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Food poisoning

Food poisoning occurs when you eat food contaminated with bacteria, viruses, parasites, or toxins. Symptoms include diarrhea, vomiting, and stomach cramps. Food poisoning generally starts 2 to 6 hours after eating contaminated food. Food poisoning is often caused by bacteria. However, it can also result from eating chemicals in poisonous plants (some mushrooms, for instance) and animals (puffer fish). Food poisoning is especially common during summer when food may not be kept cold enough to prevent bacteria from growing.


Signs and Symptoms

The typical signs of food poisoning are nausea, vomiting, abdominal cramping, diarrhea, head or muscle aches, and fever. Specific bacteria may cause these additional signs and symptoms:

  • Clostridium botulinum (C. botulinum, or botulism). Extreme dry mouth, constipation, retention of urine, weakness, blurred vision, sensitivity to light, double vision, paralyzed eye nerves, difficulty speaking and swallowing, and eventually paralysis that spreads downward, respiratory failure, and death.
  • Salmonella spp., Shigella spp., and Campylobacter jejuni (C. jejuni). Fever, chills, and bloody diarrhea.
  • Escherichia coli (E. coli). Hemorrhagic colitis (diarrhea with very little stool and large amounts of blood), occurring up to 3 days after eating contaminated food.
  • Mushroom poisoning. Delirium (confusion), vision difficulties, heart muscle problems, kidney failure, death of liver tissue, and death if left untreated.

Fish poisoning causes nausea, vomiting, diarrhea, abdominal pain, dizziness, and headache. Specific types of fish poisoning can cause other signs and symptoms, such as:

  • Ciguatera (caused by ciguatoxins in some coral reef fish, including sea bass, grouper, red snapper, kingfish, and barracuda). Numbness or tingling around the mouth, feeling of loose teeth, impaired touch sensation of hot as cold and cold as hot, itching, muscle and joint pain, slow heart rate, low blood pressure.
  • Numbness or tingling around the mouth, trouble coordinating movement, difficulty swallowing, excess saliva, twitching, loss of ability to talk, convulsions, paralysis that spreads upward, respiratory failure, and death (Pufferfish poisoning).
  • Numbness or tingling around the mouth or in the arms and legs, trouble swallowing, difficulty speaking (Shellfish poisoning, caused by toxins in algae that are eaten by shellfish).

What Causes It?

Usually bacteria and algae cause food poisoning. However, poisonous plants and animals are other potential causes.

Common bacterial causes include:

  • E. coli in undercooked hamburger, unpasteurized apple juice or cider, raw milk, contaminated water (or ice), vegetables fertilized by cow manure, or spread from person to person.
  • Listeria monocytogenes (L. monocytogenes) in cole slaw, dairy products (mostly soft cheeses from outside the United States), and cold, processed meats.
  • Salmonella spp. in poultry, beef, eggs, or dairy products.
  • Shigella spp. from raw vegetables or cool, moist foods (such as potato and egg salads) that are handled after cooking.
  • Staphylococcus aureus (S. aureus) in salad dressing, ham, eggs, custard-filled pastries, mayonnaise, and potato salad (usually from the hands of food handlers).
  • C. jejuni in raw milk and chicken.
  • C. botulinum in improperly home canned foods (in children under 1 year of age, mostly from honey but also from corn syrup).
  • Clostridium perfringens (C. perfringens) in meat and poultry dishes and gravies, mostly foods that were cooked more than 24 hours before eating and were not reheated well.
  • Vibrio cholerae in bivalve (two shelled) shellfish (such as mussels, clams, oysters, and scallops), raw shellfish, and crustaceans (such as lobsters, shrimp, and crabs).

Common types of fish poisoning include:

  • Scombroid poisoning from bacteria in dark meat fish (tuna, bonito, skipjack, mahi-mahi, mackerel) that are not refrigerated well.
  • Ciguatera poisoning in tropical fish (grouper, surgeonfish, snapper, barracuda, moray eel, shark) that have eaten toxic plankton.
  • Puffer fish poisoning from the organs and flesh of puffer fish (containing tetrodotoxin).
  • Poisoning from shellfish that feed on certain algae.

Mushroom poisoning occurs from eating poisonous wild mushrooms, especially Amanita phalloides.

Who's Most At Risk?

Infants and the elderly are at greater risk for food poisoning. Other risk factors include:

  • A weakened immune system, pregnant women, and people over age 65 are most at risk
  • A pre-existing medical condition, such as chronic kidney failure, liver disease, or diabetes
  • Traveling in an area where contamination is more likely

Listeriosis is common in pregnant women and people with immune problems. When a fetus is infected with listeria, it may be born prematurely or die.

What to Expect at Your Provider's Office

Your health care provider will examine you for signs and symptoms of food poisoning, such as stomach problems, neurologic problems, and dehydration.

Your health care provider may also ask about foods you have eaten recently, where you may have traveled, and if you have had contact with people showing similar symptoms.

Tests of your vomit, blood, and stool can sometimes identify the cause.

In the case of botulism, your health care provider may request serum and stool test (to confirm botulinum neurotoxin) and electromyography (a test to measure electric impulses in the muscles) to confirm the diagnosis.

Although brain imaging and lumbar puncture (spinal tap) results are normal in patients with botulism, they may be done to check for signs and symptoms related to central nervous system disorders.

Treatment Options


These steps can help prevent food poisoning:

  • Wash your hands and clean any dishes or utensils when you are making or serving food.
  • Keep juices from meat, poultry, and seafood away from ready-to-eat foods.
  • Cook foods to proper temperatures.
  • Refrigerate any food you will not be eating right away.
  • If you take care of young children, wash your hands often and dispose of diapers carefully so that bacteria can't spread to other surfaces or people.
  • If you make canned food at home, make sure to follow proper canning techniques to prevent botulism.
  • Do not feed honey to children under 1 year of age.
  • Do not eat wild mushrooms.
  • When traveling where contamination is more likely, eat only hot, freshly cooked food. Boil water before drinking. Do not eat raw vegetables or unpeeled fruit.
  • Always refrigerate fish.
  • Don't eat tropical fish caught during blooms of poison plankton.
  • Eat pufferfish only in specially licensed restaurants with chefs trained to cook it.
  • Don't eat shellfish exposed to red tides.

If others may have eaten a food that made you sick, let them know. If you think the food was contaminated when you bought it from a store or restaurant, tell the staff and your local health department.

Treatment Plan

Treatment for most cases of food poisoning involve replacing fluids and electrolytes (such as sodium, potassium, magnesium, and chloride). While experiencing vomiting and diarrhea, the person should avoid solid food but increase clear liquids. In more severe cases, a person may need help either breathing or stopping vomiting. Health care providers usually don't prescribe antibiotics because they may prolong diarrhea. If you have eaten certain toxins (such as from mushrooms or shellfish), your health care provider may take steps to clean out your stomach (a process called lavage, or pumping the stomach) and administer activated charcoal, which can help absorb the remaining toxin.

Drug Therapies

Depending on the symptoms, cause, and severity of food poisoning, a health care provider may prescribe drugs, including:

  • Oral rehydration therapy
  • Antibiotics
  • Antitoxin to neutralize toxins from C. botulinum (only given within the first 72 hours)
  • Amitriptyline to control the numbness and tingling from ciguatera poisoning
  • Apomorphine or ipecac syrup to cause vomiting and help rid the body of toxins
  • Atropine for mushroom (muscaria) poisoning
  • Diphenhydramine and cimetidine for fish poisoning
  • Mannitol for nerve-related symptoms of ciguatera poisoning

Complementary and Alternative Therapies

If you are suffering from severe food poisoning, seek conventional medical treatment. Complementary and alternative therapies are best used to strengthen the body and aid in the prevention of food poisoning.


The following general nutritional guidelines may be helpful in the case of food poisoning:

  • Drink plenty of fluids (to prevent dehydration).
  • While recovering, eat small meals of easily digestible food (soup, rice, bananas, toast, potatoes, apples)
  • Probiotics, such as Lactobacillus acidophilus and Lactobacillus bulgaricus, can help maintain or restore the balance of good bacteria in the intestine. If you are traveling to an area where the food and water may be contaminated, in addition to taking the precautions above, taking probiotics both before and during your trip may help maintain intestinal health. People with weakened immune systems should speak with their doctors before taking probiotics.
  • Several in vitro studies suggest that vinegar, as well as a number of cooking herbs (including thyme, rosemary, basil, coriander, sage, spearmint, and fennel) may have antimicrobial effects against food borne pathogens. However, no study demonstrates they can prevent or treat food poisoning in humans.

Various herbs have been used traditionally to treat different types of food poisoning. More research is needed. The following herbs should not be used in place of conventional medical care and are listed only for the purposes of discussion.

  • Milk thistle (Silybum marianum), its extract (silymarin), or active components (silybin or silibinin) have traditionally been used to treat liver disease. They have also been tested in people with Amanita mushroom poisoning, and reports showed success in some cases. Despite anecdotal evidence, human studies supporting the effectiveness of milk thistle for mushroom poisoning are still lacking. A few rigorous clinical studies have found no benefit of milk thistle in patients with liver disease. Side effects include allergic reactions and low blood sugar levels.

Animal studies of Chinese and Japanese combination herbal remedies used for Listeria suggest they may be effective for food poisoning. Active ingredients include Asian ginseng (Panax ginseng), Astragalus root (Astragalus membranaceus), Chinese cinnamon bark (Cinnamomum aromaticum), ginger root (Zingiber officinale), licorice (Glycyrrhiza glabra), peony root (Paeonia officinalis), or skullcap (Scutellaria lateriflora). No human studies have confirmed these effects. Do not take these herbs if you have high blood pressure, heart disease, or are taking blood-thinning medication (such as warfarin). Other drug interactions or dangerous side effects are possible, so make sure you discuss any herbal treatment with your provider.

Barberry (Berberis vulgaris) has been used traditionally to treat diarrhea from infectious causes such as E. coli and V. cholera. Berberine, the active ingredient in barberry, is also present in other plants (goldenseal, Oregon grape, and goldthread). Berberine can cause brain damage in newborns. Pregnant women should avoid berberine. Berberine may also lower blood sugar so patients with hypoglycemia or on diabetes medication should use caution. Other side effects are possible so speak to a physician before using berberine-containing herbs.


Studies examining the effectiveness of homeopathic remedies for food poisoning are lacking. Before prescribing a remedy, homeopaths take into account a person's constitutional type -- their physical, emotional, and intellectual makeup. Below are some more common remedies for food poisoning or diarrhea:

  • Arsenicum album
  • Chamomilla
  • Calcarea carbonica
  • Podophyllum
  • Sulphur

Prognosis/Possible Complications

Most cases of food poisoning are mild and clear up on their own within 4 to 7 days. However, with mushroom (especially Amanita) poisoning, serious complications may occur and liver transplantation may become necessary. If treated early, the mortality is about 5% to 10%. With botulism, less than 10% die, and some people may need help breathing for months afterward. Many poisonings from pufferfish are fatal, however global statistics are lacking. Death is rare in other fish poisonings, but nerve-related symptoms can continue for months.

The following are some possible after effects of food poisoning:

  • After shigellosis, white blood cell problems and kidney problems
  • After E. coli infection, kidney problems and bleeding problems
  • After botulism, long hospital stays (1 to 10 months) with fatigue and difficulty breathing for 1 to 2 years, or muscle weakness followed by respiratory failure
  • After salmonellosis, reactive arthritis or Reiter syndrome
  • After campylobacteriosis, Guillain-Barré syndrome (a nerve disease)

Following Up

For a severe case of food poisoning, you may need to stay in the hospital to receive fluids and electrolytes, so health care providers can monitor your breathing. Doctors may need to insert a tube down the throat (intubate) or connect you to a machine to help with breathing. Dialysis may be required. Cathartics (substances that help the body remove waste), enemas, and lavage may help eliminate toxins.

Supporting Research

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Review Date: 4/9/2018  

Reviewed By: Steven D. Ehrlich, NMD, Solutions Acupuncture, a private practice specializing in complementary and alternative medicine, Phoenix, AZ. Review provided by VeriMed Healthcare Network. Also reviewed by the A.D.A.M. Editorial team.

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