Food poisoning

What is food poisoning?

Food poisoning means becoming unwell from eating food or having a drink that is contaminated by germs or toxins.

Many types of germs can cause food poisoning, including bacteria, viruses and parasites. Common culprits are listed further down this page.

Food poisoning symptoms

• The main symptom is sudden onset diarrhoea, often with being sick (vomiting) as well. Diarrhoea is defined as "loose or watery stools (faeces), usually at least three times in 24 hours". Blood or mucus can appear in the stools with some infections.

• Crampy pains in your tummy (abdomen) are common. Pains may ease for a while after you pass some diarrhoea.

• You may feel hot one minute and cold and shivery the next. These are symptoms of a high temperature (fever) which sometimes develops along with the tummy symptoms.

• General symptoms of being unwell such as having no energy and no appetite.

The vomiting and diarrhoea usually start hours or a few days after eating the infected food or drink . If vomiting occurs, it often lasts only a day or so but can last longer. Diarrhoea often continues after the vomiting stops and may last for several days or more. Slightly loose stools may persist for a week or more before a normal pattern returns.

Symptoms of lack of fluid in the body

Diarrhoea and vomiting may cause lack of fluid in the body (dehydration). Mild dehydration is common and is usually easily reversed by drinking lots of water. Severe dehydration can be fatal unless quickly treated because the organs of your body need a certain amount of fluid to function. Consult a doctor if you suspect you are becoming dehydrated.

Symptoms of dehydration in adults include:

• Tiredness.

• Dizziness or light-headedness.

• Headache.

• Muscle cramps.

• Sunken eyes.

• Passing less urine.

• A dry mouth and tongue.

• Weakness.

• Becoming irritable.

Symptoms of severe dehydration in adults include:

• Profound loss of energy or enthusiasm (apathy).

• Weakness.

• Confusion.

• A fast heart rate.

• Producing very little urine.

• Coma - may occur.

Severe dehydration is a medical emergency and immediate medical attention is needed.

Dehydration in adults is more likely to occur in:

• Elderly or frail people.

• Pregnant women.

• People with severe diarrhoea and vomiting. In particular, if you are not able to replace the fluid lost with enough drinks.

Certain medications need to be temporarily stopped whilst a person has diarrhoea, vomiting or dehydration. This is because these medications can damage your kidneys if you are dehydrated. The medications should then be restarted once you have been eating and drinking normally for 24-48 hours. These are known as "sick day rules". These medications include some high blood pressure and diabetes medications as well as anti-inflammatory medicine. If you develop symptoms of food poisoning and are on regular medication then read the patient information leaflet inside the medication packet or speak to your pharmacist for advice. For more information see the reference "Sick Day card NHS Scotland" within the "Further reading" section below.

When do I need to seek medical advice for food poisoning?

You should seek medical advice if:

• You think that you are becoming dehydrated.

• You are vomiting and can't keep fluids down at all.

• You have blood in your stools (poo) or you vomit blood.

• You have severe tummy pain.

• You have severe symptoms, or if you feel that your condition is becoming worse.

• You have a high temperature (fever), which doesn't settle with medicines such as paracetamol, or which hangs about for three days or more.

• Your symptoms are not settling; for example, vomiting for more than a few days, or diarrhoea that does not start to settle after 3-4 days.

• Your infection was caught abroad.

• You are elderly or have an underlying health problem such as diabetes, epilepsy, inflammatory bowel disease, kidney disease.

• You have a weakened immune system because of, for example, chemotherapy treatment, long-term steroid treatment or HIV infection which is not well controlled.

• You are pregnant.

• You suspect that you may have contracted food poisoning from eating restaurant or takeaway food.

• There are any other symptoms that you are concerned about.

What causes food poisoning?

Food poisoning is common and most of us will experience it at some point. Causes of food poisoning include bacteria, toxins and parasites.

Bacteria

Campylobacter is the most common germ (bacterium) that causes food poisoning in the UK. Other germs (bacteria) that can cause food poisoning include:

• Salmonella.

• Escherichia coli (usually shortened to E. coli).

• Listeria.

• Shigella.

• Clostridium perfringens.

Viruses

Some germs (viruses), such as norovirus or rotavirus, can contaminate food and cause food poisoning.

Parasites

Parasites are living organisms that live within, or on, another organism. Examples include cryptosporidium, Entamoeba histolytica and giardia parasites. Food poisoning caused by parasites is more common in the developing world.

In the UK, a common cause of food poisoning is Toxoplasma gondii. This is a parasite that lives in the bowels of a number of animals, including cats. Food poisoning can occur if food or water is contaminated with the stools (faeces) of infected cats, or if raw or undercooked meat from an animal carrying the parasite is eaten.

The infection is known as toxoplasmosis. Symptoms of this type of food poisoning include swollen lymph glands and sometimes a skin rash. If you are pregnant and suspect you have caught toxoplasmosis it is important that you tell your doctor or midwife.

Toxins and chemicals

Poisons (toxins) produced by bacteria can also contaminate food, as well as the bacteria themselves. For example, the bacterium Staphylococcus aureus can contaminate ice cream and its toxins can lead to food poisoning. The bacterium Bacillus cereus can contaminate rice. If contaminated rice is reheated and eaten, the toxins produced can lead to food poisoning.

How does food become contaminated?

Contamination of food can occur during food production, storage or cooking. For example:

• Not storing food correctly or at the correct temperature. For example, not refrigerating food. This is particularly a problem for meat and dairy products.

• Inadequate cooking of food (undercooking or not cooking to the correct temperature). Bacteria are often found in raw meat, including poultry. Adequate cooking usually kills the bacteria.

• Contamination by someone preparing the food who has not followed food hygiene rules. This may include not washing their hands properly.

• Contamination from other foods (cross-contamination). For example, not washing a board used to prepare raw meat before you cut a slice of bread using the same board. Storing raw meat in the fridge above food that is 'ready-to-eat' and so allowing raw meat juices to drip on to the food below.

• Bacteria can also be present in unpasteurised milk and cheese. The pasteurisation process kills the bacteria.

How does water become contaminated?

Water can become contaminated with bacteria or other microbes usually because human or animal stools (faeces) get into the water supply. This is particularly a problem in countries with poor sanitation. In such countries, food may also be washed and prepared using contaminated water. So, for example, in countries with poor sanitation, you should always avoid:

• Drinking tap water.

• Having ice cubes in drinks (as the ice may have been made from contaminated water).

• Brushing your teeth with tap water.

• Eating salads (as the lettuce, tomatoes, etc, may have been washed in contaminated water).

• Eating uncooked vegetables (as they may have been washed in contaminated water).

How is food poisoning diagnosed?

Most people will recognise food poisoning from their typical symptoms. If symptoms are mild, you do not usually need to seek medical advice or receive specific medical treatment.

A phone call may be enough to reassure the doctor that you can safely stay at home and manage your condition with fluids and rest, or they may want to see you face to face, in which case the doctor or other healthcare professional will usually check you for signs of lack of body fluid (dehydration).

They may check your temperature, pulse and blood pressure. They may also examine your tummy (abdomen) to look for any tenderness.

Your doctor may ask you to collect a stool sample. This can then be examined in the laboratory to look for the cause of the infection. Your doctor is likely to suggest a stool sample if:

• If you have recently been abroad.

• If you are very unwell.

• If you have blood or pus in your stools.

• If your diarrhoea is not settling after a week.

• If you have recently been in hospital or had antibiotic treatment.

• If you have another medical condition, particularly one which affects your immune system.

• If the doctor is not sure you have food poisoning or a gut infection (gastroenteritis).

• If your job involves handling food.

The reason a stool sample is not always needed is that in many cases knowing what germ you have does not make any difference to the treatment you need. Most cases of food poisoning get better on their own even before the test result is back.

If you think your infection may have come from food at a particular restaurant or shop then inform your local Environmental Health Office. (Find them via the Food Standards Agency website's Report a food problem page.) This is so that the business can be checked out by environmental health officers.

How to treat food poisoning

Symptoms usually settle within a few days or so as your immune system clears the infection. Occasionally, admission to hospital is needed if symptoms are severe, or if complications develop (see below).

The following are commonly advised until symptoms improve:

Fluids - have lots to drink

The aim is to prevent lack of body fluid (dehydration). If you suspect that you are dehydrated, you should contact a doctor.

• As a rough guide, drink at least 200 mls after each watery stool (each bout of diarrhoea).

• This extra fluid is in addition to what you would normally drink. For example, an adult will normally drink about two litres a day but more in hot countries. The above '200 mls after each watery stool' is in addition to this usual amount that you would drink.

• If you are sick (vomit), wait 5-10 minutes and then start drinking again but more slowly. For example, a sip every 2-3 minutes and making sure that your total intake is as described above.

• You will need to drink even more if you are dehydrated. A doctor will advise how much.

It is best to drink mainly water. In addition you can try diluted fruit juice or thin soups. It is best to avoid very sugary or caffeinated drinks, as these can cause further dehydration.

Rehydration drinks are usually only recommended for the elderly or those with underlying health problems. They are made from sachets that you can buy from pharmacies. You add the contents of the sachet to water.

Rehydration drinks provide a good balance of water, salts, and sugar. The small amount of sugar and salt helps the water to be absorbed better from the gut (intestines) into the body. They do not stop or reduce diarrhoea. Do not use home-made salt/sugar drinks, as the quantity of salt and sugar has to be exact.

Eat small amounts if possible

It is advised to eat small, light meals if you can. Be guided by your appetite. Eat as soon as you are able - but don't stop drinking. If you do feel like eating, avoid fatty, spicy or heavy food. Plain foods such as bread and rice are good foods to try eating first.

Medication

Antidiarrhoeal medicines are not usually necessary. Your body is doing its best to get rid of the germ for you, and you will recover more quickly if you let it do so. However, a medicine called loperamide may be advised in some specific situations. Always speak to a pharmacist before taking this.

Paracetamol is useful to ease a high temperature, mild headache or mild abdominal discomfort.

In some cases, your doctor may ask for a sample of the diarrhoea. This is sent to the laboratory to look for infecting germs (microbes such as bacteria, parasites, etc). A course of antibiotic medicine may be used if a bacteria is identified. Examples where antibiotics might be needed include

• If symptoms are very severe.

• If the infection is not improving as expected. For example, if symptoms are still persisting after one week.

• If you are older than 50 with confirmed infection with salmonella.

• If you have other medical conditions, such as problems with your heart valves, and have confirmed salmonella infection.

• If you have blood in your diarrhoea and have confirmed shigella infection.

• If your immune system is not working as well as normal - for example, due to chemotherapy or if you have an illness such as AIDS.

• Infections with some specific germs, usually those acquired abroad. For example, infection with giardia, or amoebic infection.

What are the complications of food poisoning?

Complications are uncommon in the UK. Those who are older or have chronic health conditions are more likely to develop complications. Possible complications include the following:

• Salt (electrolyte) imbalance and lack of fluid (dehydration) in your body. This is the most common complication. It occurs if the salts and water that are lost in your stools (faeces), or when you are sick (vomit), are not replaced by drinking adequate fluids. If you can manage to drink plenty of fluids then dehydration is unlikely to occur, or is only likely to be mild, and will soon recover as you drink. People who are elderly or pregnant are more at risk of dehydration. If you are dehydrated you should seek urgent medical attention.

• Reactive complications. Rarely, other parts of your body can 'react' to an infection that occurs in your bowels. This can cause symptoms such as joint inflammation (arthritis), skin inflammation and eye inflammation (either conjunctivitis or uveitis).

• Spread of infection to other parts of your body such as your bones, joints, or the meninges that surround your brain and spinal cord. This is rare. If it does occur, it is more likely if diarrhoea is caused by salmonella infection.

• Persistent diarrhoea syndromes may rarely develop:

  • Irritable bowel syndrome is sometimes triggered by a bout of food poisoning.

  • Lactose intolerance can sometimes occur for a period of time after food poisoning. This is known as 'secondary' or 'acquired' lactose intolerance. Your bowel (intestinal) lining can be damaged by an episode of bowel infection. This leads to lack of a chemical (enzyme) called lactase that is needed to help your body digest a sugar called lactose that is in milk. Lactose intolerance leads to bloating, tummy (abdominal) pain, wind and watery stools after drinking milk or eating dairy products. The condition gets better when the infection is over and the bowel lining heals. It is more common in children than in adults.

• Haemolytic uraemic syndrome is another potential complication. It is rare and is usually associated with food poisoning caused by a certain type of E. coli infection. If recognised and treated, most people recover well.

• Guillain-Barré syndrome may rarely be triggered by campylobacter infection. This is a condition that affects the nerves throughout your body and limbs, causing weakness and sensory problems.

• Reduced effectiveness of some medicines. During an episode of food poisoning, certain medicines that you may be taking for other conditions or reasons may not be as effective. This is because the diarrhoea and/or vomiting means that reduced amounts of the medicines are taken up (absorbed) into your body. Examples of such medicines are those for epilepsy, diabetes and contraception. Speak with your doctor or practice nurse if you are unsure of what to do if you are taking other medicines and have food poisoning.

How to prevent food poisoning

The Foods Standards Agency in the UK has identified the '4 Cs' to help prevent food poisoning. These focus on:

• Cleanliness.

• Cooking.

• Chilling.

• Cross-contamination.

More information can be found using the link to the Food Standards Agency below.

Preventing the spread of food poisoning

Some infections causing diarrhoea and vomiting are very easily passed on from person to person. The following are recommended to prevent the spread of infection to others:

• Wash your hands thoroughly after going to the toilet. Ideally, use liquid soap in warm running water but any soap is better than none. Dry properly after washing.

• Don't share towels and flannels.

• Don't prepare or serve food for others.

• Regularly clean the toilets that you use. Wipe the flush handle, toilet seat, bathroom taps, surfaces and door handles with hot water and detergent at least once a day. Keep a cloth just for cleaning the toilet (or use a disposable one each time).

• Avoid social settings including work or school, until you have had no symptoms for 48 hours.

• Food handlers: if you work with food and develop diarrhoea or vomiting, you must immediately leave the food-handling area. For most, no other measures are needed, other than staying away from work until at least 48 hours after the last episode of diarrhoea or vomiting.

• If the cause of food poisoning is known to be (or suspected to be) a you should not swim in swimming pools for two weeks after the last episode of diarrhoea.