Gastroenteritis is inflammation of the gastrointestinal tract, involving the stomach, intestines, or both; usually resulting in diarrhea, abdominal cramps, nausea and possibly vomiting. Gastroenteritis is frequently termed "stomach flu" or "gastric flu" because the most frequent cause of gastroenteritis is viral. However, this loose terminology confuses some people becauseinfluenza viruses (flu viruses) do not cause gastroenteritis.


Gastroenteritis also can be confusing to people because gastroenteritis itself is considered a disease, but gastroenteritis can also be considered a symptom of other diseases.


For example, a person who has the symptoms of gastroenteritis and eventually develops bloody diarrhea is usually not diagnosed with gastroenteritis, but with a specific disease such as shigellosis. Unfortunately, there are many specific diseases that manifest with symptoms of gastroenteritis, usually early in the disease process.


To complicate things even more, often confusion is generated when the term gastroenteritis is modified by words like "mild" or "severe." "Severe gastroenteritis" is a non-specific term that usually means different things to different investigators. The meaning is usually implied by the disease process that is being discussed.


For example, if the context of an article about a viral cause of gastroenteritis, it often means diarrhea that causes dehydration; while another article about a bacterial cause of gastroenteritis it may mean bloody diarrhea with fever.


The best way to sort out this non-specific terminology associated with gastroenteritis is for authors and health care practitioners to define what they mean by gastroenteritis and its modifying terms. While there may be disagreement about the terms, at least their meaning will be clear to the readers of individual articles.


Consequently, for this article, gastroenteritis will mean the short-term (lasting about 2 to 5 days and resolution, sometime over an additional few days) occurrence of symptoms that may include some or all of the following:

  • Non-bloody diarrhea.
  • Nausea.
  • Vomiting (occasional, less than 48 hours).
  • Abdominal cramping (intermittent, usually relieved by a bowel movement).


Other symptoms may develop such as a mild fever (about 100 F, 37.7 C), mild chills, occasionally a headache, and/or muscle aches, and a feeling of being tired. All of the above symptoms may develop into severe gastroenteritis which means for this article, dehydration, which may be life-threatening, especially in children.


People with symptoms of diarrhea, bloody diarrhea, nausea, or vomiting that lasts more than five days, and often may have additional symptoms of fever (greater than 101 F, 38.3 C), malaise, dehydration, and sepsis, for this article, will not be considered to have gastroenteritis. However, people with such problems will be considered to have symptoms of gastroenteritis that are related to a specific disease, for example, shigellosis.


Not all investigators will agree with this designation and consider bloody diarrhea, vomiting more than 48 hours, fever higher than 101 F (38.3 C), dehydration, and relatively constant abdominal pain as severe gastroenteritis. However, these symptoms are not frequently associated with gastroenteritis or stomach flu that does not run a limited course, and does not resolve without professional or medical treatment, and are more often associated with other specific diseases, most of which require medical care.


Most children and adults diagnosed with shigellosis, E. coli 0157:H7 infections, salmonellosis, and other diseases are usually not diagnosed as having severe gastroenteritis or severe stomach flu. Readers may wonder why then, should such pathogens be listed as causes of gastroenteritis. The answer is simple.


The pathogens are listed because in many people, the pathogens produce only symptoms of gastroenteritis and do not go on to develop worse symptoms, often because an otherwise healthy person self-limits the infection. Not to list them would not give an accurate summation of the causes of gastroenteritis.


The symptoms of gastroenteritis are:


  • diarrhea,
  • nausea, 
  • abdominal cramps,
  • vomiting.


Not all affected individuals will develop all symptoms. Some people also may develop a mild fever of about 100 F (37.7 C). Most symptoms will resolve in about 2 to 5 days. Gastroenteritis may cause dehydration during this short time period, mainly in children or debilitated adults. In this article, gastroenteritis with dehydration is considered severe gastroenteritis. For videos of how a child may appear with dehydration, see the link in the references section of this article.


People with symptoms of diarrhea, bloody diarrhea, nausea, or vomiting that last longer than 5 days, and often may have additional symptoms of fever (greater than 101 F, 38.3 C), malaise, dehydration, sepsis, or additional symptoms, for this article, will not be considered to have gastroenteritis.


Not all investigators or clinicians will agree with this designation and consider bloody diarrhea, vomiting more than 48 hours, fever higher than 101 F, dehydration, and relatively constant abdominal pain as symptoms of severe gastroenteritis.


However, since these symptoms are non-specific and are more frequently associated as part of a spectrum of symptoms that occur with a specific disease that needs medical care, often quickly, these symptoms are considered as part of those that may occur with a number of specific diseases.


Is gastroenteritis contagious?


The majority of causes of gastroenteritis are contagious (mainly viral, bacterial, and parasitic). In some instances where the cause of the gastroenteritis is not a pathogen (for example, food allergies, toxins that are ingested), gastroenteritis is not contagious.


Gastroenteritis has many causes. Viruses and bacteria are the most common.


Viruses and bacteria are very contagious and can spread through contaminated food or water. In up to 50% of diarrheal outbreaks, no specific agent is found. The infection can spread from person to person because of improper handwashing following a bowel movement or handling a soiled diaper.


Gastroenteritis caused by viruses may last one to two days. However, some bacterial cases can continue for a longer period of time.




Norovirus - Fifty to seventy percent of cases of gastroenteritis in adults are caused by thenoroviruses (genus Norovirus, familyCaliciviridae. This virus is highly contagious and spreads rapidly. Norovirus is the most common cause of gastroenteritis in the United States.


  • Noroviruses can be transmitted and infect individuals by
  1. contaminated food and liquids, 
  2. touching objects contaminated with norovirus and then placing the hands or fingers in the mouth,
  3. direct contact with an infected individual (for example, exposure to norovirus when caring or sharing foods, drinks, eating utensils with an affected individual, and
  4. exposure to infected individuals and objects in daycare centers and nursing homes.


  • Norovirus is often in the news when cruise ship passengers contract the virus, which causes gastroenteritis.


Rotavirus - According to the CDC, "Rotavirus was also the leading cause of severe diarrhea in U.S. infants and young children before rotavirus vaccine was introduced for U.S. infants in 2006. Prior to that, almost all children in the United States were infected with rotavirus before their 5th birthday.


Each year in the United States in the pre-vaccine period, rotavirus was responsible for more than 400,000 doctor visits; more than 200,000 emergency room visits; 55,000 to 70,000 hospitalizations; and 20 to 60 deaths in children younger than 5 years of age".


Other viruses that cause gastrointestinal symptoms include:


  • Adenoviruses - This virus most commonly causes respiratory illness; however, other illnesses may be caused by adenoviruses such as gastroenteritis, bladder infections, and rash illnesses.
  • Parvoviruses - The human bocavirus (HBoV), which can cause gastroenteritis belongs to the family Parvoviridae. 
  • Astroviruses - Astrovirus infection is the third most frequent cause of gastroenteritis in infants.




Bacteria may cause gastroenteritis directly by infecting the lining of the stomach and intestine. Some bacteria such as Staphylococcus aureus produce a toxin that is the cause of the symptoms. Staph is a common type of food poisoning.


Escherichia coli infection can cause significant complications. E. coli O157:H7 (one type of the bacteria) can cause complications in approximately 10% of affected individuals (for example, kidney failure in children [hemolytic-uremic syndrome or HUS), bloody diarrhea, and thrombotic thrombocytopenic purpura (TTP) in the elderly.


Salmonella, Shigella and Campylobacter


Salmonella, Shigella and Campylobacter are also common causes of illness.


  • Salmonella is contracted by ingesting the bacteria in contaminated food or water, and by handling poultry or reptiles such as turtles that carry the germs.
  • Campylobacter occurs by the consumption of raw or undercooked poultry meat and cross-contamination of other foods. Infants may contract the infection by contact with poultry packages in shopping carts. Campylobacter is also associated with unpasteurized milk or contaminated water. The infection can be spread to humans by contact with infected stool of an ill pet (for example, cats or dogs). It is generally not passed from human to human.
  • Shigella bacteria generally spreads from an infected person to another person.Shigella are in diarrheal stools of infected individuals while they are ill, and for up to one to two weeks after contracting the infection. Shigella infection also may be contracted from eating contaminated food, drinking contaminated water, or swimming or playing in contaminated water (for example, wading pools, shallow play fountains). Shigella can also be spread among men who have sex with men.


Clostridium difficile


Clostridium difficile (C difficile) bacteria may overgrow in the large intestine after a person has been on antibiotics for an infection. The most common antibiotics that pose a potential risk factor for C difficile include


  • clindamycin (for example, Cleocin),
  • fluoroquinolones (for example, levofloxacin [Levaquin'], ciprofloxacin [Cipro, Cirpo XR, Proquin XR]),
  • penicillins,
  • cephalosporins.


Other risk factors for C difficile infection are hospitalization, individuals 65 years of age or greater, and existing chronic medical conditions.


Parasites and Protozoans


These tiny organisms are less frequently responsible for intestinal irritation. A person may become infected by one of these by drinking contaminated water. Swimming pools are common places to come in contact with these parasites.


Common parasites include


  • Giardia is the most frequent cause of waterborne diarrhea, causing giardiasis. Often, people become infected after swallowing water that has been contaminated by animal feces (poop). This may occur by drinking infected water from river or lakes but giardia may also be found in swimming pools, wells and cisterns. 
  • Cryptosporidium (Crypto) is a parasite that lives in the intestine of affected individuals or animals. The infected individual or animal sheds theCryptosporidium parasite in the stool. Crypto may also be found in food, water, soil, or contaminated surfaces (swallowing contaminated recreational water, beverages, uncooked food, unwashed fruits and vegetables, touching contaminated surfaces such as bathroom fixtures, toys, diaper pails, changing tables, changing diapers, caring for an infected individual or handling an infected cow or calf). Those at risk for serious disease are individuals with weakened immune systems.


Other Common Causes of Gastroenteritis


Gastroenteritis that is not contagious to others can be caused by chemical toxins, most often found in seafood, food allergies, heavy metals, antibiotics, and other medications.


Although most people with gastroenteritis require no formal treatment, the key to a more rapid and safe recovery is good hydration. Home treatment consists of adequate fluid intake so that dehydration is prevented.


The recommended fluids are clear fluids (Pedialyte, especially for young children, Gatorade, Powerade, and other similar drinks) but not fruit juices or milk. If dehydration occurs, the affected individual should be evaluated by a health care practitioner, who is likely to begin IV rehydration, the treatment of choice for rapid rehydration.


Medications may be prescribed to reduce the symptoms of gastroenteritis, for example,promethazine (Phenergan), prochlorperazine (Compazine) or ondansetron (Zofran) may be prescribed to reduce vomiting. Some physicians suggest using these only as a suppository (or IV) since patients frequently just vomit the pills up.


Others may prescribediphenoxylate and atropine (Lomotil) orloperamide (Imodium) to slow diarrhea. Many clinicians simply suggest no treatment for gastroenteritis symptoms as all of the drugs have side effects, and the clinicians figure that if the patient stays well hydrated, the symptoms will soon stop anyway.


Once the gastroenteritis symptoms abate, especially vomiting, clinicians recommend a BRAT diet (bananas, rice, apples and toast) for a day or two before beginning a regular diet.


Individuals that have more serious symptoms, or other symptoms in addition to gastroenteritis need to be evaluated, diagnosed, and treated by a physician because the patient will likely have a specific disease that will need treatment. The treatment will depend on the cause of the illness (for example, salmonellosis or Clostridium difficile toxin). Administration of antibiotics and other treatments may be contraindicated for some of these diseases, so an accurate diagnosis is important.

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