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About food poisoning
Food poisoning is an illness caused by eating contaminated food. It's not usually serious and most people get better within a few days without treatment.
In most cases of food poisoning, the food is contaminated by bacteria, such as salmonella or Escherichia coli (E. coli), or a virus, such as the norovirus.
Signs and symptoms
The symptoms of food poisoning usually begin within one to two days of eating contaminated food, although they may start at any point between a few hours and several weeks later.
The main symptoms include:
- feeling sick (nausea)
- diarrhoea, which may contain blood or mucus
- stomach cramps and abdominal pain
- a lack of energy and weakness
- loss of appetite
- a high temperature (fever)
- aching muscles
In most cases, these symptoms will pass in a few days and you will make a full recovery.
What to do
Most people with food poisoning recover at home and don't need any specific treatment, although there are some situations where you should see your GP for advice (see below).
Until you feel better, you should rest and drink fluids to prevent dehydration. Try to drink plenty of water, even if you can only sip it.
Eat when you feel up to it, but try small, light meals at first and stick to bland foods – such as toast, crackers, bananas and rice – until you begin to feel better.
Oral rehydration solutions (ORS), which are available from pharmacies, are recommended for more vulnerable people, such as the elderly and those with another health condition.
Read more about treating food poisoning
When to see your GP
You should contact your GP if:
- your symptoms are severe – for example, if you're unable to keep down any fluids because you are vomiting repeatedly
- your symptoms don't start to improve after a few days
- you have symptoms of severe dehydration, such as confusion, a rapid heartbeat, sunken eyes and passing little or no urine
- you're pregnant
- you're over 60
- your baby or young child has suspected food poisoning
- you have a long-term underlying condition, such as inflammatory bowel disease (IBD), heart valve disease, diabetes or kidney disease
- you have a weak immune system – for example, because of medication, cancer treatment or HIV
In these situations, your GP may send off a stool sample for analysis and prescribe antibiotics, or they may refer you to hospital so you can be looked after more closely.
How is food contaminated?
Food can become contaminated at any stage during production, processing or cooking. For example, it can be contaminated by:
- not cooking food thoroughly (particularly meat)
- not correctly storing food that needs to be chilled at below 5C
- leaving cooked food for too long at warm temperatures
- not sufficiently reheating previously cooked food
- someone who is ill or who has dirty hands touching the food
- eating food that has passed its "use by" date
- the spread of bacteria between contaminated foods (cross-contamination)
Foods particularly susceptible to contamination if not handled, stored or cooked properly include:
- raw meat and poultry
- raw eggs
- raw shellfish
- unpasteurised milk
- "ready-to-eat" foods, such as cooked sliced meats, pâté, soft cheeses and pre-packed sandwiches
Read more about the causes of food poisoning and preventing food poisoning
Causes of food poisoning
Food can become contaminated at any stage during its production, processing or cooking.
For example, it can become contaminated by:
- not cooking food thoroughly (particularly meat)
- not correctly storing food that needs to be chilled at below 5C
- keeping cooked food unrefrigerated for a long period
- eating food that has been touched by someone who is ill or has been in contact with someone with diarrhoea and vomiting
- cross-contamination (where harmful bacteria are spread between food, surfaces and equipment)
Cross-contamination can occur, for example, if you prepare raw chicken on a chopping board and don't wash the board before preparing food that won't be cooked (such as salad), as the harmful bacteria can be spread from the chopping board to the salad.
It can also occur if raw meat is stored above ready-to-eat meals and juices from the meat drip on to the food below.
See preventing food poisoning for information about reducing these risks
Types of infection
Food contamination is usually caused by bacteria, but it can also sometimes be caused by viruses or parasites. Some of the main sources of contamination are described below.
In the UK, campylobacter bacteria are the most common cause of food poisoning. The bacteria are usually found on raw or undercooked meat (particularly poultry), unpasteurised milk and untreated water.
The incubation period (the time between eating contaminated food and the start of symptoms) for food poisoning caused by campylobacter is usually between two and five days. The symptoms usually last less than a week.
Salmonella bacteria are often found in raw or undercooked meat, raw eggs, milk, and other dairy products.
The incubation period is usually between 12 and 72 hours. The symptoms usually last around four to seven days.
Listeria bacteria may be found in a range of chilled, "ready-to-eat" foods, including pre-packed sandwiches, cooked sliced meats and pâté, and soft cheeses (such as Brie or Camembert).
All of these foods should be eaten by their "use-by" dates. This is particularly important for pregnant women, because a listeria infection (known as listeriosis) in pregnancy can cause pregnancy and birth complications, and can result in miscarriage.
The incubation period can vary considerably, from a few days to several weeks. The symptoms will usually pass within three days.
Escherichia coli (E. coli)
Escherichia coli, often known as E. coli, are bacteria found in the digestive systems of many animals, including humans. Most strains are harmless but some can cause serious illness.
Most cases of E. coli food poisoning occur after eating undercooked beef (particularly mince, burgers and meatballs) or drinking unpasteurised milk.
The incubation period for food poisoning caused by E. coli is typically one to eight days. The symptoms usually last for a few days or weeks.
Shigella bacteria can contaminate any food that has been washed in contaminated water.
Symptoms typically develop within seven days of eating contaminated food and last for up to a week.
An infection caused by Shigella bacteria is known as bacillary dysentery or shigellosis. See the topic on dysentery for more information about it.
The virus that most commonly causes diarrhoea and vomiting is the norovirus. It's easily spread from person to person, through contaminated food or water. Raw shellfish, particularly oysters, can also be a source of infection.
The incubation period typically lasts 24-48 hours and the symptoms usually pass in a couple of days.
In young children, the rotavirus is a common cause of infection from contaminated food. The symptoms usually develop within a week and pass in around five to seven days.
In the UK, food poisoning caused by parasites is rare. It's much more common in the developing world.
Parasitic infections that can be spread in contaminated food include:
- giardiasis – an infection caused by a parasite called Giardia intestinalis
- cryptosporidiosis – an infection caused by a parasite called Cryptosporidium
- ameobiasis – a type of dysentery caused by a single-cell parasite (ameoba) called Entamoeba histolytica (this is very rare in the UK)
The symptoms of food poisoning caused by a parasite usually develop within 10 days of eating contaminated food, although sometimes it may be weeks before you feel unwell.
If left untreated, the symptoms can last a long time – sometimes several weeks or even a few months.
Treating food poisoning
Food poisoning can usually be treated at home without seeking medical advice. Most people will feel better within a few days.
It's important to avoid dehydration by drinking plenty of water, even if you can only sip it, as you need to replace any fluids lost through vomiting and diarrhoea.
You should also:
- rest as much as possible
- eat when you feel up to it – sticking to small, light and non-fatty meals at first (bland foods such as toast, crackers, rice and bananas are good choices)
- avoid alcohol, caffeine, fizzy drinks and spicy and fatty foods because they may make you feel worse
Contact your GP if your symptoms are severe or don't start to improve in a few days.
Preventing the spread of infection
If you have food poisoning, you shouldn't prepare food for other people and you should try to keep contact with vulnerable people, such as the elderly or very young, to a minimum.
Stay off work or school until at least 48 hours after the last episode of diarrhoea.
If someone you live with has food poisoning, you should:
- make sure everyone in your household (including yourself) washes their hands with soap and warm water regularly – particularly after going to the toilet and before and after preparing food
- clean surfaces, toilet seats, flush handles, basins and taps frequently
- make sure everyone has their own towels and flannels
- wash the laundry of the infected person on the hottest washing machine setting
Oral rehydration solution (ORS)
Oral rehydration solutions (ORS) are recommended for people vulnerable to the effects of dehydration, such as the elderly and those with a pre-existing health condition.
ORSs are available in sachets from pharmacies. You dissolve them in water to drink and they help replace salt, glucose and other important minerals 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 further advice about this.
If your symptoms are severe or persistent, or you are more vulnerable to serious infection (for example, because you are elderly or have an underlying health condition), you may need further treatment.
Tests may be carried out on a stool sample to find out what it causing your symptoms and antibiotics may be prescribed if the results show you have a bacterial infection.
Medication to stop you vomiting (anti-emetics) may also be prescribed if your vomiting is particularly severe.
In some cases, you may need to be admitted to hospital for a few days so you can be monitored and given fluids directly into a vein (intravenously).
Preventing food poisoning
The best way to avoid getting food poisoning is to ensure you maintain high standards of personal and food hygiene when storing, handling and preparing food.
The Food Standards Scotland (FSS) recommends remembering the "four Cs":
- cross-contamination (avoiding it)
It's also recommended that you stick to a food’s "use by" date and the storage instructions on the packet.
These steps are important because things such as a food's appearance and smell aren't a reliable way of telling if it's safe to eat.
You can prevent the spread of harmful bacteria and viruses by maintaining good personal hygiene standards and keeping work surfaces and utensils clean.
Regularly wash your hands with soap and warm water, particularly:
- after going to the toilet or changing a baby's nappy
- before preparing food
- after handling raw food
- after touching bins or pets
You shouldn't handle food if you are ill with stomach problems, such as diarrhoea or vomiting or you have any uncovered sores or cuts.
It's important to cook food thoroughly, particularly meat and most types of seafood, to kill any harmful bacteria that may be present.
Make sure the food is cooked thoroughly and is steaming hot in the middle. To check that meat is cooked, insert a knife into the thickest or deepest part. It is fully cooked if the juices are clear and there is no pink or red meat. 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.
When reheating food, make sure it is steaming hot all the way through. Don't reheat food more than once.
Certain foods need to be kept at the correct temperature to prevent harmful bacteria from growing and multiplying. Always check the storage instructions on the label.
If food has to be refrigerated, make sure your fridge is set to 0–5C (32–41F).
If food that needs to be chilled is left at room temperature, bacteria can grow and multiply to dangerous levels.
Cooked leftovers should be cooled quickly, ideally within a couple of hours, and put in your fridge or freezer.
Cross-contamination is when bacteria are transferred from foods (usually raw foods) to other foods.
This can occur when one food touches or drips onto another food, or when bacteria on your hands, work surfaces, equipment or utensils are spread to food.
To prevent cross-contamination:
- always wash your hands after handling raw food
- store raw and ready-to-eat foods separately
- 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 thoroughly in between preparing different types of food
- clean knives and other utensils thoroughly after using them with raw food
- do not wash raw meat or poultry – any harmful bacteria will be killed by thorough cooking, and washing may splash harmful bacteria around the kitchen
22 February 2023
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