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Overview of Gastroenteritis


Jonathan Gotfried

, MD, Lewis Katz School of Medicine at Temple University

Reviewed/Revised Jun 2023
Topic Resources

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, medications, or drugs.

  • Gastroenteritis is usually caused by an infection.

  • 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.

  • Antibiotics are given to treat gastroenteritis that is caused only by parasites or certain bacteria.

  • 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.

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 Dehydration Dehydration is a deficiency of water in the body. Vomiting, diarrhea, excessive sweating, burns, kidney failure, and use of diuretics may cause dehydration. People feel thirsty, and as dehydration... read more and electrolyte imbalance Electrolyte Balance in the very ill or weak, the very young, and the very old.

Each year in the United States, about 48 million people develop gastroenteritis by eating contaminated food and about 3,000 die of it.

Each year worldwide, about 1.6 million people die of infectious gastroenteritis.

Causes of Gastroenteritis

The most common causes of gastroenteritis are

  • Viruses (most common)

  • Bacteria

  • Parasites

Other causes include

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 Overview of Viral Infections A virus is composed of nucleic acid, either DNA or RNA, surrounded by a protein coat. It requires a living cell in which to multiply. A viral infection can lead to a spectrum of symptoms from... read more 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 types of viruses cause gastroenteritis: norovirus, rotavirus, astrovirus, and enteric (intestinal) adenovirus.

Most viral gastroenteritis infections are caused by

Astrovirus can infect people of all ages but usually infects infants and young children. In temperate climates, infection is most common during winter months. In tropical climates, infection is more common during summer months. It is spread by fecal-oral transmission. Symptoms start 3 to 4 days after infection.

Adenovirus is the 4th most common cause of childhood viral gastroenteritis. It 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 and in respiratory droplets of moisture such as those produced by coughing. Anyone nearby may inhale these droplets and become infected. Symptoms start 3 to 10 days after infection.

Did You Know...

  • Worldwide, about 1.6 million people die each year of gastroenteritis caused by an infection.


The most common bacterial causes of gastroenteritis are

Certain species, such as Vibrio cholerae Cholera Cholera is a serious infection of the intestine that is caused by the gram-negative bacteria Vibrio cholerae and that causes severe diarrhea, which can be fatal without treatment. People... read more and enterotoxigenic strains of E. coli Bacteria Bacteria , attach 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 Escherichia coli Infections Escherichia coli (E. coli) are a group of gram-negative bacteria that normally reside in the intestine of healthy people, but some strains can cause infection in the digestive... read more , Campylobacter Campylobacter Infections Several species of the gram-negative bacteria Campylobacter (most commonly Campylobacter jejuni) can infect the digestive tract, often causing diarrhea. People can be infected... read more , Shigella Shigellosis Shigellosis is infection by the gram-negative bacteria Shigella. It results in watery diarrhea or dysentery (the frequent and often painful passage of small amounts of stool that contain... read more , Salmonella Salmonella Infections The gram-negative bacteria Salmonella typically cause diarrhea and sometimes cause a more serious infection, typhoid fever. People are usually infected when they eat contaminated food... read more , and Clostridioides difficile Overview of Clostridial Infections Clostridia are bacteria that commonly reside in the intestine of healthy adults and newborns. Clostridia also reside in animals, soil, and decaying vegetation. These bacteria produce spores... read more ) invade the lining of the small or large intestine (colon). There, they damage cells, causing sores (ulcerations) that bleed, and allow a considerable leakage of fluid containing proteins, electrolytes, and water. The diarrhea contains microscopic white and red blood cells and sometimes visible blood.

Salmonella and Campylobacter are 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 are also a 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.

Clostridioides difficile (C. diff) is now probably the most common bacterial cause of diarrhea in the United States and is the most common cause of diarrhea that occurs after treatment with antibiotics (see Drug-Related Gastroenteritis Drug-Related Gastroenteritis and Chemical-Related Gastroenteritis Gastroenteritis is inflammation of the lining of the stomach and small and large intestines. Although it is usually caused by infection with a microorganism, it can also be caused by ingesting... read more ). 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 Clostridioides difficile bacteria to grow in their place. Clostridioides difficile produces a toxin that causes watery diarrhea that ranges from mild to severe and bloody (see also Clostridioides difficile–induced diarrhea Clostridioides (formerly Clostridium) difficile–Induced Colitis Clostridioides difficile (C. difficile)–induced colitis is an inflammation of the large intestine (colon) that results in diarrhea. The inflammation is caused by toxin produced... read more ).

Several other bacteria cause gastroenteritis, but most are rare in the United States. Yersinia enterocolitica Plague and Other Yersinia Infections Plague is a severe infection caused by the gram-negative bacteria Yersinia pestis and often involving the lymph nodes and/or lungs. The bacteria are spread mainly by the rat flea. Depending... read more Plague and Other <i >Yersinia</i> Infections can cause gastroenteritis or a syndrome that mimics appendicitis. A person is infected after ingesting undercooked pork, unpasteurized milk, or contaminated water. Several Vibrio Cholera Cholera is a serious infection of the intestine that is caused by the gram-negative bacteria Vibrio cholerae and that causes severe diarrhea, which can be fatal without treatment. People... read more species (such as Vibrio parahaemolyticus) cause diarrhea after ingesting undercooked seafood. Vibrio cholerae, which causes cholera Cholera Cholera is a serious infection of the intestine that is caused by the gram-negative bacteria Vibrio cholerae and that causes severe diarrhea, which can be fatal without treatment. People... read more , is responsible for the watery diarrhea that sometimes causes severe dehydration in people in low-resource countries. Epidemics may occur after natural disasters or in refugee camps. Listeria Listeriosis Listeriosis is infection caused by the gram-positive bacteria Listeria monocytogenes, usually when contaminated food is eaten. People may consume the bacteria in contaminated dairy products... read more can rarely cause foodborne gastroenteritis but more often causes a bloodstream infection or meningitis in pregnant women, newborns, or older adults. 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 low-resource countries.


The most common parasites are

Certain intestinal parasites, particularly Giardia intestinalis, stick to the lining of the intestine and cause nausea, vomiting, diarrhea, and a general sick feeling. The resulting infection, called giardiasis Giardiasis Giardiasis is an infection of the small intestine caused by the single-celled protozoan parasite Giardia. The main symptoms are abdominal cramping and diarrhea. People may have abdominal... read more , occurs in every region of the United States and throughout the world. If the infection becomes persistent (chronic), it may keep the body from absorbing nutrients (called malabsorption syndrome Overview of Malabsorption Malabsorption syndrome refers to a number of disorders in which nutrients from food are not absorbed properly in the small intestine. Certain disorders, infections, and surgical procedures can... read more ). Infection is usually spread through drinking contaminated water (sometimes from wells or unconventional water sources encountered while hiking or camping), eating contaminated food, or through 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 Cryptosporidiosis Cryptosporidiosis is an intestinal infection caused by Cryptosporidium, a protozoan parasite. The main symptoms are abdominal cramping and diarrhea. People acquire the infection by consuming... read more 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, Cystoisospora belli and a collection of organisms referred to as microsporidia Microsporidiosis Microsporidiosis is infection caused by Microsporidia, which are parasitic fungi. Symptoms depend on the organs infected, but infections can cause diarrhea, other intestinal symptoms, or eye... read more . Entamoeba histolytica causes amebiasis Amebiasis Amebiasis is an infection of the large intestine and sometimes the liver and other organs that is caused by the single-celled protozoan parasite Entamoeba histolytica, an ameba. The amebas... read more , an infection of the large intestine and sometimes the liver and other organs. Amebiasis is a common cause of bloody diarrhea in countries where sanitation is inadequate but is rare in the United States.

Symptoms of Gastroenteritis

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. The abdomen (and the loops of intestine inside) may be painfully swollen (distended) with gas.

The person may have a fever, feel generally sick, and have aching muscles and extreme exhaustion.

Gastroenteritis caused by viruses

Adenovirus causes mild vomiting 1 to 2 days after diarrhea starts. The diarrhea can last 1 to 2 weeks. Infants and children may have mild vomiting that typically starts 1 to 2 days after diarrhea starts. A low fever occurs in about 50% of people. Some people may have nasal congestion, a runny nose, scratchy throat, and cough. Symptoms are typically mild but can last longer than with other viral causes of gastroenteritis.

Astrovirus symptoms are similar to a mild rotavirus infection.

Gastroenteritis caused by bacteria

Bacteria are likely to cause fever and may cause bloody or watery diarrhea. Some bacteria also cause vomiting.

Gastroenteritis caused by parasites

Parasites typically cause diarrhea that may last for a long time and may cause diarrhea that comes and goes. The diarrhea is usually not bloody. People may be very tired and lose weight when they have long-lasting diarrhea caused by a parasitic infection.

Complications of gastroenteritis

Severe vomiting and diarrhea can lead to marked fluid loss (dehydration Dehydration Dehydration is a deficiency of water in the body. Vomiting, diarrhea, excessive sweating, burns, kidney failure, and use of diuretics may cause dehydration. People feel thirsty, and as dehydration... read more ). 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 electrolyte problems Overview of Electrolytes More than half of a person's body weight is water. Doctors think about water in the body as being restricted to various spaces, called fluid compartments. The three main compartments are Fluid... read more such as low levels of potassium in the blood Hypokalemia (Low Level of Potassium in the Blood) In hypokalemia, the level of potassium in blood is too low. A low potassium level has many causes but usually results from vomiting, diarrhea, adrenal gland disorders, or use of diuretics. A... read more (hypokalemia) and dehydration, which can cause low blood pressure and a rapid heart rate. Low levels of sodium in the blood Hyponatremia (Low Level of Sodium in the Blood) In hyponatremia, the level of sodium in blood is too low. A low sodium level has many causes, including consumption of too many fluids, kidney failure, heart failure, cirrhosis, and use of diuretics... read more (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. Low blood volume (hypovolemic shock Hypovolemic shock Shock is a life-threatening condition in which blood flow to the organs is low, decreasing delivery of oxygen and thus causing organ damage and sometimes death. Blood pressure is usually low... read more ) and kidney failure can occur in severe cases.

Diagnosis of Gastroenteritis

  • A doctor's evaluation

  • History of contact with ill people, certain animals, or contaminated food or water; recent travel; or antibiotic use

  • Sometimes stool tests

The diagnosis of gastroenteritis is usually obvious from the symptoms alone, but doctors consider other gastrointestinal disorders that cause similar symptoms (for example, ulcerative colitis Ulcerative Colitis Ulcerative colitis is a chronic inflammatory bowel disease in which the large intestine (colon) becomes inflamed and ulcerated (pitted or eroded), leading to flare-ups (bouts or attacks) of... read more ).

The cause of gastroenteritis often is not obvious and needs to be sought. Sometimes other family members or coworkers have recently been ill with similar symptoms, or people have had contact with certain animals. 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.

Seriously ill people may need blood tests to determine whether they have water and electrolyte imbalances or tests to determine how their kidneys are functioning.

Treatment of Gastroenteritis

  • Fluids and rehydration solutions

  • Sometimes medications


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 Treatment Dehydration is loss of water from the body, usually caused by vomiting and/or diarrhea. Dehydration occurs when there is significant loss of body water and, to varying amounts, electrolytes... read more ) are satisfactory. Carbonated beverages, teas, sports drinks, beverages containing caffeine, and fruit juices are not appropriate. If the child is breastfed, breastfeeding Breastfeeding Breast milk is the ideal food for newborns and infants. Although babies may be fed breast milk or formula, the World Health Organization (WHO) and American Academy of Pediatrics (AAP) recommend... read more Breastfeeding should continue.

As the symptoms subside, the person may gradually add foods to the diet. Although often recommended, 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 adults antinausea medications, such as ondansetron, prochlorperazine, and promethazine, by mouth or as an injection or suppository. Children who are still vomiting after 24 hours need to be seen again by a doctor.

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 medication to control the diarrhea, such as diphenoxylate, or instruct the person to use an over-the-counter medication, such as loperamide. These medications (called antidiarrheal medications) are not given to children under 18 years of age with acute diarrhea. Antidiarrheal medications are also not given to people who have recently used antibiotics, who have bloody diarrhea, who have small amounts of blood in the stool that are too small to be seen, or who have diarrhea and fever.

Because antibiotics can cause diarrhea and may encourage the growth of organisms resistant to antibiotics, they are usually best avoided, 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 Treatment Traveler’s diarrhea is an infection characterized by diarrhea, nausea, and vomiting that commonly occur in travelers to areas of the world with poor water purification. Traveler's diarrhea can... read more . Antibiotics are also used to treat diarrhea caused by Clostridioides difficile. The antibiotic that is used for treatment is different from the antibiotic that caused the Clostridioides difficile infection. (See also table .)

Did You Know...

  • Antibiotics do not always help diarrhea that is caused by bacteria.

Parasitic infections are treated with antiparasitic medications such as metronidazole, tinidazole, 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, there is insufficient evidence that probiotics prevent more serious consequences of gastroenteritis, such as the need for intravenous fluids or for hospitalization, to support their routine use to treat or prevent infectious diarrhea.

Prevention of Gastroenteritis

  • Vaccination

  • Handwashing

  • Breastfeeding

Caregivers should wash their hands thoroughly with soap and water before preparing bottles for formula-fed infants. If soap and clean water are unavailable, an antibacterial hand sanitizer should be used.

Caregivers 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 tests before they are allowed to return to the center.

Did You Know...

  • It takes 20 seconds to receive the full benefit of handwashing with regular soap and water.

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 handwashing 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 Clostridioides 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).

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