Food can become contaminated at any stage during its production, processing or cooking. Show
For example, it can become contaminated by:
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 infectionFood 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. CampylobacterIn 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. SalmonellaSalmonella 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. ListeriaListeria 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. ShigellaShigella 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. VirusesThe 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. ParasitesIn 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:
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 Youssef (Joe) Soliman, MD — Written by Markus MacGill and Alina Sharon — Updated on June 21, 2022 Food poisoning is a major cause of gastroenteritis, resulting in a well-known set of unpleasant symptoms. Gastroenteritis generally resolves without medication, but in some cases, it can lead to complications. Share on PinterestTommaso Tuzj/Stocksy The Food and Drug Administration (FDA) cites that in spite of high standards in the U.S. food supply, about 48 million cases of foodborne illnesses occur annually due to eating food containing an infectious pathogen. There are also 128,000 hospitalizations and 3,000 deaths as a result of food poisoning. This article discusses the common symptoms, causes, and treatment of food poisoning. Gastroenteritis is a condition involving inflammation of the lining of the gut — in particular, of the stomach and intestines. It usually results from pathogens that infect a person and cause symptoms. These are usually viruses, bacteria, or parasites. When the source of such infection is food, it is called food poisoning. Gastroenteritis may also be referred to as “gastric flu” or “stomach flu.” The most common symptoms are usually diarrhea, nausea, vomiting, and abdominal pain. It can also lead to dehydration, especially in vulnerable people such as the very young and very old. The onset of gastroenteritis symptoms after eating food infected with a pathogen can be within a few hours, but the incubation period can also be much longer, depending on the pathogen involved. Four well-known, classic symptoms are typical:
These symptoms can occur in any combination. They generally have a sudden (acute) onset, but this, and symptom severity, can vary. Vomiting usually happens earlier on in the disease, diarrhea usually lasts for a few days, but can be longer depending on the organism that is causing the symptoms. In addition to the classic symptoms above, gastroenteritis can also bring about:
Symptoms by typeThe type of gastrointestinal symptoms is a clue to the type of infection. Viral infection generally produces diarrhea without blood or mucus and watery diarrhea is a prominent symptom. Conversely, a person is more likely to have diarrhea with mucus and blood in bacterial diarrhea. Norovirus can cause acute onset of vomiting, especially in children. Dehydration and malnutritionOne of the dangers of food poisoning and gastroenteritis — especially in very young, old, or otherwise vulnerable people — is the loss of fluids resulting from diarrhea and vomiting, which can lead to dehydration. Dehydration can, however, be prevented. In the case of parasitic gastroenteritis, another danger is malnutrition. The parasites reach the intestines and feed off the nutrients a person absorbs from their food. This results in a person developing a chronic lack of nutrients. Infections can pass from person to person when people spread a pathogen by touching food, especially in cases where hand hygiene is more challenging. There are generally viruses, bacteria, or parasites. Viral gastroenteritisViral gastroenteritis is also called stomach flu. Viruses that most commonly cause viral gastroenteritis are:
Less common viral causes are astrovirus, usually affecting children and the elderly, and adenoviruses. Cytomegalovirus can cause gastroenteritis, especially in people with compromised immunity. Bacterial gastroenteritisThe microorganisms that most commonly cause bacterial gastroenteritis are: A study from the U.S. Centers for Disease Control and Prevention (CDC)’s Interagency Food Safety Analytics Collaboration found that between 2015–2019, 75% of E. coli cases came from beef and leafy green vegetables. Parasitic gastroenteritisParasites are organisms that need to live inside and feed off other organisms in order to survive. Though gastroenteritis caused by parasites is more common in low and middle-income regions, parasitic infections do occur globally. About 450 million people become ill around the world annually. The two types of parasites that typically infect the human gastrointestinal tract are single-celled protozoa and helminths, which are worm parasites. Common protozoa infections include giardiasis and cryptosporidiosis. Learn about parasitic infections in humans. The time it takes for symptoms to appear may depend on the bacteria or pathogen causing the illness. Though different pathogens will affect the body in different ways, the FDA and CDC summarize how common pathogens might cause gastroenteritis as follows: Gastroenteritis and food poisoning usually resolve without any medical intervention. Treatment is focused on reducing the symptoms and preventing complications, especially dehydration. The main treatment and prevention strategy for food poisoning is to rest and replace lost fluids and electrolytes by:
What should a person eat?There are no specific restrictions on food, but blander foods might be easier to digest. These can include: A person may want to avoid fatty, sugary, or spicy foods, as well as dairy products, caffeine, and alcohol, as these may worsen symptoms. How to prevent dehydration?To avoid the dangerous and potentially fatal effects of dehydration from diarrhea, a person should drink oral rehydration salts (ORS). Research shows that using ORS has prevented more than 50 million deaths from diarrhea around the world since 2007. Since 1980 this use reduced the mortality from diarrhea in children under the age of 5 by about two-thirds. Dehydration has been a more significant risk in low or middle-income countries. In higher-income countries, while the threat of death is smaller, rehydration is nonetheless important. A person can replace salt, glucose, and minerals lost through dehydration through sachets of oral rehydration salts available from pharmacies and online. A person can dissolve the salts in drinking water and this does not require a doctor’s prescription. It is important to get the right concentration, as too much sugar can make diarrhea worse, while too much salt can be extremely harmful, especially for children. A more diluted solution (for instance using more than 1 liter of water), is preferable to a more concentrated solution. Store-bought products like Pedialyte and Gatorade also help restore electrolytes and increase hydration. Drug treatments for gastroenteritisDrugs are available to reduce the main symptoms of gastroenteritis, which are diarrhea and vomiting: Antidiarrheals are available over-the-counter, while antiemetics are available via a prescription. A person should speak with a doctor before taking anti-diarrhea medication as some infections may get worse with anti-diarrhea medicines. If a person’s stomach flu is caused by bacteria, they may also need to take antibiotics. Probiotics and gastroenteritisProbiotics (live “good” bacteria and yeasts) may also be helpful in treating gastroenteritis, according to some newer research. One study found that the use of probiotics in children hospitalized for acute gastroenteritis shortened the duration of diarrhea by a mean of 1.16 days. Specifically, there is some evidence to support the use of the following strains of beneficial bacteria in the treatment of gastroenteritis in children, alongside the use of oral rehydration solutions without dietary restriction:
This is a new area of study, so there may be more research about using probiotics to treat gastroenteritis in the future. People with compromised immunity are especially at risk of getting food poisoning and getting severe symptoms, as their bodies may not be able to fight off the infection as well. Other people at risk include people over the age of 65, pregnant people, children, and infants. In addition, a person who eats the following foods may be more at risk:
Standard advice to avoid food poisoning includes four key components:
Food poisoning is usually easy to diagnose from the symptoms alone with little need for confirmation from a doctor. The symptoms a patient reports are usually sufficient to inform a diagnosis. In some cases, stool testing is necessary. For example, if diarrhea is accompanied by blood or is watery for more than a few days, doctors may want a stool sample to test for parasites or bacteria. During an outbreak of rotavirus, for example, the doctor may request other specific tests. In some cases based on the patient’s symptoms or history, a doctor may rule out other conditions such as appendicitis, diverticulitis, or bowel obstruction. The following are answers to common questions about gastroenteritis. What are other causes of gastroenteritis?In rarer cases, a few other causes can lead to gastroenteritis. These include eating food containing heavy metals, and eosinophilic gastroenteritis, which is a sensitivity or allergy to certain foods. Sometimes, when a person eats food containing bacteria, they may not get sick from the bacteria itself but from a toxin that the bacteria releases. Is it food poisoning or stomach flu?Food poisoning refers to gastroenteritis caused by eating food containing pathogens. This can have a viral cause, such as norovirus for example, which is when it is referred to as “stomach flu.” However, this is not what people think of as the “flu,” which is the influenza virus. Learn more about stomach flu vs influenza. Is gastroenteritis contagious?Gastroenteritis is contagious. The degree of contagion can depend on the type of pathogen and the amount a person has been exposed to. It may also depend on any predisposing factors, such as whether the person is immunocompromised, for example. A person who is ill other people while they have symptoms and for several weeks after getting better. A person can pass the infection to someone else by touching water, food, or other objects infected with pathogens. They can also do it by coming in physical contact with another person or by breathing out droplets containing the pathogen. Learn more about contracting stomach flu. Last medically reviewed on June 21, 2022
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