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Overview of Gastroenteritis

by Thomas G. Boyce, MD, MPH

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.

  • Gastroenteritis 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 a person’s history of recent contact with contaminated food, water, or people infected with certain microorganisms; recent use of antibiotics; and sometimes laboratory tests.

  • Thoroughly washing the hands after a bowel movement or contact with fecal matter and avoidance of undercooked foods are the best ways to prevent infection.

  • Antibiotics are used to treat only certain kinds of bacteria that cause gastroenteritis.

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 Dehydration) and electrolyte imbalance (see Electrolyte Balance) in the very ill or weak, the very young, and the very old. Each year in the United States, about 1 in 6 people develops gastroenteritis by eating contaminated food. About 1.5 million children around the world die each year from infectious gastroenteritis (see Gastroenteritis in Children).


The most common causes of gastroenteritis are

  • Viruses (most common)

  • Bacteria

  • Parasites

Other causes include

  • Chemical toxins

  • Drugs

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 direct contact with animals that carry the infectious microorganism.


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 in Infants and Children) is the most common cause of severe, dehydrating diarrhea among young children worldwide. Its incidence in the United States has decreased by 80% since rotavirus vaccines were added to the routine vaccination schedule. 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. It is now the most common cause of gastroenteritis in the United States. Infections occur year-round, but 80% occur from November to April. Most people are infected after swallowing contaminated food or water. Because norovirus is highly contagious, infection can easily be spread from person to person. This virus causes most cases of gastroenteritis epidemics on cruise ships and in nursing homes.

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 1.5 million children die each year from gastroenteritis caused by an infection.


Bacterial gastroenteritis is less common than viral gastroenteritis. Bacteria cause gastroenteritis by various means. Certain species, such as Vibrio cholerae , and enterotoxigenic strains of Escherichia coli( E. coli) and Clostridium difficileattach to the lining of the intestines without invading and produce enterotoxins. These toxins cause the intestines to secrete water and electrolytes, resulting in watery diarrhea.

Some bacteria (such as certain strains of 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 eating undercooked poultry. Unpasteurized milk is also a possible source. Campylobacter is occasionally transmitted by dogs or cats with diarrhea. Salmonella can be transmitted by eating undercooked eggs and by having contact with reptiles (such as turtles or lizards), birds, or amphibians (such as frogs and salamanders).

Species of Shigella (see Shigellosis) are the third most common bacterial cause of diarrhea in the United States and are usually transmitted person to person (especially in day care centers), although foodborne outbreaks occur.

Clostridium difficile is the most common cause of diarrhea that occurs after treatment with antibiotics (see Gastroenteritis as a Side Effect of Drugs). However, it sometimes occurs in people who have not been treated with antibiotics. Antibiotics kill the healthy bacteria that normally reside in the intestines, which allows Clostridium difficilebacteria to grow in their place. Clostridium difficile produces a toxin that causes severe watery diarrhea.

Several different subtypes of E. coli cause diarrhea. Enterohemorrhagic E. coli (also called Shiga toxin-producing E. coli) is the most significant subtype of E. coli in the United States and causes hemorrhagic colitis (see Hemorrhagic Colitis) and hemolytic-uremic syndrome (see Thrombocytopenia (ITP, TTP)) in about 5% of people. E. coli O157:H7 is the most common strain of this subtype in the United States. Undercooked ground beef, unpasteurized milk and juice, and contaminated water are possible sources. Person-to-person transmission is common in day care centers. Outbreaks have occurred among people who have gone swimming in pools or lakes or at water parks (called recreational water illness―see What Are Recreational Water Illnesses (RWIs)? ). Another subtype of E. coli(called enterotoxigenic E. coli ) produces two toxins that cause watery diarrhea. This subtype is the most common cause of traveler’s diarrhea (see Traveler’s Diarrhea) in people visiting developing countries. 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. colicauses 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 ingesting 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 ingesting undercooked seafood. Vibrio cholerae , which is responsible for the watery diarrhea that is the main symptom of cholera (see Cholera), sometimes causes severe dehydrating diarrhea in developing countries. Epidemics may occur after natural disasters or in refugee camps. Listeria (see Listeriosis) causes foodborne 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.


Certain intestinal parasites, particularly Giardia intestinalis , stick to or invade the lining of the intestine and cause nausea, vomiting, diarrhea, and a general sick feeling. The resulting infection, called giardiasis (see 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 (see Overview of Malabsorption). Infection is usually spread through drinking contaminated water (sometimes from wells or unconventional water sources encountered while hiking or camping) or, less commonly, via person-to-person contact (such as in day care centers).

Another intestinal parasite, called Cryptosporidium parvum , causes watery diarrhea that is sometimes accompanied by abdominal cramps, nausea, and vomiting. The resulting infection, called cryptosporidiosis (see 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. Because it is resistant to usual concentrations of chlorine, this parasite is the most common cause of recreational water illness in the United States.

Other parasites that can cause 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 (see Amebiasis). Amebiasis is a common cause of bloody diarrhea in developing countries but is rare in the United States.

Chemical gastroenteritis

Gastroenteritis may result from ingesting chemical toxins (see Chemical Food Poisoning). 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


Common Sources


Antimicrobial Use


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 or ciprofloxacin).


Eating contaminated food

Contact with reptiles (for instance, iguanas, snakes, and turtles), birds, or amphibians (for instance, frogs and salamanders)

High fever, exhaustion, abdominal cramps, nausea, vomiting, diarrhea that may or may not be bloody

Symptoms usually last 3 to 7 days

Antibiotics usually are not given.


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 or trimethoprim-sulfamethoxazole).

Enterohemorrhagic Escherichia coli(most commonly E. coli O157:H7―see Hemorrhagic Colitis)

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 the mouth

Sudden abdominal cramps, watery diarrhea that usually becomes bloody within 1 to 3 days, and hemolytic-uremic syndrome in about 5% of people

Antibiotics are not given because they increase the risk of developing hemolytic-uremic syndrome.

Clostridium difficile

Usually due to bacterial overgrowth in people who have been taking antibiotics


Antibiotic that caused the illness is stopped.

Metronidazole, vancomycin, or fidaxomicin 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 are given (for example, metronidazole, iodoquinol, or 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 or levofloxacin) may help shorten duration of illness.

Azithromycin is given to children.

Vibrio cholerae

Eating or drinking contaminated food or water

Painless, watery diarrhea and vomiting

Can lead to massive fluid loss and shock

Antibiotics are given (for example, ciprofloxacin or doxycycline).

Other types of Vibrio


Watery diarrhea, often with little nausea or vomiting

Antibiotics are given (for example, ciprofloxacin, doxycycline, or 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 are not given.


Epidemic and often seasonal

Frequent watery diarrhea

Vomiting and fever higher than 102° F (about 39°C)

Symptoms begin 1 to 3 days after infection

May last 5 to 7 days

Antibiotics and antiviral drugs are not given.

Vaccines are available for infants.


Epidemic and often seasonal

Frequent watery diarrhea

Vomiting, especially in children

Stomach cramps, headache, and aches and pains

Fever higher than 102° F (about 39°C) occurs in about 30% of people

Diarrhea usually affects adults

Symptoms begin 1 to 2 days after infection

Usually lasts 2 to 7 days

Antibiotics and antiviral drugs are not given.


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 are 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 are not given.


Drinking contaminated water

Person-to-person contact, particularly in day care centers

Diarrhea, nausea, and 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 are given (for example, metronidazole or nitazoxanide).


Drinking contaminated water

Person-to-person contact

Recreational water exposure

People with impaired immune systems are particularly susceptible

Watery diarrhea, crampy abdominal pain, nausea, fatigue, and vomiting

Usually lasts about 2 weeks

Antiparasitic drugs are sometimes given (for example, nitazoxanide).


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 have aching muscles and extreme exhaustion.

Severe vomiting and diarrhea can lead to marked dehydration (see 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—see Hypokalemia (Low Level of Potassium in the Blood)). Low blood pressure and a rapid heart rate can also develop. Low levels of sodium in the blood (hyponatremia—see Hyponatremia (Low Level of Sodium in the Blood)) 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.


  • A doctor's evaluation

  • History of contact with contaminated food or water or recent travel or antibiotic use

  • Sometimes stool tests

  • Sometimes sigmoidoscopy

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 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 sigmoidoscope (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.


Two rotavirus vaccines given by mouth are available and are safe and effective against most strains of rotavirus. Rotavirus vaccination is part of the recommended infant vaccination schedule (see Figure: Vaccinating Infants and Children).

For infants, a simple and effective way to help prevent gastroenteritis is breastfeeding. Caregivers should wash their hands thoroughly with soap and water before preparing bottles for formula-fed infants. They should also wash their hands after changing diapers. 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 day 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.

Infants and other people with a weakened immune system should not be exposed to reptiles, birds, or amphibians, because these animals typically carry Salmonella bacteria, and infection is more severe in these groups of people.

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 foodborne 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 high-risk foods and beverages, such as those sold by street vendors.

To prevent recreational water illness, people should not swim if they have diarrhea. Infants and toddlers should have frequent diaper checks and should be changed in a bathroom and not near the water. Swimmers should avoid swallowing water while swimming.

Because use of most antibiotics can increase the risk of diarrhea caused by Clostridium difficile infection, antibiotics are used only when necessary and never in situations in which they will have no effect (for example, for a viral infection).


  • Fluids and rehydration solutions

  • Sometimes drugs

  • Possibly probiotics


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, fluids and electrolytes given by vein (intravenously) 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 (called oral 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.

As the symptoms subside, the person may gradually add foods to the diet. There is no need to limit the diet to bland foods such as cereal, gelatin, bananas, rice, applesauce, and toast. However, some people are unable to tolerate milk products for a few days after having diarrhea.


A doctor may give antinausea drugs by mouth for mild to moderate vomiting. If vomiting is severe, antinausea drugs may be given as an injection or suppository. Certain antinausea drugs, such as ondansetron, are now safe for children age 2 and older.

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. These drugs usually are not given to children under the age of 2.

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. Antibiotics are also used to treat diarrhea caused by Clostridium difficile. The antibiotic that is used for treatment is different from the antibiotic that caused the Clostridium difficile infection.

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 (typically present in yogurt) may slightly shorten the duration of diarrhea (perhaps by less than a day). However, probiotics probably do not prevent more serious consequences of gastroenteritis, such as the need for intravenous fluids or for hospitalization.

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