Food Contamination


Food contamination occurs when potentially harmful substances render food unsafe for consumption. Microorganisms—viruses, bacteria, and parasites—are the most common food contaminants. Naturally occurring or manmade chemicals can also contaminate food.


Although widespread contamination is relatively rare in the United States, food contamination remains a serious public health concern throughout the world. In 2011, the U.S. Centers for Disease Control and Prevention (CDC) reported that about 48 million Americans—one in six—suffer the effects of food contamination every year, accounting for 128,000 hospitalizations and 3,000 deaths annually.

While disease-causing microorganisms are by far the most common contaminants in food, naturally occurring toxins sometimes contaminate shellfish and other organisms. Food also can be contaminated with heavy metals, manmade chemicals such as pesticides and herbicides, and radioactive iodine and cesium from nuclear accidents, such as the 2011 Fukushima Daiichi nuclear power plant disaster in Japan.

Farmers spraying pesticide in wheat field.

Farmers spraying pesticide in wheat field.

Although most food contamination is unintentional, sometimes contaminants are introduced as a means of “stretching” or extending the life of a product. In addition, bioterrorism experts worry that disease-causing organisms or toxic chemicals could be intentionally introduced into food or water supplies to cause mass contamination. Scientists also worry that climate change may increase the risk of contamination of crops and seafood from biotoxins, pathogenic microbes, pesticides, and other chemicals.


Of the more than 250 identified foodborne diseases, most are caused by pathogenic microorganisms. For example, the United States Food and Drug Administration (FDA) estimates that 90% of purchased raw poultry carries some disease-causing bacteria. Most pathogenic food contaminants originate from animal or human feces, and food contamination is directly responsible for many infectious digestive diseases.

In the United States, most food contamination is caused by one of eight pathogens:

Other pathogenic food contaminants are serious problems worldwide:

Seafood contamination

Seafood can be contaminated in various ways, including via agricultural and other runoff, sewage, natural toxins, mercury, and chemical pollutants in water and the food chain. Filter-feeding shellfish, such as oysters, clams, scallops, and mussels, can accumulate toxins. Scombroid is caused by chemicals produced by bacteria in fish that are not refrigerated or frozen immediately.

Toxins associated with algal blooms called red and brown tides can accumulate in fish and shellfish:

Causes and symptoms


Food can be contaminated at any point in the production chain—in the field, through animal feed, in the slaughterhouse or processing plant, during transport, in markets and restaurants, or in the home kitchen. Sources include:

Although any food can be contaminated, raw or undercooked meat, poultry, eggs, fish, and raw (unpasteurized) milk are the most common. Processed foods that pool ingredients from multiple sources are particularly prone to contamination. Washing raw fruits and vegetables reduces but does not eliminate contaminants. Improperly canned foods, luncheon and deli meats, soft cheeses, and any products containing raw eggs are subject to contamination. A few bacteria in alfalfa or bean seeds can multiply to contaminate an entire batch of sprouts. Refrigeration or freezing generally prevents bacteria from multiplying. However, L. monocytogenes and Y. enterocolitica can grow and multiply at refrigerator temperatures. High levels of salt, sugar, or acid prevent bacteria from growing in preserved foods and thorough cooking kills pathogenic microorganisms.


Although symptoms of food contamination depend on the type of contamination, abdominal pain and cramps, diarrhea, nausea, and vomiting are most common. After ingesting contaminated food, there is usually a delay before symptoms develop. However, symptoms of chemical food poisoning often appear very quickly, usually beginning with a tingling in the mouth, then in the arms and legs, followed by dizziness and possibly difficulty breathing. Symptoms of poisoning from manmade toxic chemicals that have accidentally contaminated food may develop rapidly or slowly and vary with the type of chemical and degree of exposure.


A life-threatening paralytic illness from food contaminated with botulinum toxin from the bacterium Clostridium botulinum.
A genus of bacteria that is found in almost all raw poultry.
Clostridium perfringens—
A bacterium that is a common food contaminant.
The abnormal depletion of body fluids, as from vomiting and diarrhea.
Ions such as sodium, potassium, calcium, magnesium, chloride, phosphate, bicarbonate, and sulfate that are dissolved in bodily fluids such as blood and regulate or affect most metabolic processes.
Inflammation of the lining of the stomach and intestines.
Hemolytic uremic syndrome (HUS)—
Kidney failure, usually in infants and young children, that can be caused by food contaminated with bacteria such as STEC or Shigella.
Illness caused by food contaminated with the bacterium Listeria monocytogenes.
Norwalk virus; a large family of RNA viruses that are the most common cause of illness from contaminated food.
An organism that survives by living with, on, or in another organism, usually to the detriment of the host.
A causative agent of disease, such as a bacteria, virus, or parasite.
Severe diarrhea caused by food contaminated with bacteria of the genus Salmonella.
Shiga toxin producing E. coli (STEC)—
Strains of the common, normally harmless, intestinal bacterium Escherichia coli that can contaminate food with Shiga toxin; E. coli O157:H7 is the most commonly identified STEC in North America.
Staphylococcus aureus—
Staph; a bacteria that can contaminate food.
Toxoplasma gondii—
A very common parasite that is a leading cause of death from food contamination; although it infects large numbers of people, T. gondii is usually dangerous only in immunocompromised patients and newly infected pregnant women.

Botulism, shellfish poisoning, and chemical poisoning are medical emergencies. Botulism requires hospitalization, often in an intensive care unit. Adults are given botulism antitoxin if it can be administered within 72 hours of the appearance of symptoms. Patients may require mechanical ventilation to assist breathing, as well as intravenous feeding until the paralysis passes.


Most illnesses resulting from food contamination resolve quickly without complications. However, contaminated food can cause serious and potentially life-threatening complications, especially for the very young, the elderly, pregnant women and their unborn babies, and anyone with a weakened immune system. It is estimated that 2%–3% of acute illnesses from food contamination lead to secondary long-term illnesses and complications that may affect any part of the body, such as the joints, nervous system, kidneys, or heart. Listeriosis can be serious or even fatal in newborns, the elderly, and the immunocompromised and can cause miscarriage, stillbirth, or premature birth if contracted during pregnancy. Campylobacter infection can cause Guillain-Barrésyndrome. STEC can cause hemolytic uremic syndrome (HUS), the most common cause of acute kidney failure in children. In the elderly, food contamination can even cause gastroenteritis-induced death.

Chemical food contamination is more likely to cause serious long-term health problems than the various forms of microbial contamination. Toxins in fish can cause permanent liver damage. Pesticides and other chemical contaminants can cause liver damage, kidney failure, and nervous system complications.



Most food contamination is preventable, since the CDC estimates that about 97% of all poisonings from contaminated food result from improper food handling, such as undercooking or poor refrigeration. Simple precautions in restaurants, cafeterias, and home kitchens include:

As a general safety rule, “when in doubt, throw it out.”

Parental concerns

Breastfeeding is the best way to protect infants from food contamination. Baby formula should never be left at room temperature and baby bottles must be kept clean and disinfected.

Infants and young children are particularly susceptible to dehydration from food contamination-induced diarrhea and vomiting, since they can lose water and electrolytes very quickly. Small sips of oral rehydration solution should be given to children as soon as vomiting or diarrhea begins. A physician should be consulted before giving antidiarrheal medicines to children.

See also Bioterrorism ; Biotoxins ; Chemical poisoning ; Food and Drug Administration ; Food poisoning ; Listeriosis .



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Center for Food Safety and Applied Nutrition (CFSAN), U.S. Food and Drug Administration, 5100 Paint Branch Pkwy., College Park, MD, 20740, (888) SAFEFOOD (723-3366),, .

National Agriculture Compliance Assistance Center, U.S. Environmental Protection Agency, 901 North 5th St., Kansas City, KS, 66101, (888) 663-2155, Fax: (913) 5517270,, .

Partnership for Food Safety Education, 2345 Crystal Dr., Ste. 800, Arlington, VA, 22202, (202) 220-0651, Fax: (202) 220-0873,, .

United States Centers for Disease Control and Prevention, 1600 Clifton Rd., Atlanta, GA, 30333, (800) CDC-INFO (232-4636),, .

United States Department of Agriculture (USDA), 1400 Independence Ave. SW, Washington, DC, 20250, (202) 720-2791, .

United States Food and Drug Administration (FDA), 10903 New Hampshire Ave., Silver Spring, MD, 20993-0002, (888) INFO-FDA (463-6332), .

Monique Laberge, PhD
Margaret Alic, PhD
Revised by Tish Davidson, AM

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