Gastroenteritis

Your health expert: Mr Christian Macutkiewicz, Consultant General and Hepato-Pancreatico-Biliary Surgeon
Content editor review by Rachael Mayfield-Blake, May 2022
Next review due May 2025

Gastroenteritis is an infection of your stomach or bowels. You may hear it called a tummy bug, stomach flu or gastric flu. It causes diarrhoea, sickness and tummy pain. Gastroenteritis is usually mild and clears up on its own after a few days. But it can be more serious for some people.

About gastroenteritis

Gastroenteritis is very common. In the UK, around one in four people each year will have a gastroenteritis infection.

For most people, gastroenteritis is a mild tummy upset that you can treat at home. But some people can develop severe diarrhoea and sickness. This can lead to dehydration and other complications, which may need medical treatment. This is more likely in babies, older people, and those with underlying health conditions.

Causes of gastroenteritis

Gastroenteritis may be caused by infection with a virus, bacteria or parasites. When these get into your body, they damage the lining of your tummy or bowel. You won’t usually know what’s caused your gastroenteritis. The cause doesn’t normally make a difference to your treatment.

Viral gastroenteritis

In the UK, most gastroenteritis is due to viruses. The winter vomiting bug (norovirus) is the most common type of viral gastroenteritis. Other viruses that cause gastroenteritis include rotavirus and adenovirus. These viruses are more common in children.

You can catch viral gastroenteritis if tiny particles from the vomit or poo of an infected person get into your mouth. This might be through:

having close contact with an infected person – particles may spread through the air as well as through direct contact
touching objects and surfaces that an infected person has touched
eating food (such as oysters) or drinking water that contains the virus

Bacterial gastroenteritis

Bacterial gastroenteritis is usually caused by food poisoning. This is when you eat or drink something that contains bacteria or toxins from bacteria. The bacteria that most commonly cause gastroenteritis include:

Campylobacter – most often found in undercooked chicken, unpasteurised milk and untreated water
Salmonella – from foods such as meats, raw eggs, milk and dairy
Escherichia coli (E. coli) – most often from meat, salad products and unpasteurised milk

Parasitic gastroenteritis

Parasites are tiny creatures that live on other animals. Parasites that cause gastroenteritis include Cryptosporidium, Entamoeba and Giardia. You may get an infection by:

contact with an infected animal
drinking infected water
eating food that contains the parasite
sometimes, contact with someone who has the infection

Travellers’ diarrhoea

Travellers’ diarrhoea is a gastroenteritis infection that you catch in a different country. It can be caused by viruses, bacteria or parasites. You usually catch it through eating contaminated food or drinking contaminated water

Symptoms of gastroenteritis

Gastroenteritis symptoms may include:

diarrhoea (very loose and watery poo, sometimes containing blood or mucus)
feeling sick or being sick
tummy pain or cramps

Diarrhoea and sickness usually come on suddenly.

You may also:

have a temperature (fever)
feel generally unwell
lose your appetite
have aching muscles
have headaches

For viral infections, you’ll usually get symptoms about a day after catching the infection. It usually takes longer for symptoms to appear after infection with bacteria or parasites. Gastroenteritis symptoms can last for up to a week, sometimes more.

Self-help for gastroenteritis

Most people with gastroenteritis get better at home after a few days and don’t need any specific treatment.

Stay at home and rest until you feel better. You shouldn’t go into work or mix with others for at least 48 hours after your diarrhoea and sickness have stopped. This stops you spreading the infection. If your child has the infection, they should stay off nursery or school for at least 48 hours after their symptoms stop.

Keeping hydrated

If you have diarrhoea and sickness your body will be losing more fluid than usual. It’s important to replace this by drinking plenty of fluids to keep hydrated. It’s best to try to drink small amounts regularly. Plain water and clear fluids are best. Keep a glass of water or water bottle nearby that you can keep sipping from.

It’s best for children not to have fruit juices or fizzy drinks while they have symptoms. If your baby has gastroenteritis, keep to their usual feeds – whether that’s breastfeeding or other milk feeds.

Oral rehydration solutions

If you’re becoming dehydrated, you may find oral rehydration solutions helpful. These are special drinks that you make up using powder from a sachet. You can buy them from a pharmacy, supermarket or online. They’re suitable for children too.

Oral rehydration solutions have the right mix of sugars, minerals and salts to help you replace lost water and salt. These products may also be useful if you’re at greater risk of dehydration, perhaps because you’re older or have other illnesses. Ask a pharmacist if an oral rehydration solution might be suitable for you.

What to eat with gastroenteritis

There is no recommended diet for gastroenteritis. It’s better to just eat as and when you feel able to. Some people prefer to start with bland foods and small, light meals. Examples include:

toast
crackers
rice
lean meats such as chicken
clear soups
potatoes
carrots and squash

It’s a good idea to avoid anything fatty or spicy at first. You may also find it hard to tolerate dairy foods, wholegrain breads and citrus fruits to begin with. But sticking to bland foods for a long time may mean you don’t get all the nutrients you need. So, it’s important to get back to your normal diet once you feel able to and are drinking enough fluids. This is especially important for children.

Anti-diarrhoea medicines

You don’t usually need medicines for gastroenteritis. But there may be times when you find medicines useful if you need to stop diarrhoea quickly. This might be if you’re travelling or are somewhere you can’t get to a toilet easily.

Medicines for diarrhoea include loperamide (also known as Imodium®). You can buy loperamide for adults and children over 12 years from pharmacies, shops and online. It’s not usually recommended for children under the age of 12, but sometimes doctors may prescribe it. Don’t take these medicines if you have a fever or have blood or mucus in your poo, because they could make you feel worse.

When to seek medical help for gastroenteritis

You won’t usually need to contact a doctor about gastroenteritis. Most people with gastroenteritis get better at home without seeing a doctor. But sometimes gastroenteritis can become more serious and you may need medical help. Contact your GP if any of the following apply.

You have signs of severe dehydration. These include passing little or no urine, feeling weak, dizzy or confused, and having headaches and muscle cramps. See our Complications section for more details on dehydration.
You’re constantly being sick and can’t keep down any fluids.
You have severe or uncontrollable diarrhoea that’s making you dehydrated.
You have diarrhoea with blood or pus in it.
You’ve recently been abroad.
You have other illnesses or long-term conditions or a weak immune system.
You’re too unwell to care for yourself properly at home and don’t have anyone who can look after you.
You aren’t starting to feel better within a week or are still having diarrhoea by this time.

Babies under one year are at particular risk of developing dehydration. Signs of dehydration in children and babies include peeing less, seeming irritable, and having a dry mouth and sunken eyes. Seek medical help if you think a child with gastroenteritis is dehydrated.

Medical treatment for gastroenteritis

To avoid spreading the infection, your GP may suggest a telephone consultation rather than seeing you in person. They’ll ask you questions about your symptoms and medical history. They’ll want to know if you’ve been abroad recently or if you’ve eaten anything that may have given you food poisoning. If you do see them in person, they may examine you too.

If your doctor thinks you may have a bacterial infection, they will probably ask you to provide a poo sample. This will be sent to a laboratory for testing. If this shows you have bacterial gastroenteritis, your doctor may prescribe antibiotics. You wouldn’t usually have antibiotics for most types of gastroenteritis.

If you become very dehydrated or unwell, you may need to be admitted to hospital. In hospital, you can have fluids directly into your bloodstream through a drip in your arm.

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Complications of gastroenteritis

Gastroenteritis is usually a mild illness that you recover from quickly. But in a few people, it can lead to more serious complications.

Complications are more likely to affect:

young children
older people
people with other health problems
people with a weak immune system – from either a health condition or medication

Complications can also depend on exactly what’s caused your infection. Certain complications are only linked to bacterial infections.

Dehydration

If diarrhoea or sickness is very bad, this can cause dehydration. This happens when you’re losing lots of fluid and you don’t drink enough fluid to make up for it. Babies younger than one year are particularly at risk. Sickness and diarrhoea can also affect the balance of salts and minerals in your body.

If you’re severely dehydrated, you may:

pass little or no urine
feel weak, dizzy or confused
have headaches
have muscle cramps

Babies or young children may also seem irritable and have a dry mouth and sunken eyes. Contact your GP if you think you or your child are severely dehydrated. Being very dehydrated can be dangerous and it’s important to get the right treatment.

Other complications

Other complications of gastroenteritis include the following.

Lactose intolerance. This can make you sensitive to dairy products. It’s usually temporary.
Irritable bowel syndrome (IBS). This can cause ongoing symptoms, like diarrhoea, constipation and bloating.
Reactive arthritis. This is a type of arthritis that usually only lasts for a short time. It causes swelling in your joints and sore eyes.
Haemolytic uraemic syndrome. This is a serious kidney problem, often causing bloody diarrhoea. It’s more common in young children.
Toxic megacolon. This is a serious complication in which part of your bowel becomes inflamed. It can be life-threatening if you don’t get treatment quickly.

Preventing spread of gastroenteritis

If you or someone in your household has gastroenteritis, take the following measures to reduce the risk of spreading it.

Wash your hands with soap and warm, running water after going to the toilet. If you have a baby with gastroenteritis, wash your hands after changing their nappy.
Wash your hands before and after preparing, serving or eating food.
Wash dirty clothing or bed linen separately and at the highest temperature possible. The washing machine shouldn’t be more than half full, to make sure everything is properly cleaned and well-rinsed.
Clean toilet seats, flush handles, taps, surfaces and toilet door handles every day with detergent and hot water. Use disinfectant and a disposable cloth to clean the toilet.
Don't share towels or flannels.
If you’ve been diagnosed with the parasites Cryptosporidium or Giardia, there are rules about swimming. Don’t go swimming for at least two weeks after your diarrhoea has stopped.
Stay off work or school for at least 48 hours after your diarrhoea or sickness has stopped. If you can, stay away from hospitals and GP surgeries too. This will stop spreading the infection to people who are most likely to get complications.

Babies can be immunised against rotavirus, a common cause of gastroenteritis. They can have this at two months and then a second dose at three months.

Before travelling to another country, you can check if you need to take any precautions for that country at www.travelhealthpro.org.uk. Information includes any vaccinations you need and details such as if you should drink only bottled water.

There isn’t a particular diet you need to follow. When you’re ready to start eating, you may prefer to start with bland foods and avoid anything fatty or spicy. Aim to get back to your normal diet as soon as you can. If you don’t feel like eating, the most important thing is to keep your fluids up. See our section on self-help for more information about diet.

The main symptoms of gastroenteritis include diarrhoea and feeling or being sick. These usually come on suddenly. You may also get tummy pains or cramps and have other symptoms such as a fever. Most people feel better within a week. See our section on symptoms to find out more.

Most people have a mild illness and start to feel better after a few days. Most people find their symptoms have gone within a week. But sometimes the condition may last for longer. It can depend on exactly what’s causing your gastroenteritis and if you have any health conditions that can make it more serious.

Viral infections are the most common cause of gastroenteritis in the UK. The winter vomiting bug (norovirus) is the most common type of viral gastroenteritis. Bacteria such as E. coli and Salmonella can also cause gastroenteritis, as can parasites. See our section on causes for more information.

There are lots of ways to catch gastroenteritis. Viral gastroenteritis is contagious. You can catch it from someone who’s infected if you encounter particles of poo or vomit. You can also catch it by eating food or drinking water contaminated with viruses, bacteria or parasites. See our section on causes to find out more.