Gastroenteritis - Causes 

Causes of gastroenteritis 

Gastroenteritis is an infection of the stomach and large intestine (bowel). The infection interferes with the absorption of water from the contents of your intestines into the body, which is one of the main functions of the intestines.

This is why watery diarrhoea is the most common symptom of gastroenteritis and why dehydration is a complication.

In England, the two most common causes of gastroenteritis in adults are a norovirus infection and bacterial food poisoning (see below). 


Noroviruses are the most common cause of viral gastroenteritis in adults. Norovirus infections are sometimes referred to as "winter vomiting bugs" because they tend to be more widespread during the winter months. However, they can occur at any time of the year.

Norovirus outbreaks often occur in confined environments, such as hospitals, nursing homes, schools and cruise ships. This is because the illness spreads very easily from person to person, and the virus can survive for several days in a contaminated area.

Noroviruses can be spread through coming into contact with an infected person or contaminated surfaces or objects, or by eating or drinking contaminated food or water.

There are many different types of norovirus and it is possible for you to get a norovirus infection several times. This is because after getting the illness, immunity to the virus only lasts for 14 weeks.

Read more about norovirus infections.

Food poisoning

Most cases of bacterial gastroenteritis are caused by food poisoning. Some cases of viral gastroenteritis can also be caused by food poisoning.

Food can become contaminated with a virus if it is handled by a person with a viral infection. Contamination can occur at any stage during the food's production, processing or cooking.

For example, food poisoning can be caused by:

  • not cooking food at the right temperature or for the right length of time
  • not chilling food at the correct temperature
  • someone who has not washed their hands properly handling the food 
  • eating food after it has reached its use by date
  • cross-contamination (see below)

Read more about food poisoning.


Cross-contamination is a cause of food poisoning that is often overlooked. It occurs when harmful bacteria are spread between food, surfaces and equipment.

For example, if you prepare raw chicken on a chopping board and do not wash the board before preparing a ready-to-eat meal, such as a salad or sandwiches, harmful bacteria can be spread from the chopping board to the ready-to-eat meal.

Cross-contamination can also occur if you store raw meat above ready-to-eat meals in the fridge. The meat juices may drip onto the meals and contaminate them.

The most common types of bacteria that are associated with gastroenteritis are:

  • campylobacter – a bacterium found in raw meat and poultry, unpasteurised milk and untreated water
  • salmonella – a bacterium found in raw meat, poultry, eggs and unpasteurised milk
  • escherichia coli (E. coli) – a bacterium found in undercooked beef and unpasteurised milk

Traveller's diarrhoea

Traveller's diarrhoea refers to gastroenteritis that develops after travelling abroad. It can be caused by a range of different bacteria or parasites such as:

  • the shigella bacterium or the entamoeba parasite – these are both spread through poor hygiene and cause a type of traveller's diarrhoea called dysentery
  • cryptosporidium – a parasite found in soil, food or water that has been contaminated with animal or human faeces
  • giardia intestinalis – a parasite found in water that has been contaminated with animal or human faeces (infections that are caused by this parasite are known as giardiasis)

Read more about traveller's diarrhoea

Page last reviewed: 10/05/2012

Next review due: 10/05/2014


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