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.

  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.