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.
Campylobacter
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
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
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
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.
Viruses
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.
Parasites
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.
Medically reviewed by Kevin Martinez, M.D. — Written by Brian Krans — Updated on January 24, 2022
Share on PinterestOksanaKiian/Getty Images
We include products we think are useful for our readers. If you buy through links on this page, we may earn a small commission. Here’s our process.
Food poisoning typically occurs when pathogens contaminate food or drinking water. Though uncomfortable, food poisoning is relatively common.
The Centers for Disease Control and Prevention (CDC) estimates that 1 in 6 people in the United States will get some type of food poisoning each year.
Let your stomach settle. After you experience the most explosive symptoms of food poisoning, like vomiting, diarrhea, and upset stomach, experts recommend letting your stomach rest. That means avoiding food and drink altogether for a few hours.
Stay hydrated
Liquid intake is crucial for helping your body fight off food poisoning effects. Vomiting and diarrhea can cause dehydration, so sucking on ice chips or taking small sips of water is a good starting point.
Sports drinks that contain electrolytes are the best way to prevent dehydration during this time. Other suggested liquids include:
- non-caffeinated sodas, such as Sprite, 7UP, or ginger ale
- decaffeinated tea
- chicken or vegetable broth
Eat bland food
When you feel you might be able to hold down food, eat foods that are gentle on your stomach and gastrointestinal tract. Stick to bland, low fat, low fiber foods. Fat is harder for your stomach to digest, especially when it’s upset. Avoid fatty foods to prevent upsetting it further.
Foods that are gentle on the stomach include:
The BRAT diet is a good guide to follow when you have food poisoning.
Try natural remedies
During an episode of food poisoning, it’s important for your body to follow its natural reaction to cleanse and purge the digestive tract to get rid of the harmful bacteria. That’s why an over-the-counter (OTC) diarrhea medication isn’t a good way to treat food poisoning.
While your symptoms are at their peak, you might want to try drinking ginger tea, as ginger is known to soothe the stomach.
Shop for ginger tea online.
Once you’re feeling well, you may wish to replace your normal intestinal flora with natural yogurts or probiotic capsules for at least 2 weeks.
Shop for probiotic capsules online.
This will help your body regenerate the healthy bacteria lost in the food poisoning purge and get your digestive system and immune system back on track.
Other tips
Delay brushing your teeth for at least an hour. Stomach acid expelled during vomiting can damage the enamel on your teeth, and brushing your teeth right after you vomit can further erode the enamel. Instead, rinse your mouth with a mix of water and baking soda.
Showering helps cleanse your body of the unhealthy bacteria. You should also be sure to get plenty of rest. Getting sufficient rest can help make you feel better faster.
Your body is already on the offensive, shooing away the pathogens responsible for food poisoning. You don’t want to give the invaders any more ammunition.
Your priority should be to avoid the foods that caused you to get sick in the first place. Throw the suspected culprit into the garbage immediately, and keep it shut so the contaminated food is out of your pets’ reach.
Avoid foods, drinks, and substances that are tough on the stomach, such as:
- alcohol
- caffeine, which is contained in beverages such as soda, energy drinks, or coffee
- spicy foods
- foods high in fiber
- dairy products
- fatty foods
- fried foods
- nicotine
- seasoned foods
- fruit juices
Also, remember to avoid any oral OTC diarrhea medications.
Follow these simple tips, and you should be feeling better soon.
Five pathogens are responsible for most foodborne illnesses in the United States. These pathogens are:
- norovirus, commonly found in oysters, fruits, and vegetables
- Salmonella, commonly found in eggs, meat, and dairy products
- Clostridium perfringens, found in meat and poultry
- Campylobacter, found in undercooked meat and contaminated water
- Staphylococcus, found in animal products, such as cream, eggs, and milk
Salmonella and norovirus are responsible for most hospitalizations for food poisoning. But hospitalizations for food poisoning can also be caused by the following:
- bacteria
- parasites
- mold
- toxins
- contaminants
- allergens
Undercooked meat and improperly handled produce are common culprits in food poisoning. Wash your hands, utensils, and plates between raw and cooked stages.
Most people who experience food poisoning don’t require a trip to the hospital, but you won’t want to venture too far from the bathroom either.
Upset stomach, vomiting, and diarrhea are the most common symptoms. They typically subside after 48 hours. If you have a history of dehydration, heart disease, embolism, or other serious health problems, seek help and drink plenty of fluids.
Call the Poison Help Line at 800-222-1222 if you experience severe symptoms. They track cases to help prevent outbreaks and can help determine if you should go to the hospital.
Severe symptoms of food poisoning include:
- blood in your stool
- severe abdominal cramping
- blurry vision
- diarrhea that lasts more than 3 days
These are all indications to seek medical care.
Read on to find out the right things to eat to recover quickly, and how else to know if you need to see a doctor.
Food poisoning is as common in children as it is in adults, and it can be cause for concern. Children, especially those under 1 year of age, are susceptible to botulism. Botulism is rare, but it can lead to paralysis and even death if not caught early.
Children are also in greater danger of having serious reactions to the E. coli bacteria.
Any infant or child that appears to have symptoms of food poisoning needs to be seen by a medical professional to rule out botulism and dehydration. Children become dehydrated more easily than adults and need to be monitored closely.
Pregnant people
Pregnant people should treat any case of food poisoning with caution. Listeria food poisoning has been shown to hurt the development of unborn babies.
Proper nutrition in pregnant people is essential to helping their babies develop. For this reason, any signs of food poisoning should be brought to the attention of a medical professional.
Older adults
Older adults are also more susceptible to complications from food poisoning. In particular, certain strains of E. coli can lead to hemorrhaging and kidney failure. If an adult over 65 has symptoms of food poisoning, they should contact their primary care physician for advice.
People with chronic conditions
People who have chronic illnesses such as HIV, liver disease, or diabetes are at a greater risk of experiencing more serious complications of food poisoning. Those receiving treatments that suppress the immune response, such as chemotherapy, are also at greater risk.
The symptoms of food poisoning don’t typically last more than 48 hours. If diarrhea lasts longer than 3 days, it’s time to call a medical professional.
Remember that severe symptoms, such as bloody stool, dizziness, muscle weakness, and severe stomach cramping should be taken seriously. Don’t wait for those symptoms to subside before seeing a doctor.
Last medically reviewed on January 24, 2022