Gastroenteritis

What is gastroenteritis?

Gastroenteritis, sometimes called gastro, gastric flu or stomach flu, is a common condition caused by irritation and inflammation of the stomach and intestines.[1] It is usually the result of a viral or bacterial infection, but can also be caused by parasites, chemicals, or even certain medications. The main symptoms are nausea, vomiting, diarrhea and abdominal cramping. Although they can be very unpleasant, most cases of gastroenteritis clear on their own within a few days, without specific treatment. The main complication tends to be dehydration, particularly among young children and the elderly. To prevent this, it is important to replace fluids that are lost through vomiting and diarrhea.

Gastroenteritis symptoms

The symptoms of gastroenteritis can range from mild to severe, but typically include:

  • Diarrhea, which is often watery
  • Nausea and/or vomiting
  • Abdominal pain and cramps
  • Loss of appetite

These symptoms often appear suddenly. In addition, someone with gastroenteritis may present with the following:[2]

  • Bloating
  • Fever
  • Chills
  • Headache
  • Body aches
  • Lethargy

If there are symptoms of a more serious illness, or if the gastroenteritis does not resolve within a few days, it is important to seek medical advice. Things to watch out for are indications of severe dehydration (such as passing little to no urine, and dizziness that does not go away), blood or pus in the diarrhea, constant vomiting that makes it impossible to keep down liquids, or a fever over 38 degrees Celsius (100.4 F). In addition, if the affected person has recently returned from overseas travel, or has a serious underlying health condition like inflammatory bowel disease, it is advisable to see a doctor.[3]

Causes of gastroenteritis

Viruses are the most common cause of acute gastroenteritis, particularly in children. However, bacteria and their byproducts, parasites, toxic chemicals, and certain drugs can also cause the condition.

Viral gastroenteritis

A number of different viruses cause gastroenteritis. Although the condition is sometimes referred to as stomach flu, the influenza virus is not to blame. Flu shares some of the same symptoms – that is, headache, fever, and body aches, but it does not usually affect the stomach and intestines.[1]

The main types of viruses that cause gastroenteritis are norovirus, rotavirus, adenovirus and astrovirus. Of these, norovirus and rotavirus are the most common, with rotavirus responsible for the majority of cases of viral gastroenteritis in children.[3][4]

Viral gastroenteritis is highly contagious, leading to outbreaks in schools, hospitals, prisons and other places where large numbers of people are in close proximity. The virus is present in the stools and vomit of those who are infected, and is spread easily from person to person, particularly when people forget to wash their hands after using the toilet.

Infection typically occurs by sharing food, drink, eating utensils or towels with someone who has the virus, touching contaminated surfaces or objects and then touching your mouth, or consuming food or water contaminated with the virus. It has been suggested that swallowing airborne viral particles after someone has vomited may also be a possible route of transmission for some viruses. Raw or undercooked shellfish, especially oysters, can also be a source of the virus, as they may be contaminated from dirty water. However, this is relatively rare.[5]

Bacterial gastroenteritis

A range of different bacteria can also cause gastroenteritis. These include Salmonella, Campylobacter, Shigella, Escherichia coli and Clostridium difficile.[6] Some of these bacteria can be transmitted from person to person, but they are most often spread through contaminated food and water.

The bacteria are frequently ingested from undercooked meat, eggs and fish, as well as unpasteurised milk and juices, and untreated water. They can also be acquired from food that is improperly stored or prepared, as well as from raw fruits and vegetables that are not thoroughly washed in clean water. Contact with reptiles, birds and amphibians can also be a route of transmission for salmonella.

Bacterial gastroenteritis is a common cause of “traveler’s diarrhea”, a type of gastroenteritis that frequently affects travelers to developing countries. It is often the result of poor food hygiene in local restaurants.[7]

Some cases of gastroenteritis are not caused by the bacteria themselves, but by toxins that they release. The harmful byproducts of certain types of bacteria can contaminate food, causing food poisoning when ingested. These byproducts are called exotoxins, and usually cause symptoms within 12 hours of consumption. This type of gastroenteritis typically resolves within 36 hours.[6]

Parasite-related gastroenteritis

Gastroenteritis can also be caused by infection with intestinal parasites. The two most commonly implicated are giardia and cryptosporidium.[6] These parasites are found all over the world, and are typically acquired through contaminated water or contact with infected animals.

Giardia can also be spread from person to person, for example in daycare centers, if people do not wash their hands after using the toilet. Infection with giardia is known as giardiasis, and can become chronic if not treated properly, causing malabsorption of nutrients. Cryptosporidium infections, which are usually acquired through swimming in and accidentally swallowing contaminated water, typically resolve on their own within two weeks.

The amoeba E. histolytica is another type of parasite that can cause gastroenteritis. It is not common in developed countries, but should be ruled out as a cause of the condition if the affected person has recently traveled to countries in Africa, Asia and Central and South America.[8]

Other types of gastroenteritis

While uncommon, in susceptible people gastroenteritis can be an adverse effect of certain medications. These include antacids, antibiotics, laxatives, anthelmintics, and some drugs used in cancer treatment. Radiation therapy can also cause symptoms similar to those of gastroenteritis.

In addition, gastroenteritis can be triggered by the ingestion of heavy metals like lead, mercury and arsenic. It can also be caused by plant toxins, in the case of ingesting poisonous plants and mushrooms.[9] If any of these causes are suspected, medical advice should be sought without delay.

Diagnosis of gastroenteritis

Many cases of gastroenteritis go away on their own, without treatment, and without the need for a formal diagnosis by a doctor. However, if the condition does not clear within a few days, or if there are any causes for concern, such as blood or pus in the stools, constant vomiting or diarrhea, a high fever, or symptoms of dehydration (for example, dry mouth, headache, and infrequently passing small amounts of urine), it is important to see a medical practitioner to identify the cause of the illness. This is also the case if the affected person has recently traveled, or has a weakened immune system or underlying health condition.

The treatment prescribed will differ depending on what is causing the gastroenteritis. Medical practitioners typically start by taking a medical history and performing a physical examination. They may then order blood and stool tests if they deem it necessary.[2]

Gastroenteritis treatments

In most cases, basic supportive treatment is sufficient. This includes bed rest, oral rehydration, and medication to manage the nausea, vomiting and diarrhea.[6] As long as there are no indications of a more serious condition, or severe dehydration, gastroenteritis can generally be treated at home.

It is very important that a person with gastroenteritis drink plenty of fluids. They should take frequent small sips in between vomiting or bowel movements. To help prevent or treat mild dehydration, oral rehydration drinks, available from pharmacies, can be used. These are different to sports drinks and carbonated beverages, which are not as effective in replacing lost electrolytes. If a person with gastroenteritis is unable to keep any liquids down, or is becoming severely dehydrated, they can be admitted to hospital to receive intravenous fluids via a drip.

To avoid spreading the infection to others, a person with gastroenteritis should stay home until their symptoms have completely cleared.[4] They should also take care to wash their hands thoroughly after using the toilet, and before preparing or eating food.

Antiemetics, antibiotics and other medication

If the nausea and vomiting is severe, an antiemetic medicine like ondansetron may be helpful.[6] Antiemetics lessen the feelings of nausea and prevent vomiting, which can help the person with gastroenteritis to rehydrate and rest. However, these medicines should not be used if a more serious condition is suspected.

Anti-diarrheal medication such as loperamide can also be taken, but should be avoided in certain cases.[6] These include where the person has recently taken antibiotics, where there is blood or pus in the stool, or where a more serious condition is suspected. In these cases, it is advisable to consult a doctor first.

Antibiotics are not widely prescribed for gastroenteritis, as they are only effective in certain cases of bacterial gastroenteritis. They may be prescribed for traveler’s diarrhea, or infections with shigella or campylobacter.[6] Doctors will often test for the specific bacteria before prescribing antibiotics.

If a painkiller is needed, paracetamol is preferred over ibuprofen and other medication that can cause further irritation to the digestive tract. Where the cause of the gastroenteritis is a parasite, an anti-parasitic medication will be prescribed.

Home remedies for gastroenteritis

There are a number of home remedies that can help with the treatment of gastroenteritis. These include:[10]

  • Drinking lots of fluids, like water, clear broths, and caffeine-free sports drinks, as well as oral rehydration mixes, to replace electrolytes lost through diarrhea and vomiting
  • Sucking on ice chips when nothing else will stay down
  • Resting as much as possible
  • Letting the stomach settle, then reintroducing food slowly, beginning with bland, simple foods like rice, crackers, bananas and clear chicken soup
  • Avoiding dairy, as well as rich and fatty foods, until recovery is complete
  • Avoiding caffeine, alcohol and nicotine until recovery is complete

Probiotics may slightly shorten the duration of diarrhea,[6] so they can be considered as a complementary remedy in the treatment of gastroenteritis.

Preventing gastroenteritis

Practicing good hygiene is the best way to prevent the spread of gastroenteritis. These precautions should be taken:[2][5][6]

  • Wash your hands thoroughly after using the toilet, after contact with animals, before preparing or eating food, and after changing a diaper. Use soap and water, or hand sanitizer if water is not available. Teach children to do the same.
  • Make sure that food is stored properly and prepared hygienically.
  • Keep the kitchen and bathroom clean. Disinfect surfaces regularly, using bleach diluted in water (dilute according to the instructions on the product).
  • When someone has gastroenteritis, clean and disinfect the toilet after each bout of vomiting or diarrhea.
  • Do not share towels, washcloths or utensils with someone who is ill. Wash these separately, using hot water.
  • Stay off work or school until 48 hours after the symptoms have cleared.
  • When traveling, take care to avoid tap water (including ice cubes) and potentially contaminated food if the area seems to lack adequate sanitation.
  • If you have diarrhea, avoid swimming.
  • Vaccinate children against rotavirus.

Gastroenteritis in children

Young children are particularly susceptible to rotavirus infections, because they often forget to wash their hands after using the toilet and before eating food. They have also not yet built up a resistance to the virus. It is estimated that all children will have at least one bout of viral gastroenteritis before they are five years old, and many will have multiple episodes a year.[11]

In most cases, gastroenteritis does not need to be formally diagnosed by a doctor, and the illness clears on its own within five to seven days. However, as with adults, if there are any indications of a more serious condition, medical advice should be sought. These include: symptoms of dehydration, vomiting for more than three days, diarrhea for more than a week, blood, mucus or pus in the stools, a high temperature (over 38 degrees Celsius or 100.4 F), shortness of breath or rapid breathing, confusion, stiff neck, rash, green vomit, severe stomach pain, swelling of the abdomen, or a bulging fontanelle (in infants). In addition, if the child has a weakened immune system or underlying illness, or has recently traveled, it is important to see a doctor.

Young children, particularly those under a year old, are at high risk of dehydration. Caregivers need to monitor for the following symptoms,[11] and seek medical advice if they are present:

  • Dry eyes and mouth
  • No tears when crying
  • Sunken eyes
  • Irritability and drowsiness
  • Reduced urine
  • Cold hands and feet
  • Pale or blotchy skin
  • Rapid breathing
  • A sunken fontanelle in infants

As long as there is no indication of dehydration or another serious condition, children can generally be treated at home. Treatment for gastroenteritis should be supportive, with an emphasis on rest and rehydration.

The child should be encouraged to drink lots of fluids. Avoid carbonated drinks and juices, as they may worsen the diarrhea. Water and oral rehydration mixes are recommended. As soon as the vomiting is under control, the child should be encouraged to eat simple solid foods like bread, rice and plain pasta. Infants should be fed breast milk or their other milk feeds as usual.[3]

Antiemetics, anti-diarrheals and other medication should be given to children only on the recommendation of a medical practitioner. Paracetamol can be used to reduce a temperature and alleviate aches and pains.

Other names for gastroenteritis

  • Stomach flu
  • Infectious diarrhea

Gastroenteritis FAQs

Q: Is gastroenteritis contagious?
A: Yes. Most cases of gastroenteritis are highly contagious, and can be spread easily from person to person. The exception is gastroenteritis caused by drugs, chemicals or poisonous substances. To prevent the transmission of bacterial, viral or parasite-related gastroenteritis, it is important to practice good hygiene. A person may be contagious for anything from several days up to two weeks after recovery from viral gastroenteritis.[12]

Q: How long does gastroenteritis last?
A: Most cases of gastroenteritis clear within a few days to a week. In children, it may take five to seven days. If the symptoms persist, it is important to consult a medical practitioner.

Q: When should I see a doctor about gastroenteritis?
A: It is advisable to consult a medical practitioner if:

  • You are vomiting a lot and cannot keep fluids down
  • You suspect that you are becoming dehydrated
  • You notice any blood in your vomit or stools
  • You have severe stomach pain
  • You have a high temperature that does not go down
  • You have persistent diarrhea

In addition, if you are elderly, pregnant, have a chronic health condition like diabetes, or have a compromised immune system, it is also important to consult a doctor.[13]

Q: Should I be worried about gastroenteritis during pregnancy?
A: Pregnant women are just as susceptible to gastroenteritis as everyone else. Most cases of the illness will clear on their own without any complications, and can be treated with rest and rehydration. Medicines should be used with caution – a medical practitioner should be consulted before taking any antiemetics or other medication.[14] If the gastroenteritis does not clear, there is a fever, or there are indications of a more serious condition, medical advice should be sought without delay.


  1. eMedicineHealth. “Gastroenteritis.” Accessed July 19, 2017.

  2. Better Health Channel. “Gastroenteritis.” Accessed July 19, 2017.

  3. NHS Choices. “Diarrhea and vomiting (gastroenteritis).” Accessed July 19, 2017.

  4. NHS Foundation Trust. “Gastroenteritis caused by Norovirus and other viruses.” October, 2013. Accessed July 19, 2017.

  5. National Institute of Diabetes and Digestive and Kidney Diseases. “Viral Gastroenteritis.” April, 2012. Accessed July 19, 2017.

  6. Merck Manuals. “Overview of Gastroenteritis.” May, 2017. Accessed July 20, 2017.

  7. Centers for Disease Control and Prevention. “Travelers’ Diarrhea.” June 13, 2017. Accessed July 20, 2017.

  8. American Family Physician. “Common Intestinal Parasites.” March, 2004. Accessed July 24, 2017.

  9. Merck Manuals. “Drug-Related Gastroenteritis and Chemical-Related Gastroenteritis.” May, 2017. Accessed July 25, 2017.

  10. Mayo Clinic. “Viral gastroenteritis (stomach flu) - Lifestyle and home remedies.” December 2, 2014. Accessed July 25, 2017.

  11. NHS Direct Wales. “Gastroenteritis in children.” May 30, 2017. Accessed July 26, 2017.

  12. Mayo Clinic. “Viral gastroenteritis (stomach flu) - How long am I contagious if I have the stomach flu?” January 17, 2015. Accessed July 26, 2017.

  13. Patient. “Gastroenteritis in Adults.” September 20, 2017. Accessed October 10, 2017.

  14. Mom Tricks. “How to Deal With a Nasty Stomach Virus When Pregnant.” July 22, 2017. Accessed July 26, 2017.