Gastroenteritis (Stomach Flu)

Often incorrectly referred to as the ‘stomach flu’, gastroenteritis is a condition in which a person experiences temporary inflammation of the stomach and/or intestines. This inflammation leads to diarrhea and/or vomiting, as well as complications from these symptoms, such as abdominal pain, dehydration, and fatigue. Gastroenteritis is common, especially in children, but there are many different causes of this condition.


Gastroenteritis symptoms often begin suddenly and, in most types, last for one to three days in healthy adults, but can last longer in young children, the elderly, and those who have suppressed immune systems.

Most individuals with gastroenteritis will experience both diarrhea and vomiting, but some experience only one of these symptoms. Diarrhea is often very watery (type 7 on the Bristol stool chart), and can be bloody if the source of gastroenteritis is bacterial. Persistent diarrhea and vomiting can lead to abdominal pain, stomach cramps, loss of appetite, and dehydration. In young children, diarrhea and vomiting can cause an electrolyte imbalance, which is very dangerous and can lead to death if untreated.

In viral gastroenteritis, other symptoms such as fever, headache, body aches, chills, and fatigue can occur, leading to much of the confusion between the flu and gastroenteritis. The flu is a respiratory illness caused by infection with the influenza virus, and although many other symptoms are similar between the flu and gastroenteritis, the flu rarely causes vomiting and diarrhea.

Long-Term Effects

While the body typically clears an infection within a few days, sometimes there can be lasting effects. Gastroenteritis can modify the microbiome balance, leading to a decrease in the diversity and quantity of good bacteria in the gut, which can cause health complications in the long-term.1 One study found that approximately one in five of those affected with norovirus experienced significant microbiota alterations, although it is unclear how many of them will develop complications from this imbalance.2

One potential outcome of gastroenteritis is a type of irritable bowel syndrome (IBS) known as post-infectious IBS. Studies have found that post-infectious IBS affects between 5-32% of those who experience gastroenteritis.3 However, the prognosis is good for this type of IBS, with symptoms typically gone soon after developing, without need for treatment. In cases of bacterial gastroenteritis, it can take a few years to resolve, but if it’s caused by viral infection, then symptoms are usually gone within a few months.3 Although this type of IBS is uncomfortable, it does not lead to any other adverse affects, and doesn’t increase the risk of other diseases or disorders after symptom resolution.

Some other potential, but rare, complications from gastroenteritis include developing ulcerative colitis, aortic aneurysm, or reactive arthritis in the months after the infection.4


Viral, bacterial, or parasitic infections cause most cases of gastroenteritis. These are communicable infections, which can be spread through contact with another person who is sick, contact with an item recently touched by someone with infectious gastroenteritis, or the consumption of contaminated food or water. Many individuals develop gastroenteritis while travelling, especially in developing countries.

The most common cause of gastroenteritis is norovirus. When someone gets the ‘stomach flu’, it is typically an infection with one of the viruses in the norovirus family. Norovirus is highly contagious, and is often responsible for sickness outbreaks on cruise ships, in nursing homes, and in schools. Symptoms typically last only a day or two.5

Until recently, infection with rotavirus was the most common cause of gastroenteritis in children. Symptoms last for up to a week, and can be very severe. In young children, particularly those under five years-of-age, gastroenteritis from rotavirus can lead to serious complications from dehydration if untreated, and can even be fatal. However, since 2006, there have been effective vaccines for this virus, which have drastically reduced the incidence of children with rotavirus infection and gastroenteritis hospitalized in Canada. For more information on the rotavirus vaccine, see the article Rotavirus Vaccine Success.

Bacteria cause many cases of foodborne gastroenteritis. These include infections with E. coli and various species within the salmonella, campylobacter, shigella, staphylococcus, and yersinia genera. For some of these, the bacteria themselves cause gastroenteritis, but in others, the bacteria produce toxins that damage the digestive tract and cause gastroenteritis. Food products purchased from stores could be tainted with harmful bacteria, and food prepared at home or at a restaurant with inadequate sanitation protocols could become contaminated. These bacteria can also spread from person-to-person.

Protozoa such as Giardia lamblia and Cryptosporidium parvum can also cause gastroenteritis. Most individuals who become infected with these parasites do so from consuming contaminated water. They also spread from contact with an infected individual. These types of infections are more common when travelling in developing countries.

Antibiotics might increase the risk of gastroenteritis in susceptible populations by disturbing the balance of gut microbiota.


Gastroenteritis affects millions of Canadians each year. While it is difficult to accurately count the number affected, approximately four million Canadians, or about one in eight, get food-borne gastroenteritis each year. Of these, 11,600 are hospitalized and 238 cases result in death from complications.6


Your physician will likely make a diagnosis of gastroenteritis based off symptoms alone. They might request a stool test to check for the presence of certain viruses, bacteria, and protozoa in order to determine the source of the gastroenteritis.

Prevention and Management

Treatment will vary depending on the source of gastroenteritis. However, since some form of highly contagious agent usually causes gastroenteritis, maintaining a healthy hand-washing routine, and staying home when sick, can help avoid the spread of the illness and prevent community outbreaks.

There are no medications available to treat viral gastroenteritis. Instead, treatment focuses on symptom management and preventing complications. In the rare cases of bacterial gastroenteritis, an antibiotic might be useful.

While travelling, drink bottled water and beverages if possible – and make sure they are sealed before you open them – and only consume local water after boiling it for three minutes. Brush your teeth with bottled water and keep your mouth closed while showering. Avoid raw fruits and vegetables unless they have a skin you can peel (bananas, citrus, avocado, etc.). Stick to well cooked foods while eating out, and don’t consume any ice or undercooked meat or fish. Try to avoid street vendors, which are more likely to be contaminated than restaurants. As with gastroenteritis at home, regular hand-washing is important.

The rotavirus vaccine is an effective means of preventing children from developing this dangerous form of gastroenteritis. The National Advisory Committee on Immunization recommends that infants receive their first dose of rotavirus vaccine between 6 weeks and 15 weeks-of-age, and their final dose before 32 weeks-of-age.7 Depending on the brand, they will need 2-3 doses of vaccine, which need to be at least 4 weeks apart.7


Stop the Spread of Gastroenteritis

  • wash your hands
  • stay home
  • don’t bring ill children to school or daycare
  • vaccinate infants against rotavirus

Managing Gastroenteritis

  • stay hydrated
  • get plenty of rest
  • eat small amounts of nutritious foods as tolerated
  • avoid foods that are spicy, sugary, or fatty
  • get medical help if symptoms are severe

Treating Symptoms

For most cases of gastroenteritis, home treatment is adequate. It is important to drink plenty of fluids, but sip slowly rather than chug large amounts to ensure consistent hydration and avoid increased vomiting.

If your infant is sick, continue their normal feeding routine, whether it is breast milk or formula. It is useful for children who experience vomiting and diarrhea, and adults who have had these symptoms for 24 hours or longer, to consume electrolyte preparations. Electrolytes are the salts and minerals that the body uses to conduct electrical impulses that allow the muscles and nervous system to function correctly. Excessive diarrhea and vomiting, and the resulting severe dehydration, can cause an imbalance in these electrolytes, which is potentially dangerous if left untreated. However, there are many commercial products focused on providing electrolytes for children and adults during illness, such as Pedialyte® and Hydralyte®. Avoid sports drinks, which tend to be higher in sugar and lower in electrolytes. For mild gastroenteritis, coconut water can be effective.8

There are also many recipes for homemade electrolyte drinks available. It is important to be careful following recipes for homemade electrolyte drinks and to use recipes from health professionals. Recipes made with the wrong ratios can be ineffective at replenishing electrolytes adequately, and liquids with too much salt can increase diarrhea. These also might not taste as good as commercial varieties, and could be off-putting for some children, especially when they are already ill and having trouble consuming anything. One simple version is to combine 360 ml of unsweetened orange juice, 600 ml of cooled, previously-boiled water, and 2.5 ml of salt.9

During an episode of gastroenteritis, it is important to eat when you are able to, but avoid high-fat foods, high sugar foods, very high-fibre foods, spicy foods, dairy products such as milk and cheese, coffee, and alcohol, as these can irritate the gastrointestinal tract and increase symptoms. Start with very small portions, and gradually increase to the level your digestive tract can handle without becoming ill. In the past, physicians advised patients to consume simple foods such as dry toast, crackers, and applesauce, but now they recommend eating more nutritious foods to help provide the body with the sustenance it needs to heal. Foods that are both beneficial and easy to tolerate include fresh fruits, cooked vegetables, lean meats and fish, eggs, rice, pasta, bread, and low-fat yogurt (if you are not lactose intolerant).10

Make sure to get plenty of rest and stay at home. This goes for every member of the family, any children who are sick should stay home from school or daycare to prevent spreading gastroenteritis to their classmates. Always wash your hands after going to the bathroom or changing a diaper, and before preparing any food.

Avoid using nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Advil®), acetylsalicylic acid (Aspirin®), or naproxen (Aleve®) to control pain, because these can further irritate the digestive tract. Speak with a physician before taking any medications to stop vomiting (antiemetic) or diarrhea (antidiarrheal).

Taking a probiotic supplement during and after infection with gastroenteritis might help reduce some of the potential damage to the gut microbiome balance,11 but you should speak with your physician or pharmacist to help decide which product would be best for you.

When to Seek Medical Help

If you, or the person you are caring for, experience fever or persistent vomiting/diarrhea that lasts more than a couple days, or stools that are black and tarry or contain visible blood, especially in young children, then you should consult your physician.

Some symptoms, such as producing no urine or only very small amounts of urine, having a very dry mouth or sunken eyes, experiencing a fast or irregular heartbeat or quickened breathing, feeling dizzy and light-headed, and not being alert can point to severe dehydration. Blurred or double vision, trouble swallowing, trouble breathing, or muscle weakness after eating canned food could be signs of botulism. In either of these cases, call 911 or visit the hospital immediately.12


Most healthy adults will recover from a bout of gastroenteritis within a few days with no lasting complications. However, young children, elderly individuals, pregnant women, and those with weakened immune systems are more likely to experience severe dehydration or an electrolyte imbalance without proper care. In addition, gastroenteritis can put some individuals at an increased risk of developing other diseases and disorders. Proper handwashing techniques and staying home while ill can help prevent the spread of the contagion that is causing your gastroenteritis. If you are concerned for yourself or someone you are caring for, make sure to consult a medical professional.

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