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Food poisoning

Page last reviewed: 13/07/2011

Food poisoning is an illness caused by eating contaminated food. Most people will get better without the need for treatment. 

In most cases, the food that causes the illness has been contaminated by bacteria, such as salmonella, or a virus, such as the norovirus.

The symptoms of food poisoning usually begin one to three days after eating contaminated food. They include:

  • feeling sick
  • vomiting
  • diarrhoea
  • stomach cramps

Foods that are particularly vulnerable to contamination if they are not handled, stored or cooked properly include:

  • meat
  • 'ready to eat' food, such as pre-packed sandwiches
  • dairy products, such as eggs and milk

How common is food poisoning?

A North/South study showed that in 2010 there were 4,500 reported cases of food poisoning in the island of Ireland. However, the actual figure may be considerably higher than this because many people with mild symptoms do not report them.


Most people with food poisoning will get better without the need for treatment. In the meantime, you can relieve the symptoms of food poisoning by:

  • drinking plenty of fluids
  • eating easily digested food, such as toast, until you feel better
  • resting

Read more about treating food poisoning.

Occasionally, food poisoning can have more serious effects on a person's health, particularly if they are vulnerable to the effects of an infection. For example, being older than 65 or having a condition that weakens the immune system, such as HIV, can increase a person's chances of having a more severe reaction.

Signs that you may have a more serious case of food poisoning that requires medical attention include:

  • vomiting that lasts for more than two days
  • not being able to keep liquids down for more than a day
  • diarrhoea that lasts for more than three days

Read about the symptoms of food poisoning for more information on when to seek medical advice.

Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some others are good for you.

Page last reviewed: 13/07/2011

The time it takes for symptoms to develop after eating contaminated food ranges from one hour to 90 days.

Usually, symptoms of food poisoning develop after one to three days.

The most common symptoms are:

  • nausea
  • vomiting
  • diarrhoea

Other symptoms of food poisoning include:

  • stomach cramps
  • abdominal pain
  • loss of appetite
  • a high temperature of 38C (100.4F) or above
  • muscle pain
  • chills

When to seek medical advice

Most cases of food poisoning do not require medical attention. But contact your GP if you have any of the following:

  • vomiting that lasts for more than two days
  • you cannot keep liquids down for more than a day
  • diarrhoea that lasts for more than three days
  • blood in your vomit
  • blood in your stools
  • seizures (fits)
  • changes in mental state, such as confusion
  • double vision
  • slurred speech
  • signs that you may be severely dehydrated, such as a dry mouth, sunken eyes, and being unable to pass urine


Reporting cases of food poisoning

If you think your food poisoning has been caused by a restaurant or other food-related business, report it to your local environmental health department.

Environmental health officers will carry out an investigation and, if necessary, ensure that the business involved improves its standards of hygiene to prevent it happening ag


Always contact your GP if you develop food poisoning during pregnancy. Extra precautions may be needed to ensure the safety of both you and your baby.

Page last reviewed: 13/07/2011

Food can become contaminated at any stage during its production, processing or cooking.

For example, food poisoning can be caused by:

  • not cooking food at the right temperature and/or for the right length of time
  • not chilling food at the correct temperature
  • someone with unclean hands touching the food
  • eating the food after it has passed its 'use by' date
  • cross-contamination


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, harmful bacteria can be spread from the chopping board to the salad.

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

Sources of contamination

Food contamination is usually caused by bacteria. Some common types are described below as are viruses and toxins.


Campylobacter is the most common cause of food poisoning in Ireland. Campylobacter bacteria are usually found in raw meat and poultry, unpasteurised milk and untreated water.


Salmonella bacteria are often found in raw meat and poultry. They can also be passed into dairy products such as eggs and unpasteurised milk.


Listeria bacteria may be found in a range of chilled ready-to-eat food including:

  • pre-packed sandwiches
  • pâté
  • butter
  • soft cheeses, such as brie, camembert or others with a similar rind
  • soft blue cheese
  • cooked sliced meats
  • smoked salmon

Escherichia coli

Escherichia coli, known as E. coli, are bacteria found in the digestive system of many animals, including humans. Most strains are harmless but some strains can cause serious illness.

Some cases of E. coli food poisoning occur after eating undercooked beef or drinking unpasteurised milk.


Two viruses that commonly cause food poisoning are the rotavirus and the norovirus.

The rotavirus is more common in children than adults because most adults develop immunity (resistance) to it. Noroviruses can affect people of any age.

People infected with either virus can contaminate food if they do not wash their hands properly after going to the toilet and then handle food.


In Ireland, food poisoning from parasites is rare. It is much more common in the developing world.

Toxoplasmosis is the most likely cause of parasitical food poisoning in Ireland. It is caused by a parasite that is found in the digestive systems of many animals, particularly cats.

People can develop toxoplasmosis by consuming undercooked contaminated meat, or food or water contaminated with the faeces of infected cats.


There is a small risk that oily fish could be contaminated by toxins such as a chemical called polychlorinated biphenyls (PCBs).

The levels of toxins in contaminated fish are thought to be very low, but they could still pose a risk to unborn babies. Therefore pregnant women are advised not to eat more than two portions of oily fish a week.

Examples of oily fish include:

  • fresh tuna (not canned tuna, which does not count as oily fish)
  • mackerel
  • sardines
  • trout
  • salmon

Some fish contain a high level of mercury, which can also damage an unborn baby's nervous system. Therefore, pregnant women should avoid eating:

  • shark
  • swordfish
  • marlin
  • more than two tuna steaks a week (or four medium cans of tuna a week)


Page last reviewed: 13/07/2011

Most people with food poisoning will not need to see their GP.

Most cases of food poisoning do not require medical attention. But contact your GP if you have any of the following:

  • vomiting that lasts for more than two days
  • you cannot keep liquids down for more than a day
  • diarrhoea that lasts for more than three days
  • blood in your vomit
  • blood in your stools
  • seizures (fits)
  • changes in mental state, such as confusion
  • double vision
  • slurred speech
  • signs that you may be severely dehydrated, such as a dry mouth, sunken eyes, and being unable to pass urine

Usually, you only need to see your GP for a diagnosis if:

  • your symptoms are severe and are not getting better
  • you have symptoms of severe dehydration, such as sunken eyes and not being able to urinate
  • there has been an outbreak of similar cases of food poisoning linked to a possible source of contamination

Your GP will ask you about your symptoms and how you think you could have come into contact with contaminated food or liquid.

They will refer you for blood tests to check for infection. You may be asked to give a sample of your stools to test for bacteria or parasites.

Further testing is usually only required if you have symptoms that suggest the infection has spread from your digestive system to other parts of your body, such as your nervous system.


Page last reviewed: 13/07/2011

In most cases of food poisoning, you can relieve your symptoms at home without needing to see a doctor.

The most important thing is to make sure you don't become dehydrated, as this will make you feel worse and slow your recovery time.

Dehydration is a risk because fluid is lost through vomiting and diarrhoea.

Aim to drink at least two litres (3.5 pints) of water a day, as well as 200ml (one-third of a pint) of water every time you pass diarrhoea.

If you are more vulnerable to the effects of dehydration (for example, if you are elderly or already have a health condition), oral rehydration salts are recommended.

They are available in sachets from pharmacies. You dissolve them in water to drink and they help to replace salt, glucose and other important minerals that your body loses through dehydration.

If you have a kidney condition, some types of oral rehydration salts may not be suitable for you. Ask your pharmacist or GP for advice about this.

Here are some further ways to cope with your symptoms and speed up your recovery time:

  • eating smaller, more frequent meals is easier than trying to eat three large meals
  • stick to easily digested foods, such as toast, crackers, bananas and rice until you begin to feel better
  • avoid alcohol, cigarettes, caffeine and spicy and fatty foods because these will make you feel worse
  • rest 

When to see your GP

If you are showing signs of severe dehydration, such as sunken eyes and being unable to urinate, see your GP. They may admit you to hospital, so you can be given fluids and nutrients intravenously (through a tube placed directly into your vein). Read more information about treating dehydration.

Antibiotics can be prescribed if testing shows that the source of the food poisoning was bacterial and your symptoms are severe or last longer than three to four days.

Antibiotics tablets are usually used, although you may be given antibiotics injections if your symptoms are particularly severe or it is felt you would have problems keeping tablets down.


Page last reviewed: 13/07/2011

A useful way of preventing food poisoning is to remember the four Cs:

  • cleaning
  • cooking
  • chilling
  • cross-contamination


You can prevent the spread of harmful bacteria and viruses by having good personal hygiene and keeping all your work surfaces and utensils clean.

Wash your hands frequently with soap and warm water, particularly:

  • after going to the toilet
  • after handling raw food
  • before preparing food

Remember never to:

  • handle food when you are ill with stomach problems, such as diarrhoea or vomiting
  • touch food if you have sores and cuts (unless they are covered with a waterproof dressing)


It is always important to cook food thoroughly, particularly meat, as this will kill any harmful bacteria such as listeria and salmonella.

Make sure the food is cooked thoroughly and is piping hot in the middle. You can check that the meat is cooked by inserting a knife: if the juices that come out are clear and there is no pink/red meat left, it is fully cooked. Some meat, such as steaks and joints of beef or lamb, can be served rare (not cooked in the middle) as long as the outside has been cooked properly.

If you are reheating food, make sure it is piping hot all the way through. Do not reheat food more than once.


It is important to keep certain foods at the correct temperature to prevent harmful bacteria from growing and multiplying. Always check the label on the packaging.

If food has to be refrigerated, set your fridge to between zero and 5°C (32 and 41°F).

If food that needs to be chilled is left standing at room temperature, bacteria can grow and multiply to dangerous levels.

Cooked leftovers should be cooled quickly, ideally within one to two hours, and then put in your fridge or freezer. Putting food in shallow containers and dividing it into smaller amounts will speed up the cooling process.


Cross-contamination occurs when bacteria are transferred from foods (usually raw foods) to other foods. Contamination can be:

  • direct, where one food touches or drips onto another food
  • indirect, where bacteria on your hands, equipment, work surfaces or utensils are spread to food

To prevent cross-contamination:

  • Always wash your hands after handling raw food.
  • Keep raw and ready-to-eat foods separate.
  • Store raw meat in sealable containers at the bottom of your fridge, so that it cannot drip onto other foods.
  • Use a different chopping board for raw food and ready-to-eat food, or wash it well in between preparing different foods.
  • Clean knives and other utensils thoroughly after they have been used with raw food.
  • Never wash raw meat because this could splash harmful bacteria around the kitchen.


Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some others are good for you.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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