What causes gastroenteritis?

Gastroenteritis is usually caused by a virus infecting the gut. It can also be caused by bacterial infections or by infections with parasites.

Other conditions can cause stomach and intestine inflammation, such as inflammatory bowel disease, but doctors generally use the term gastroenteritis to mean an infection, instead of inflammation from something else.

If you think you or your child have gastroenteritis, find out what to do next by clicking here. This will tell you if you need to see a doctor and how to treat it.

In this series of articles centred around gastroenteritis you can read about symptoms of gastroenteritis, the causes of gastroenteritis,and treatments for gastroenteritis -all written by one of our expert GPs.

The rest of this feature will take a in-depth look at the causes of gastroenteritis as, at Patient, we know our readers sometimes want to have a deep dive into certain topics.

What causes gastroenteritis?

Viruses

Viruses are the most common cause of gastroenteritis. Examples of viruses that cause gastroenteritis include:

• Rotavirus - the most common cause of gastroenteritis in infants and young children. It's less common in adults, who usually have built up some immunity against it. There is an effective vaccine against rotavirus, which greatly reduces the risk of children becoming seriously unwell if they catch it.

• Norovirus - an extremely contagious virus that typically causes outbreaks, particularly amongst people in close contact with each other.

• Other types of virus, like adenoviruses, enteroviruses, and caliciviruses.

Bacteria

Bacterial infection is also a common cause of gastroenteritis. Examples include:

• Campylobacter jejuni - a common cause of food poisoning, especially from chicken.

• Escherichia coli (E. coli)ost strains of E. coli are harmless and are part of the normal bacteria that live in the gut, but some strains produce toxins which can cause illness.

• Salmonella bacteria.

• Shigellabacteria.

• Vibrio cholerae - bacteria that cause cholera. Cholera isn't found in the UK, but outbreaks do occur in developing countries. There is a vaccine for cholera for people who are at risk - for example, people travelling to areas where there is cholera.

• Clostridioides difficile (Clostridium difficile, or 'C. diff') - this can cause gastroenteritis in people who have recently had antibiotics, which can kill off 'good bacteria' in the gut.

Parasites

Parasites are a less common cause of gastroenteritis in the UK, but still affect some people. Examples include:

• Cryptosporidium - affects sheep and cattle, and can be passed on to humans. Sometimes it can be passed from human-to-human.

• Giardia lamblia.

• Entamoeba histolytica.

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Types of gastroenteritis

Gastroenteritis is usually divided up by the different infectious causes - for example, bacterial gastroenteritis, viral gastroenteritis, and parasitic gastroenteritis.

Another way to categorise gastroenteritis is by the length of symptoms:

• Acute gastroenteritis - symptoms last less than 14 days.

• Persistent, or prolonged, gastroenteritis - symptoms last 14 to 30 days.

• Chronic gastroenteritis - symptoms last longer than 30 days.

Acute gastroenteritis often doesn't need specific tests - persistent or chronic gastroenteritis may require further assessment to look for causes that need treatment.

Risk factors for gastroenteritis

Some groups of people are at particular risk of gastroenteritis. These include:

• Infants and young children, who have less-developed immune systems, but also tend to have close contact with other children - such as at nursery - who might spread gastroenteritis.

• Older adults, who may have weaker immune systems and also may be at risk of outbreaks if they live in residential or nursing homes.

• People who live in crowded areas.

• People who are travelling to countries where food and drink may be contaminated.

• People with weakened immune systems for other reasons - such as people having chemotherapy, or people with HIV/AIDS.

• People who have anal sex, including anal-oral sex.

• People taking acid-reducing medications for the stomach - proton-pump inhibitors or H2 receptor antagonists - seem to be at higher risk of getting gastroenteritis. This is probably because stomach acid protects against infections.

How do you catch gastroenteritis?

Gastroenteritis is spread by swallowing a virus, bacteria, or parasite which then goes on to cause infection in the gut. These organisms are usually spread in the vomit and poo (faeces) of people or animals with the infection. Getting even tiny traces of vomit or poo in the mouth can cause infections to spread from person to person.

Ways of catching gastroenteritis include:

• Eating or drinking contaminated food or water - food poisoning. This might happen because:

  • The person preparing the food or drink is unwell and has spread the infection by touching it. This is why people with gastroenteritis shouldn't prepare food for other people until they have recovered.

  • The food wasn't properly prepared - for example, meat was under-cooked, or not stored properly.

  • The water source is contaminated with an infection - this is unlikely in most developed countries, but can occur in countries where sanitation is poor. This is why you might be advised to drink only bottled or boiled water in some places.

• Person-to-person contact with someone who has the infection, such as:

  • Shaking hands with someone who has the infection on their hands and then later touching your mouth.

  • Anal sex - including touching the anus of someone with the infection, or oral-anal sex.

• Some infections can also be spread through droplets in the air, for example if someone vomits.

How to prevent gastroenteritis

Gastroenteritis is very contagious. Ways to prevent gastroenteritis involve stopping the chain of transmission.

Further reading

• Gastroenteritis; NICE CKS, June 2022 (UK access only).