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.

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:

  • diarrhea (loose stools)
  • nausea (feeling sick or queasy)
  • vomiting
  • abdominal pain (stomach cramps)

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:

  • loss of appetite
  • fever or high temperature and chills

Symptoms by type

The 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 malnutrition

One 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 gastroenteritis

Viral gastroenteritis is also called stomach flu.

Viruses that most commonly cause viral gastroenteritis are:

  • Rotavirus. More common in children and the most common cause of viral gastroenteritis in children
  • Norovirus. More common in adults

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 gastroenteritis

The 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 gastroenteritis

Parasites 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:

PathogenTime before symptoms startTime symptoms lastCommon food sources
Bacillus cereus10–16 hours24–48 hoursmeat, stew, gravy, vanilla sauce
Campylobacter jejuni2–5 days2–10 daysuncooked poultry, unpasteurized milk, water containing pathogens
E. coli1–3 days3–7 daysuncooked meat (usually beef), raw leafy green vegetables like lettuce, unpasteurized milk, water containing pathogens
Rotavirus 2 days3–8 daysany food containing pathogens from fecal matter
Norovirus12–48 hours1–3 daysraw oysters, fruit, and vegetables washed in dirty water
Cryptosporidium2–10 days1–2 weeksany food or water containing pathogens
Giardia1–2 weeks1–3 weeksany food or water containing pathogens

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:

  • drinking plenty of liquids (preferably with oral rehydration salts to replace lost electrolytes — see below)
  • ensuring fluid intake even if vomiting persists, by sipping small amounts of water or allowing ice cubes to melt in the mouth
  • gradually starting to eat again

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 gastroenteritis

Drugs 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 gastroenteritis

Probiotics (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:

  • Lactobacillus rhamnosus GG
  • Saccharomyces boulardii

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:

  • beef, chicken
  • fish (especially raw like sushi) and seafood like shellfish
  • fruit and vegetables
  • sprouts
  • raw flour
  • eggs

Standard advice to avoid food poisoning includes four key components:

  • Cook. Ensure adequate heating time at the proper temperature to kill any bacteria that could cause gastroenteritis. It is helpful to use a thermometer to test cooked meat and to ensure egg yolks are firm.
  • Separate. Separate foods to avoid cross-contamination and especially raw meat.
  • Chill. Chilled storage slows the growth of harmful bacteria.
  • Clean. Keep utensils and worktops clean and wash hands frequently, especially before eating or touching the mouth and after handling raw meat or eggs.

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.

Gastroenteritis causes gastrointestinal inflammation. This usually results in vomiting and diarrhea.

A common cause of gastroenteritis is foods that contain infectious microbes, in which case it is called food poisoning. Bacteria, viruses, and parasites are all pathogens that can commonly cause the condition.

Individuals should seek out medical care if they get lightheaded, have bloody diarrhea, fevers, are over 65, have multiple medical problems, are pregnant, or if symptoms do not get better in a few days.