What is Gastroenteritis?

Gastroenteritis, often referred to as the stomach flu or stomach bug, is an inflammation of the gastrointestinal tract, typically caused by viral, bacterial, or parasitic infections. The symptoms can vary depending on the cause and severity of the infection, but common symptoms of gastroenteritis include:


This is one of the hallmark symptoms of gastroenteritis. It may range from mild to severe and can be accompanied by abdominal cramps, bloating, and urgency to defecate.

Nausea and vomiting

Gastroenteritis often causes feelings of nausea, which may or may not lead to vomiting. Vomiting can contribute to dehydration, especially in severe cases.

Abdominal pain and cramping

Individuals with gastroenteritis frequently experience abdominal discomfort, which can range from mild cramps to more intense pain.


Many cases of gastroenteritis are accompanied by a fever. The fever may be low-grade or high, depending on the severity of the infection and the individual’s immune response.

Muscle aches

Some people with gastroenteritis may experience muscle aches and general feelings of malaise, similar to those experienced with the flu.


Headaches are common symptoms of many viral and bacterial infections, including gastroenteritis.

Loss of appetite

Due to nausea, abdominal discomfort, and other symptoms, individuals with gastroenteritis may experience a loss of appetite.


Diarrhoea and vomiting can lead to dehydration, which can manifest as symptoms such as dry mouth, decreased urination, dark-coloured urine, dizziness, and fatigue.

What is Gastroenteritis caused by?

Gastroenteritis, commonly known as the stomach flu, can be caused by various infectious agents, including viruses, bacteria, and parasites. Here are the main causes:


Viruses are the most common cause of gastroenteritis. The most prevalent viral causes include:

  • Norovirus: This highly contagious virus is responsible for a significant portion of gastroenteritis outbreaks worldwide, especially in crowded or semi-closed environments such as schools, cruise ships, and nursing homes.
  • Rotavirus: Primarily affects infants and young children, causing severe diarrhoea and vomiting. However, vaccination against rotavirus has reduced its prevalence in many parts of the world.
  • Adenovirus: Can cause gastroenteritis, particularly in children. It may also cause respiratory and eye infections.
  • Astrovirus: Another common cause of viral gastroenteritis, particularly in young children.
Virus causing Gastroenteritis
Virus causing Gastroenteritis


Bacterial gastroenteritis is typically caused by ingesting contaminated food or water.

Common bacterial pathogens include:

  • Salmonella: Often associated with raw or undercooked poultry, eggs, and unpasteurized dairy products.
  • Escherichia coli (E. coli): Certain strains of E. coli, such as E. coli O157:H7, can cause severe gastroenteritis. Contaminated food, particularly undercooked ground beef and unpasteurized dairy products, are common sources.
  • Campylobacter: Found in raw or undercooked poultry, unpasteurized milk, and contaminated water.
  • Shigella: Spreads through faecal-oral transmission, often in settings with poor sanitation.
  • Clostridium difficile (C. difficile): Typically associated with antibiotic use, which disrupts the normal gut flora, allowing C. difficile to proliferate and cause infection.
Bacteria Causing Gastroenteritis
Bacteria Causing Gastroenteritis


Parasitic gastroenteritis is less common in developed countries but can occur due to ingestion of contaminated food or water. Common parasites include:

  • Giardia lamblia: Often transmitted through contaminated water, causing diarrhoea, abdominal cramps, and bloating.
  • Cryptosporidium: Similar to Giardia, this parasite can contaminate water sources and cause gastrointestinal symptoms.
  • Entamoeba histolytica: Causes amoebic dysentery, characterized by severe diarrhoea with blood and mucus.
  • Toxins: Ingestion of certain toxins, such as those produced by Staphylococcus aureus or Bacillus cereus bacteria in improperly stored or handled food, can lead to symptoms of gastroenteritis.

In Paddington Medical, if indicated, we can test for all the various causes of gastroenteritis via the Stool or Faecal PCR. However, it should be noted that most patients do not require this test. Only if indicated, for example persistent symptoms, or worsening symptoms, we may offer the test. Once the test result is out, it can be used to guide treatment and prognosis.

What foods should I avoid if I have gastroenteritis?

When you have gastroenteritis, it’s important to avoid certain foods and beverages that can exacerbate symptoms or irritate your already sensitive digestive system. Here’s a list of items to avoid:

Dairy Products

If you’re lactose intolerant or experiencing lactose intolerance symptoms due to gastroenteritis, avoid dairy products, which can exacerbate diarrhoea, bloating, and gas. This includes:

  • Milk
  • Cheese
  • Ice cream
  • Yogurt

High-Fibre Foods

Fibre-rich foods can be harder to digest and may exacerbate diarrhoea and abdominal discomfort. Avoid foods high in insoluble fibre, such as:

  • Whole grains (whole wheat, bran)
  • Raw vegetables and fruits with skins (broccoli, cabbage, apples)
  • Legumes (beans, lentils)

Fatty or Greasy Foods

Greasy or fried foods can be difficult to digest and may worsen symptoms such as nausea and abdominal pain. Avoid:

  • Fried foods (fried chicken, French fries)
  • Fatty cuts of meat
  • Rich sauces and gravies

Spicy Foods

Spicy foods can irritate the gastrointestinal tract and worsen symptoms such as abdominal pain and diarrhoea. Avoid:

  • Spicy sauces (hot sauce, salsa)
  • Spicy seasonings (chili powder, cayenne pepper)
  • Spicy ethnic dishes (curries, Mexican cuisine)

Caffeine and Alcohol

Both caffeine and alcohol can have a dehydrating effect on the body and may exacerbate symptoms such as diarrhoea and nausea. Avoid:

  • Coffee
  • Tea (unless caffeine-free herbal tea)
  • Carbonated beverages containing caffeine
  • Alcohol

Highly Acidic Foods

Acidic foods and beverages can irritate the stomach lining and exacerbate symptoms such as heartburn and nausea. Avoid:

  • Citrus fruits and juices (orange juice, grapefruit)
  • Tomatoes and tomato-based products (sauce, salsa)
  • Vinegar and vinegar-based dressings

Artificial Sweeteners

Some artificial sweeteners, such as sorbitol and mannitol, found in sugar-free gum and candies, can have a laxative effect and worsen diarrhoea. Avoid products containing these sweeteners.

What can I eat if I have gastroenteritis?

If you have gastroenteritis, it’s essential to be mindful of what you eat to help alleviate symptoms and prevent further irritation to your digestive system. Here are some suggestions for foods and beverages that are generally gentle on the stomach and may be easier to tolerate during a bout of gastroenteritis:

Clear Liquids

Start with clear liquids to prevent dehydration and replenish lost fluids from diarrhoea and vomiting. Examples include:

  • Water
  • Clear broth
  • Oral rehydration solutions (ORS)

Simple Carbohydrates

Plain carbohydrates can provide quick energy without irritating the digestive system. Examples include:

  • Plain crackers or dry toast
  • Plain white rice
Porridge for Gastroenteritis
Porridge for Gastroenteritis

Boiled or Steamed Vegetables

Well-cooked, bland vegetables can provide nutrients without aggravating gastrointestinal symptoms. Examples include:

  • Boiled or steamed carrots
  • Boiled potatoes (without skins)
  • Steamed zucchini or squash

Lean Protein

If you tolerate protein well, opt for lean, easily digestible sources. Examples include:

  • Baked or broiled chicken (without skin)
  • Steamed Fish
  • Tofu

Remember the most important thing is to keep well hydrated. Drink plenty of fluids, in sips throughout the whole day.

Hydrate well to speed up recovery during Gastroenteritis
Hydrate well to speed up recovery during Gastroenteritis

When should I be worried about my symptoms of stomach flu or gastroenteritis? When should I see my doctor again?

While gastroenteritis is often a self-limiting illness that resolves on its own within a few days, there are certain signs and symptoms that may indicate a more severe or complicated case requiring medical attention. Here are some warning signs to watch for:

Signs of Dehydration

Dehydration is a common complication of gastroenteritis, especially if you’re experiencing frequent diarrhoea and vomiting. Seek medical attention if you experience:

  • Persistent thirst and dry mouth
  • Dark-coloured urine or decreased urine output
  • Dizziness or light-headedness
  • Weakness or fatigue
  • Sunken eyes
  • Rapid heart rate or breathing

Severe or Prolonged Symptoms

If your symptoms are severe, persistent, or worsening despite home care measures, it’s important to seek medical evaluation. This includes:

  • Severe abdominal pain or cramping
  • Bloody or black stools
  • High fever
  • Signs of neurological symptoms, such as confusion or severe headaches
  • Inability to keep down any fluids or food for more than 24 hours
  • Signs of dehydration as mentioned above

Specific Populations

Certain populations, such as infants, young children, elderly individuals, pregnant women, and those with weakened immune systems, are at higher risk of complications from gastroenteritis. If you or a loved one in these groups experience gastroenteritis symptoms, it’s important to seek prompt medical attention.

Travel History or Recent Antibiotic Use

If you’ve recently travelled to regions where gastroenteritis is common or have recently taken antibiotics, you may be at risk of certain types of bacterial or parasitic gastroenteritis that require specific treatment.

Persistent Vomiting or Diarrhoea

If you’re unable to keep fluids down due to persistent vomiting or experience severe diarrhoea that doesn’t improve after a couple of days, medical evaluation is warranted to prevent dehydration and electrolyte imbalances.

Other Concerning Symptoms

Trust your instincts. If you have other symptoms or concerns that worry you or interfere with your ability to function, it’s best to seek medical advice.

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