Food Poisoning


Food poisoning comes from eating food or drinking water that is contaminated with a virus, bacterium, parasite, or chemical that causes illness. It is also called gastroenteritis.


Foodborne illness is a serious public health concern in the United States and around the world. More than 250 foodborne diseases have been identified. Most food poisoning is unpleasant but not severe enough to require professional medical treatment. However, the economic impact of food poisoning is substantial.

The organisms and chemicals that cause food poisoning can contaminate food at any point during the production process. Animal products cause the majority of food poisonings. They can become contaminated during slaughter, processing, transport, storage, or preparation. A vegetarian diet, however, does not protect a person from food poisoning. Fruits and vegetables can be contaminated in the fields from animal feces or pesticides, as well as during harvesting, processing, distribution, and storage.

The CDC estimates that about 97% of all food poisoning comes from improper food handling. Of that, 80% occurs from food prepared in businesses (e.g., restaurants or work cafeterias) or institutions (e.g., schools or jails). The remaining 20% occurs from food prepared at home. In the twenty-first century, American bioterrorism experts have become increasingly concerned that a disease-causing organism could intentionally be introduced into the food or water supply to cause a mass outbreak of food poisoning illness.

Certain foods are more commonly associated with food poisoning than others. These include:

Risk factors

Although the food supply in the United States is probably the safest in the world, anyone can get food poisoning. Serious outbreaks are rare. When they occur, the very young, the eldery, and those with immune system weaknesses have the most severe and life-threatening symptoms. For example, these groups are 20 times more likely to become sick from Salmonella bacteria than the general population.

Travel outside the United States to countries where less attention is paid to sanitation, water purification, and good food-handling practices increases the chances that a person will get food poisoning. People living in institutions such as nursing homes are also more likely to get food poisoning.


The CDC estimates that food poisoning causes about 76 million cases of illness in the United States each year at a cost of between 5 and 6 billion dollars annually in direct medical care and lost productivity. The specific organism causing the disease is identified in only about 14 million cases. Most cases of food poisoning are mild, but about 325,000 individuals are hospitalized for food poisoning each year in the United States and about 5,000 die.

Internationally, food poisoning is about five times more common in developing countries than in the United States and Europe. In underdeveloped countries where contaminated water supplies are common and refrigeration is rare, foodborne illnesses may cause a billion illnesses and 4–6 million deaths each year.

Food poisoning is an equal-opportunity illness. It affects people independent of race, age, or gender. However, the very young, the elderly, pregnant women, and people with weakened immune systems (e.g., people with HIV/AIDS or leukemia or transplant patients) are more likely to have severe cases that result hospitalization and life-threatening complications.

Causes and symptoms

Food poisoning can be divided into two basic types: illness caused by infectious organisms and illness caused by chemicals. The infectious organisms (pathogens) that cause food poisoning are bacteria, viruses, and parasites. Chemicals can be either natural toxins (poisons) found in plants (e.g., poisonous mushrooms) and animals (e.g., Japanese puffer fish), or they can be manmade chemicals such as pesticides or herbicides.

Symptoms of food poisoning usually develop within 1–48 hours after eating contaminated food. Symptoms of chemical food poisoning often appear very quickly. The type of symptoms and their severity depend on the cause of the food poisoning, the amount of contaminated food eaten, and the health of the individual. Symptoms usually develop suddenly. Common symptoms of food poisoning include:


Bacteria of the genus Salmonella are common in reptiles, birds, and mammals. They are found most often in eggs, poultry, dairy products, and beef. The CDC estimates that in the United States, one out of every 50 consumers is exposed to contaminated egg yolk each year. However, thorough cooking kills the bacteria and makes the food harmless. Infection with Salmonella causes nausea, vomiting, stomach cramps, headache, and low-grade fever. Symptoms begin 6–48 hours after exposure and may last for 7 days. In people with weakened immune systems, Salmonella infection can be life-threatening.

Bacteria of the genus Campylobacter cause more diarrhea illnesses worldwide than any other group of bacteria. They produce fairly mild diarrhea, fever, and stomach cramps. Campylobacter bacteria are found in almost all raw chicken and turkey. Cross-contamination, that is putting cooked food down where raw food has been, is a leading cause of food poisoning from Campylobacter. These bacteria are also transmitted by water contaminated with animal feces.

Escherichia coli comprise a large group of bacteria, only some of which cause food poisoning. E. coli food poisoning usually begins with watery diarrhea that later turns bloody. One strain of E. coli, known as 0157:H7, is most often found in undercooked hamburger but has also been found in ready-to-eat raw spinach. This particular strain can cause kidney failure and death, especially in children and the elderly.

Clostridium botulinum causes both adult botulism and infant botulism. It is associated with improperly canned food, smoked fish, and honey and is unlike any of the other foodborne bacteria. First, C. botulinum is an anaerobic bacterium, which means that it can only live in the absence of oxygen. Second, the toxins from C. botulinum are neurotoxins. They poison the nervous system, causing paralysis without the vomiting and diarrhea associated with other foodborne illnesses. Third, toxins that cause adult botulism are released when the bacteria grow in an airless environment outside the body. They can be broken down and made harmless by heat. Finally, botulism is much more likely to be fatal even in tiny quantities.

Adult botulism outbreaks are usually associated with home canned food, although occasionally commercially canned or vacuum-packed foods are the source of the infection. C. botulinum grows well in nonacidic, oxygen-free environments. If food is canned at too low heat or for too brief a time, the bacteria are not killed. They reproduce inside the can or jar, releasing neurotoxin. The toxin can be made harmless by heating the contaminated food to boiling for ten minutes. However, even a very small amount of the C. botulinum toxin can cause serious illness or death.

Symptoms of adult botulism appear about 18–36 hours after the contaminated food is eaten, although onset can range from four hours to eight days. Initially a person suffering from botulism feels weakness and dizziness followed by double vision. Symptoms progress to difficulty speaking and swallowing. Paralysis moves down the body, and when the respiratory muscles are paralyzed, death results from asphyxiation. People who show any signs of botulism poisoning must receive immediate emergency medical care to increase their chance of survival.

Infant botulism was first recognized in 1976. It differs from adult foodborne botulism in its causes and symptoms. Infant botulism occurs when a child under the age of one year ingests the spores of C. botulinum. These spores are found in soil, but a more common source of spores is honey.

The C. botulinum spores lodge in the baby's intestinal tract and begin to grow, producing a neurotoxin. Onset of symptoms is gradual. Initially the baby is constipated. This is followed by poor feeding, lethargy, weakness, drooling, and a distinctive wailing cry. Eventually, the baby loses the ability to control its head muscles. From there, the paralysis progresses to the rest of the body.

Shigella is a common cause of diarrhea in travelers to developing countries. It is associated with contaminated food and water, crowded living conditions, and poor sanitation and sewage treatment. It is especially common after natural disasters (e.g., earthquake, flood, or hurricane) disrupt water and sewage treatment facilities. The bacterial toxins affect the small intestine.

Symptoms of food poisoning by Shigella appear 36–72 hours after eating contaminated food or drinking contaminated water. These symptoms are slightly different from those associated with most foodborne bacteria. In addition to the familiar watery diarrhea, nausea, vomiting, abdominal cramps, chills and fever occur. Diarrhea may be quite severe with cramps progressing to classical dysentery.


A large group of viruses called Norwalk or Norwalk-like viruses are an extremely common cause of foodborne illness. In the mid-2000s, Norwalk viruses were often in the news for causing outbreaks of gastrointestinal disease on cruise ships and in nursing homes. They cause more vomiting than diarrhea. Unlike many of the other causes of food poisoning, these viruses usually are not naturally present in food. They often are transferred from the hands of infected food handlers to the food that they are preparing, especially to foods such as salads and sandwiches.


Parasites that cause food poisoning usually come from contaminated water. They often cause mild symptoms that are slow to develop but last for several weeks. Giardia causes watery diarrhea and is often acquired by drinking untreated water from lakes or streams. Cryptosporidium is a parasite that causes large amounts of watery diarrhea for 3–4 days. Healthy people usually recover quickly, but in people with weakened immune systems, symptoms can persist for a long time.

Natural toxins

Natural poisons found in some wild mushrooms can cause anything from nausea and vomiting to hallucinations, coma, and death, depending on the amount and species of mushroom eaten. Mushroom poisoning is a medical emergency. People who believe they have eaten a poisonous mushroom should, if possible, take a sample of the mushroom or their vomit to the emergency room with them. Identifying the type of mushroom causing the illness can help determine the most effective treatment.

Oysters, clams, mollusks, and scallops can contain toxins that affect the nervous system. Symptoms usually begin with a tingling in the mouth then the arms and legs. Individuals may become dizzy and may have difficulty breathing. Shellfish poisoning is a medical emergency because the muscles needed for breathing may become paralyzed. Similar symptoms result from eating the Japanese puffer fish, which contains a natural poison in its skin and digestive system that affects the nervous system.

Manmade toxins

Manmade toxins include all pesticides, fertilizers, disinfectants, and all other chemicals remaining in food when it is eaten that can cause illness. Contamination is accidental and often the result of ignorance or a misunderstanding of how to apply the chemical. Symptoms may develop rapidly or slowly depending on the type of chemical and the amount of exposure. Chemical poisoning requires prompt medical evaluation.


Alice Catherine Evans was born on January 29, 1881, in Neath, Pennsylvania. Evans was the second of two children born to Anne Evans and William Howell. Evans taught grade school for four years because she could not afford to pay college tuition, and at that time a college degree was not required to teach young children. Following her time as a teacher, Evans enrolled at the Cornell University College of Agriculture, earning her B.S. degree. Evans' professor recommended her for a scholarship, which she received, and she began her master's degree program at the University of Wisconsin from which she graduated in 1910.

In 1911, instead of continuing her education, Evans took a position with the University of Wisconsin's Dairy Division as a researcher studying cheese making. In 1913, she moved to Washington, DC, with the division and worked with a team on identifying the cause of contamination in raw cow's milk. By 1917, Evans' research had shown that the bacteria responsible for undulant (Malta) fever was similar to one found when a cow experienced a spontaneous abortion. When administered to guinea pigs, the two bacteria produced similar results. Her findings were met with much skepticism but, as time went on, Evans' research began to gain support. She continued to document cases of the disease and to argue for the pasteurization process. Finally, after 1930, officials responsible for public health and safety realized the need for this process, which ultimately became a standard procedure. Evans retired from her position with the National Institute of Health in 1945 and died on September 5, 1975.



The main goal of treatment for food poisoning is to keep the individual from becoming dehydrated. A loss of 20% of a person's body fluid is fatal, and 10-15% is serious. In food poisoning, huge amounts of both water and electrolytes can be lost quite rapidly. Vomiting and diarrhea in infants and young children require especially prompt professional treatment because small children can become dehydrated within hours.

Mild cases of food poisoning usually can be treated at home, especially if they are not accompanied by a fever. Dehydration in infants and children can be prevented or treated by giving them oral rehydration solutions such as Pedialyte, Infalyte, Naturalyte, Oralyte, or Rehydralyte. These are available in supermarkets and pharmacies without a prescription. Oral rehydration solutions have the proper balance of salts and sugars to restore fluid and electrolyte balance. They can be given to young children in small sips as soon as vomiting and diarrhea start. Children may continue to vomit and have diarrhea, but some of the fluid will be absorbed. In the past, parents were told to withhold solid food from children who have diarrhea. Later research indicated that it is better for children to eat solid food should they want it, even though diarrhea continues.

Older children and adults who are dehydrated can be given oral rehydration solutions or sports drinks such as Gatorade. Adults and older children with food poisoning should avoid drinking coffee, tea, and soft drinks, especially soft drinks that contain caffeine, as these liquids promote dehydration. Over-the-counter medications to stop or slow diarrhea such as Kaopectate, Pepto-Bismol, or Imodium will not shorten the duration of the disease but may give individuals some control over their bowels. A physician should be consulted before giving these over-the-counter medicines to children.

Individuals of all ages who are seriously dehydrated need to be treated promptly by a medical professional. In the case of severe dehydration, the individual may be hospitalized and fluids given intravenously (directly into the vein). Drugs may also be prescribed to stop persistent vomiting. Although bacteria cause many cases of food poisoning, antibiotics are not routinely used in treatment. Some studies have shown that antibiotics are necessary only in about 10% of cases.

Salts and minerals that produce electrically charged particles (ions) in body fluids. Common human electrolytes are sodium chloride, potassium, calcium, and sodium bicarbonate. Electrolytes control the fluid balance of the body and are important in muscle contraction, energy generation, and almost all major biochemical reactions in the body.
An organism that causes a disease.
A general term for something that harms or poisons the body.

Individuals who think their food poisoning symptoms are caused by chemicals or natural toxins should seek emergency medical care immediately. These types of food poisoning are too serious to try to treat at home. When chemical or natural toxin poisoning is suspected, determining the exact cause is more important, and treatment is specific to the cause. The stomach may be pumped and the contents tested. Extensive blood tests are usually needed. Sometimes activated charcoal is used to help absorb the poison in the stomach.

Public health role and response

Contamination that causes food poisoning can occur at every level of the food production process, thus multiple public health agencies are involved in protecting the public. Some examples follow.

Although the food in the United States is safe, occasionally major outbreaks of food poisoning occur that can be traced to a breakdown in the food handling system. Larger outbreaks can be identified and traced to their source because each state has a list of diseases that health professionals are required to report to the county public health service once positive diagnosis is made. Most states require that doctors and hospitals report confirmed cases of disease caused by Salmonella and E. coli 0157:H7 and several other food poisoning pathogens. This information is then passed on to the CDC.

Most food poisoning occurs to single individuals or to a small group of people, such as a family at a picnic. A major food poisoning outbreak is suspected when many people develop the same symptoms of food poisoning within a short time or within the same geographic area. A major outbreak sets off a full investigation by a team of microbiologists, food scientists, process engineers, specialists in food sanitation, and others. In a larger outbreak, the CDC usually coordinates the investigation. The CDC has established a special system called FoodNet to monitor food poisoning reports and look for patterns that suggest an outbreak. Information on chemical and natural toxin poisonings is also collected by the American Association of Poison Control Centers.


Most people have unpleasant gastrointestinal symptoms—vomiting and diarrhea—for a few days and then recover fully from food poisoning. In young children, dehydration is always a cause for concern. Worldwide, dehydration from diarrhea is the biggest killer of children under age five. If dehydration can be controlled in young children with food poisoning, most recover with few complications. However, E, coli 0157:H7 can cause fatal renal failure in 3–5% of children. This bacteria is most often acquired by eating unpasteurized apple cider or apple juice, alfalfa or bean sprouts, or undercooked hamburger.


More serious long-term health problems often result from chemical poisonings. Toxins found in some wild mushrooms and some fish can cause permanent liver damage requiring a liver transplant or causing death. Pesticides and other chemical contamination can cause liver damage, kidney failure, and nervous system complications. In 2007, chemical contamination of pet food from China caused the death of hundreds of dogs and cats in the United States.


Appropriate food handling procedures at every level of the production process can go a long way in preventing food poisoning. Growers should apply only approved pesticides and herbicides at levels recommended by the Environmental Protection Agency and the Department of Agriculture. Processors must use clean sources of water to wash produce. Processing machinery must be disinfected regularly, and pesticides used in processing plants must be safe for use around food. In restaurants, food must not be held under warming lights of on buffet tables for long periods.

At home, individuals can help prevent food poison by following these guidelines.

See also Bioterrorism ; Chemical poisoning ; Dysentery ; Escherichia coli ; Foodborne illness ; Neurtoxin ; Parasites ; Sanitation ; Viruses .



Bjorklund, Ruth. Food Borne Illnesses. New York: Marshall Cavendish Benchmark, 2006.

Knechtges, Paul L. Food Safety: Theory and Practice. Sudbury, MA: Jones & Bartlett Learning, 2012.

Nestle, Marion. Safe Food: The Politics of Food Safety. Berkeley: University of California Press, 2010.


“Bacteria and Foodborne Illness.” National Digestive Diseases Information Clearinghouse. (accessed June 24, 2012).

Centers for Disease Control and Prevention. “Food Safety at CDC.” (accessed June 24, 2012).

“Foodborne Illness.” MedlinePlus. May 24, 2012. (accessed June 24, 2012).

Gammara, Roberto. “Food Poisoning.” . view (accessed June 24, 2012).


Food Standards Agency, Aviation House, 125 Kingsway, London, UK, WC2B 6NH, .

National Digestive Diseases Information Clearinghouse (NDDIC), 2 Information Way, Bethesda, MD, 20892-3570, (800) 891-5389; TTY (866) 569-1162, Fax: (703) 738-4929,, .

U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Rd., Atlanta, GA, 30333, (404) 639-3534, (800) CDC-INFO (232-4636). TTY: (888) 232-6348,, .

U.S. Department of Agriculture, 1400 Independence Ave. SW, Rm. 1180, Washington, DC, 20250, (202) 720-2791, .

U.S. Food and Drug Administration (FDA), 5600 Fishers Lane, Rockville, MD, 20857, (800) INFO-FDA (463-6332), .

World Health Organization, Avenue Appia 20, 1211 Geneva 27, Switzerland, 22 41 791 21 11, Fax: 22 41 791 31 11,, .

Tish Davidson, AM

  This information is not a tool for self-diagnosis or a substitute for professional care.