What is food poisoning?

Food poisoning occurs when food or water contaminated with harmful microbes (germs), toxins or chemicals is eaten or drunk. When we think of food poisoning, we usually think of the typical gastroenteritis - an infection of the gut (intestines) - which usually causes diarrhoea with or without vomiting. However, sometimes other symptoms or problems (such as nausea and abdominal cramping pain) can arise from eating contaminated food. Food poisoning can be caused by:

Bacteria

Campylobacter is the most common bacteria that causes food poisoning in the UK. Other bacteria that can cause food poisoning include salmonella, Escherichia coli (usually shortened to E. coli), listeria, shigella and Clostridium perfringens.

Viruses

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

Parasites

These are another type of microbe (germ). Examples include cryptosporidium, Entamoeba histolytica and giardia parasites. Food poisoning caused by parasites is more common in the developing world.

In the UK, the most common parasite that can cause food poisoning is toxoplasma. This is a parasite that lives in the gut of a number of animals, including cats. Food poisoning can occur if food or water is contaminated with the faeces of infected cats, or if raw or undercooked meat from another 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.

Toxins (poisons) and chemicals

Toxins can be produced by bacteria that contaminate the food. 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.

This is a general leaflet about food poisoning. There are separate leaflets that give more details about some of the different microbes that cause food poisoning.

How does food become contaminated?

Contamination of food can occur because of problems in 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 hot enough). Bacteria are often found in raw meat and poultry. Adequate cooking usually kills the bacteria.
• Contamination by someone preparing the food who has not followed food hygiene rules and has not washed 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 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, your child should always avoid drinking tap water, having ice cubes in drinks, and eating salads or uncooked vegetables.

How common is food poisoning?

It is common. The Food Standards Agency estimates that up to 5.5 million people in the UK are affected by food poisoning each year. Most people have only mild symptoms so the number of cases reported in the UK is less than 100,000 each year.

How long does it take for food poisoning to develop?

For most cases of food poisoning, symptoms tend to come on within one to three days of eating the contaminated food. However, for some types of food poisoning, this incubation period can be as long as 90 days.

What are the usual symptoms of food poisoning?

• The main symptom is diarrhoea, often with 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 child's abdomen (tummy) are common. Pains may ease for a while each time some diarrhoea is passed.
• A high temperature (fever), headache and aching limbs sometimes occur.
• If vomiting occurs, it often lasts only a day or so, but sometimes longer. Diarrhoea often continues after the vomiting stops and commonly lasts for several days or more. Slightly loose stools may persist for a week or so further before a normal pattern returns. Sometimes the symptoms last longer.

Symptoms of dehydration

Diarrhoea and vomiting may cause dehydration (a lack of fluid in the body). If you suspect your child may be becoming dehydrated then you should seek medical advice urgently. Children, especially young children, infants and babies, can become severely dehydrated and very ill very quickly. Mild dehydration is common and is usually easily reversed by drinking lots of fluids.

• Symptoms of dehydration in children include: passing little urine, a dry mouth, a dry tongue and lips, fewer tears when crying, sunken eyes, weakness, being irritable or lethargic.
• Symptoms of severe dehydration in children include: drowsiness, pale or mottled skin, cold hands or feet, very few wet nappies, fast (but often shallow) breathing. Severe dehydration is a medical emergency and immediate medical attention is needed.

Dehydration is more likely to occur in:

• Babies under the age of one year (and particularly those under six months old). This is because babies don't need to lose much fluid to lose a significant proportion of their total body fluid.
• Babies under the age of one year who were a low birthweight and who have not caught up with their weight.
• A breast-fed baby that has stopped breast-feeding during their illness.
• Any baby or child who does not drink much when they have gastroenteritis.
• Any baby or child with severe diarrhoea and vomiting (particularly if they have passed six or more diarrhoeal stools and/or vomited three or more times in the previous 24 hours).

How is food poisoning diagnosed and are tests required?

Most people will recognise food poisoning from their typical symptoms. If symptoms are mild, you do not usually need to seek medical advice or give your child any specific medical treatment apart from making sure they have lots to drink.

However, it is very important to seek urgent medical advice if your child is unwell, especially if they are becoming dehydrated. The doctor may ask you questions about recent travel abroad or any ways that your child may have eaten or drunk contaminated food or water. The doctor will also usually check your child for signs of dehydration.

Your doctor may ask for a stool sample to be collected and sent to a laboratory. This can then be examined in the laboratory to look for the cause of the infection. If your child is very unwell, they may need admission to hospital. If this is the case, further investigations may be needed such as blood tests, scans or a lumbar puncture. This is to look for spread of the infection to other parts of the body.

When should I seek medical advice?

Most children who have gastroenteritis due to food poisoning have mild symptoms which will get better in a few days. The important thing is to ensure that they have plenty to drink. In many cases, you do not need to seek medical advice.

However, you should seek medical advice in the following situations (or if there are any other symptoms that you are concerned about):

• If your child is under the age of six months.
• If your child has an underlying medical condition (for example, heart or kidney problems, diabetes, history of premature birth).
• If your child has a fever (high temperature).
• If you suspect dehydration is developing (see earlier).
• If your child appears drowsy or confused.
• If your child is vomiting and unable to keep fluids down.
• If there is blood in their diarrhoea or vomit.
• If your child has severe abdominal pain.
• Infections caught abroad.
• If your child has severe symptoms, or if you feel that their condition is getting worse.
• If your child's symptoms are not settling (for example, vomiting for more than 1-2 days, or diarrhoea that does not start to settle after 3-4 days).

Reporting the food poisoning episode

Any suspected case of food poisoning from eating takeaway or restaurant food should be reported to the local Environmental Health Office. This is so that the business can be investigated by environmental health officers. Further actions may be taken if there is a problem with their food hygiene practices. It is hoped that this will help to reduce the chance that other people will get food poisoning. You can find your local food standards enforcer using this link: www.food.gov.uk/enforcement/enforceessential/yourarea/.

If your doctor suspects or confirms that your child has food poisoning, they are also required by law to report this.

What is the treatment for food poisoning?

Symptoms of gastroenteritis often settle within a few days or so as a child's immune system is usually able to clear the infection. Children can usually be treated at home. Occasionally, admission to hospital is needed if symptoms are severe, or if complications develop.

Fluids to prevent dehydration

You should encourage your child to take plenty of fluids. The aim is to prevent dehydration (low body fluid). The fluid lost in their vomit and/or diarrhoea needs to be replaced. Your child should continue with their normal diet and usual drinks. In addition, they should also be encouraged to drink extra fluids. However, avoid fruit juices or fizzy drinks, as these can make diarrhoea worse.

Babies under six months old are at increased risk of dehydration. You should seek medical advice if they develop gastroenteritis. Breast-feeds or bottle-feeds should be encouraged as normal. You may find that your baby's demand for feeds increases. You may also be advised to give extra fluids (either water or rehydration drinks) in between feeds.

Rehydration drinks may be advised by a doctor for children at increased risk of dehydration (see above for who this may be). They are made from sachets available from pharmacies and on prescription. You should be given instructions about how much to give. Rehydration drinks provide a perfect balance of water, salts, and sugar. The small amount of sugar and salt helps the water to be absorbed better from the gut into the body. Do not use home-made salt/sugar drinks, as the quantity of salt and sugar has to be exact.

If your child vomits, wait 5-10 minutes and then start giving drinks again, but more slowly (for example, a spoonful every 2-3 minutes). Use of a syringe can help in younger children who may not be able to take sips.

Note: if you suspect that your child is dehydrated, or is becoming dehydrated, you should seek medical advice urgently.

Fluids to treat dehydration

If your child is mildly dehydrated, this may be treated by giving them rehydration drinks. Your doctor or nurse will advise about how to make up the drinks and about how much to give. The amount can depend on the age and the weight of your child. If you are breast-feeding, you should continue with this during this time. Otherwise, don't give your child any other drinks unless the doctor or nurse has said that this is OK. It is important that your child is rehydrated before they have any solid food.

Sometimes a child may need to be admitted to hospital for treatment if they are dehydrated. Treatment in hospital usually involves giving rehydration solution via a special tube called a nasogastric tube. This tube passes through your child's nose, down their throat and directly into their stomach. An alternative treatment is with intravenous fluids (fluids given directly into a vein).

Eat as normally as possible once any dehydration has been treated

Correcting any dehydration is the first priority. However, if your child is not dehydrated (most cases), or once any dehydration has been corrected, then encourage your child to have their normal diet. Do not starve a child with gastroenteritis. This used to be advised but is now known to be wrong. So:

• Breast-fed babies should continue to be breast-fed if they will take it. This will usually be in addition to extra rehydration drinks (described above).
• Bottle-fed babies should be fed with their normal full-strength feeds if they will take it. Again, this will usually be in addition to extra rehydration drinks (described above).
• Older children - offer them some food every now and then. However, if he or she does not want to eat, that is fine. Drinks are the most important, and food can wait until their appetite returns.

Medication is not usually needed

You should not give medicines to stop diarrhoea to children under 12 years old. They sound attractive remedies, but are unsafe to give to children, due to possible serious complications. However, you can give paracetamol or ibuprofen to ease a high temperature or headache.

If symptoms are severe, or persist for several days or more, a doctor may ask for a sample of the diarrhoea. This is sent to the laboratory to look for infecting germs (bacteria, parasites, etc). Sometimes an antibiotic or other treatments are needed, depending on the cause of the infection.

Stop the spread of infection to others

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

• Wash 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.
• Regularly clean the toilets that are used. 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).
• Stay off school until 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 germ called cryptosporidium, your child should not swim in swimming pools for two weeks after the last episode of diarrhoea.

Are there any complications that can occur from food poisoning?

Complications are uncommon in the UK but are more common in young children or children with long-term illness. Possible complications include the following:

• Dehydration and salt (electrolyte) imbalance. This is the most common complication. It occurs if the water and salts that are lost in your child's stools or vomit are not replaced by them drinking enough fluids. If your child can drink plenty of fluids then dehydration is unlikely to occur, or is only likely to be mild and will soon recover. Severe dehydration needs admission to hospital so that a 'drip' can be used to give fluid directly into a vein.
• Reactive complications. Rarely, other parts of the body can 'react' to an infection that occurs in the gut. This can cause symptoms such as arthritis (joint inflammation), skin inflammation and eye inflammation (either conjunctivitis or uveitis).
• Spread of infection to other parts of your child's body such as bones, joints, or the meninges that surround their brain and spinal cord. This is rare. If it does occur, it is more likely if diarrhoea is caused by salmonella infection.
• Persistent diarrhoeal 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 child's gut lining can be damaged by the episode of gut infection. This leads to lack of an enzyme (chemical) called lactase that is needed to help digest a sugar called lactose that is in milk. Lactose intolerance leads to bloating, abdominal pain, wind and watery stools after drinking milk. The condition gets better when the infection is over and the gut lining heals. It is more common in children than adults.
• Haemolytic uraemic syndrome is rare and is usually associated with food poisoning caused by a certain type of E. coli infection (E. coli O157). It is a serious condition where there is anaemia, a low platelet count in the blood, and kidney failure. It is more common in children than in adults. If it is recognised and treated early then most children recover well.
• Malnutrition may follow some gut infections. This is very unlikely with food poisoning and is a much greater risk for children in developing countries.
• Reduced effectiveness of some medicines. During an episode of food poisoning, certain medicines that your child may be taking for other conditions, such as epilepsy, may not be as effective. This is because the diarrhoea and/or vomiting means that reduced amounts of the medicines are absorbed (taken up) into your child's body.

Can food poisoning be prevented?

The Foods Standards Agency in the UK have identified the '4 Cs' to help prevent food poisoning:

Cleanliness

• Keep work surfaces and utensils clean.
• Wash and dry hands regularly but especially after going to the toilet, before preparing food, after handling raw food and before touching ready-to-eat food.
• Don't prepare food for others if you have diarrhoea or vomiting
• Cover any sores or cuts on hands with a waterproof plaster before you touch food.
• Change dishcloths and tea towels regularly.

Cooking

• Make sure that you cook food thoroughly, especially meat. This will kill bacteria. Food should be cooked right through and be piping hot in the middle.
• If you are reheating food, it needs to be cooked right through and be piping hot in the middle.
• Don't reheat food more than once.

Chilling

• Food that needs to be chilled or refrigerated should be. If food is left out of the fridge, bacteria may multiply to levels that can cause food poisoning.
• Your fridge needs to be kept between 0°C and 5°C. Also, don't leave the door open unnecessarily.
• Cool leftover food quickly and then refrigerate. Taking it out of the cooking pot and putting it into a shallow container can speed the cooling process up.

Cross-contamination

This is when bacteria pass from foods (commonly, raw foods) to other foods. It can occur if foods touch directly, if one food drips on to another, if your hands or utensils or equipment such as knives or chopping boards touch one food and then another.

• Wash your hands after touching raw foods.
• Separate raw and cooked or ready-to-eat foods.
• Keep raw meat in a sealable container at the bottom of the fridge.
• Don't use the same surface or chopping board for preparing raw and ready-to-eat foods.
• Make sure that knives and utensils are cleaned after preparing raw foods.

Special precautions may also be needed to prevent food poisoning if you are travelling abroad - see separate leaflet called 'Travellers' Diarrhoea' for further details. For example, avoid water and other drinks that may not be safe, and avoid food washed in unsafe water.