasitic drugs such as metronidazole and nitazoxanide.

Some bacteria are naturally found in the body and promote the growth of good bacteria (probiotics). The use of probiotics, such as lactobacillus (normally found in the mouth, digestive tract, and vagina), is generally safe and may relieve symptoms. They can be given in the form of yogurt with active cultures.

Last full review/revision September 2007 by Thomas G. Boyce, MD, MPH