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Gastroenteritis is a condition involving inflammation of the lining of the gut – in particular, of the stomach and intestines. It generally resolves without medication, but, in some cases, it can lead to complications.

Food poisoning is a major cause of gastroenteritis, resulting in a well-known set of unpleasant symptoms.

Gastroenteritis is usually caused by viruses, bacteria, or parasites; when the source of such infection is contaminated food, it is called food poisoning. Gastroenteritis may also be referred to as “gastric flu” or “stomach flu.”

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Drinking plenty of liquids can help treat dehydration.

Gastroenteritis and food poisoning usually resolve themselves 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. No specific restrictions are recommended, but blander foods might be easier to start with (cereal, rice, toast, and bananas are good examples).

The following may worsen symptoms during gastroenteritis episodes: fatty, sugary, or spicy foods, dairy products, caffeine, and alcohol.

To avoid the dangerous and potentially fatal effects of dehydration from diarrhea, oral rehydration salts (ORS) are recommended for vulnerable people (for example, infants and children, adults over 65 years of age, and people with weakened immunity).

Use of ORS in developing countries has been “one of the great public health success stories of our time,” according to a former director-general of the World Health Organization (WHO), Dr. Gro Harlem Brundtland – it reduced the number of deaths every year among children with acute diarrhea, from 5 million to 1.3 million deaths.

In developed countries, while the threat of death is smaller, rehydration is nonetheless important.

Salt, glucose, and minerals lost through dehydration are replaced by sachets of oral rehydration salts available from pharmacies and online. The salts are dissolved in drinking water and do 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 dilute 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 – diarrhea and vomiting:

  • Antidiarrheal medication such as loperamide (branded versions include Imodium, and Imotil, among others) and bismuth subsalicylate (for example, Pepto-Bismol)
  • Antiemetic (anti-vomiting) medication such as chlorpromazine and metoclopramide

Antidiarrheals are available OTC, while the antiemetics are available from doctors

Talk to a doctor before taking anti-diarrhea medication as some infections may get worse with anti-diarrhea medicines.

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 their hospital stay by an average of 1.12 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.

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Abdominal cramps can be a symptom of gastroenteritis.

Four well-known, classic symptoms are typical of gastroenteritis:

  • 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.

The onset of symptoms after eating contaminated food can be within a few hours, but the incubation period can also be much longer, depending on the pathogen involved.

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, food poisoning and gastroenteritis can also bring about:

  • Loss of appetite
  • Fever or high temperature and chills

The type of gastrointestinal symptoms are a clue to the type of infection – viral infection generally produces diarrhea without blood or mucus, and watery diarrhea is the prominent symptom. Conversely, mucus and blood are more often seen in bacterial diarrhea. Norovirus can cause acute onset of vomiting, especially in children.

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.

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.

Food poisoning and stomach flu have similar symptoms, but stomach flu is always caused by a virus, for example, the norovirus.

The time taken for symptoms to appear depends on the bacteria or pathogen involved.

According to the United States Food and Drug Administration (FDA):

  • Bacillus cereus: Present in meats, stews, and gravies, it takes 10 to 16 hours to trigger symptoms, and they last for 24 to 48 hours.
  • Campylobacter jejuni: Present in undercooked poultry, symptoms appear after 2 to 5 days and last for 2 to 10 days.
  • E. coli O157:H7: Present in undercooked beef, contaminated water, and others, symptoms appear after 1 to 8 days and last 5 to 10 days.

Different pathogens will affect the body in different ways. More details can be found on the FDA website.

The United States 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 because of contaminated food.

The FDA estimate that 128,000 hospitalizations and 3,000 deaths result from food poisoning.

The organization has produced a complete list of the microorganisms responsible for these illnesses along with a description of the symptoms each of these infections typically produces.

In broad terms, there are three types of infectious agents that cause gastroenteritis:

  • viruses
  • bacteria
  • parasites

The viruses that are most commonly implicated in 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.

The bacteria that are most commonly implicated in gastroenteritis are:

  • Salmonella
  • Campylobacter
  • Shigella
  • Escherichia coli (especially serotype O157:H7)
  • Clostridium difficile

A study from the U.S. Centers for Disease Control and Prevention’s Interagency Food Safety Analytics Collaboration found that from 2008 to 2012, 46 percent of E. coli cases came from beef, 18 percent of salmonella cases came from seeded vegetables, and 66 percent of campylobacter cases came from dairy products.

Gastroenteritis is usually easy to diagnose from the symptoms alone with little need for confirmation from a doctor; symptoms reported by the patient 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 sample to test for parasites or bacteria.

During an outbreak of, for example, rotavirus, specific tests may also be requested.

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Kitchen hygiene is the key to preventing food poisoning.

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.