Food Contamination

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Food Contamination






Parental concerns



Food contamination refers to foods that are spoiled or tainted because they either contain microorganisms, such as bacteria or parasites, or toxic substances that make them unfit for consumption.


Food contamination is a serious issue because it results in foodborne diseases that each year affect an estimated seventy-six million people in the United States, while leading to some 325,000 hospitalizations and 5,000 deaths. Hence, awareness of potential sources of food contamination is an important component of good nutrition.


Food contamination can be microbial or environmental, with the former being more common. Environmental contaminants that can enter the food supply chain include pesticides, heavy metals, and other chemical agents. Many opportunities exist for food to become contaminated as it is produced and distributed. Toi start with, bacteria are present in the animals raised for food. Meat and poultry can become contaminated during slaughter through cross-contamination from intestinal fecal matter. Similarly, fresh fruits and vegetables can be contaminated if they are washed using water contaminated with animal manure or human sewage. During food processing, contamination is also possible from infected food handlers. Lastly, poor hygiene in the home is also a factor.

Bacterial food contamination

Many bacteria can contaminate food. The most common include the following:.

  • Campylobacter jejuni. Mishandling of raw poultry and consumption of undercooked poultry are the main causes of C. jejuni contamination

Cutting boards and food safety

  • Type of boards Choose either wood or a nonporous surface cutting board such as plastic, marble, glass, or pyroceramic. Nonporous surfaces are easier to clean than wood.
  • Avoid cross-contamination Use one cutting board for fresh produce and bread and a separate one for raw meat, poultry, and seafood. This will prevent bacteria on a cutting board that is used for raw meat, poultry, or seafood from contaminating a food that requires no further cooking
  • Cleaning cutting boards To keep all cutting boards clean, wash them with hot, soapy water after each use; then rinse with clear water and air dry or pat dry with clean paper towels. Nonporous acrylic, plastic, or glass boards and solid wood boards can be washed in a dishwasher (laminated boards may crack and split).Both wooden and plastic cutting boards can be sanitized with a solution of 1 tablespoon of unscented, liquid chlorine bleach per gallon of water. Flood the surface with the bleach solution and allow it to stand for several minutes. Rinse with clear water and air dry or pat dry with clean paper towels
  • Replace worn cutting boards All plastic and wooden cutting boards wear out over time. Once cutting boards become excessively worn or develop hard-to-clean grooves, they should be discarded

source: Food Safety and Inspections Service, U.S. Department of Agriculture.

(Illustration by GGS Information Services/Thomson Gale.)

  • Clostridium botulinum Bacteria producing a toxin in food responsible for botulism, the deadly paralytic nerve illness
  • Escherichia coli. A leading cause of food contamination. Based on a 1999 estimate, 73,000 cases of infection and 61 deaths occur in the United States each year. The E. coli0157:H7 strain is found in ground beef, raw milk, chicken, vegetables, and fruit.
  • Salmonella typhimurium Salmonella contamination. can occur in meats, poultry, eggs or milk products
  • Shigella The most common food that these bacteria can contaminate include: salads (potato, chicken, seafood, vegetable), raw vegetables, milk and other dairy products, and meat products especially poultry.
  • Staphylococcus aureus. Can be found in custard or cream-filled baked goods, ham, poultry, eggs, potato salad, cream sauces, sandwich fillings.
  • Vibrio cholera. These bacteria cause the well-known disease cholera that has caused many outbreaks all over the world. It can be transmitted by water or food.
  • Vibrio vulnificus. Free-living ocean bacteria that can cause food borne illnesses from contaminated seafood. Especially dangerous in the warm weather months when eating shellfish that are undercooked or raw.
  • Yersinia enterocolitica. Often found in raw milk, chocolate milk, water, pork, other raw meats.

Spoiled milk is also mostly caused by bacteria such as Lactococcus cremoris or Enterobacter aero-genes, that cause the milk to form long white strands.

Water contamination is usually due to the presence of three bacteria, E. coli, Clostridium perfringens, and enterococci, the bacteria normally found in the feces of people and many animals.

Parasitic food contamination

Parasites are organisms that lives in or on a host, and obtain nourishment without benefiting or killing the host. They enter the body through the mouth when contaminated food or drink is swallowed. There are many different types and range in size from single-celled, microscopic organisms (protozoa) to larger, multi-cellular worms (helminths) that can be seen without a microscope. Parasites that contaminate food include:.

  • Entamoeba histolytica. Parasite that causes amoebic dysentery, characterized by severe diarrhea. It is transmitted by contaminated water, and is often called “traveler’s dysentery” because of its prevalence in developing nations.
  • Giardia duodenalis. Microscopic parasite that can live in the intestines of animals and people. It is found in every region of the world and is one of the most common causes of waterborne and foodborne) illness
  • Cryptosporidium parvum. Microscopic parasite, a significant cause of water contamination worldwide. It is found in the intestines of many herd animals including cows, sheep, goats, deer, and elk.
  • Cyclospora cayetanensis. Single-celled, microscopic parasite. Little is known about this organism, although cases of infection are being reported from various countries with increasing frequency.
  • Toxoplasma gondii. Single-celled, microscopic parasite found throughout the world. Found in foods such as raw or undercooked meats, especially pork, lamb, or wild game, and in drinking untreated water.
  • Trichinella spiralis. Intestinal roundworm whose larvae may migrate from the digestive tract and form cysts in various muscles of the body. In the United States, infections are most prevalent where pork or wild game is consumed raw or undercooked.
  • Taenia saginatajsolium. Taenia saginata (beef tapeworm) and Taenia solium (pork tapeworm) are parasitic worms (helminths). They are now uncommon in the United States, although travelers and immigrants are occasionally infected.


Amoeba —A single-celled organism, many species of which live in free in water.

Amoebic dysentery —Disease characterized by severe diarrhea, caused by infection of the gut by Entamoeba histolytica

Bacteria —Microorganisms found in the environment. Bacteria can multiply quickly in food, and can cause foodborne illnesses. Not all bacteria are harmful: some are used to make yogurt and cheese.

Contamination —The undesired occurrence of harmful microorganisms or substances in food.

Cross-contamination —The transfer of harmful bacteria from one food to another, or also from hands to food.

Feces —Waste product of digestion formed in the large intestine. About 75% of its mass is water, the remainder is protein, fat, undigested roughage, dried digestive juices, dead cells, and bacteria.

Foodborne illness —Illness caused by pathogenic bacteria transmitted to humans by food.

Microorganism —A general term for bacteria, molds, fungus, or viruses, that can be seen only with a microscope.

Parasite —An organism that lives in or on a host; it obtains nourishment from the host without benefiting or killing the host. The parasites responsible for foodborne illnesses are mostly single-cell organisms such as amoeba, giardia, and trichomonas, while others have a worm-like appearance.

Pathogen —A disease-causing microorganism.


Simple precautions can reduce the risk of contamination. For instance, meat left at room temperature promotes bacterial growth and refrigeration helps to suppress it. One can also be careful about eating certain foods. Eating raw meats and fish should be avoided as well as salads prepared in restaurants where meats and vegetables share a common surface during preparation.

Most food-related illnesses can be avoided by washing fresh fruits and vegetables, cooking meat thoroughly, drinking only pasteurized milk, and common-sense hygiene. Heating food to an internal temperature above 160 °F, or 78 °C, is usually sufficient to kill parasites, viruses or bacteria, except for the Clostridium bacteria, which produce heat-resistant spores. These can only be killed at temperatures above boiling.

The Mayo Clinic offers the following advice to prevent food contamination at home:.

  • Wash hands, utensils and food surfaces often. Keeping hands, utensils and food preparation surfaces clean can prevent cross-contamination, i.e. the transfer of harmful bacteria from one surface to another
  • Keep raw foods separate from ready-to-eat foods. When shopping, preparing food or storing food, keep raw meat, poultry, fish and shellfish away from other foods. This also prevents cross-contamination
  • Cook foods to a safe temperature. You can kill harmful organisms in most foods by cooking them to temperatures between 140°F and 180°F
  • Refrigerate or freeze perishable foods. Harmful bacteria can reproduce rapidly if foods are not properly cooled. Refrigerate or freeze perishable foods within two hours of purchasing or preparing them
  • Defrost food safely. Bacteria can reproduce rapidly on meat, poultry and fish at room temperature. To defrost food safely, tightly wrap meat, poultry and fish so that the juices do not drip on other food as they thaw in the refrigerator. Another method is to put the frozen food in a plastic bag and immerse it in cold water, changing the water every 30 minutes. The sealed food package can also be placed under cold, running water. Cook food immediately after defrosting
  • Use caution when serving food. Throw out any leftovers that have been at room temperature for more than two hours or in hot weather for more than an hour. If cold food needs to sit out for longer than two hours, use a tray of ice under the food to keep it cold. If hot food must sit out for longer than two hours, use warming trays to keep the food hot
  • Throw it out when in doubt. If you are not sure if a food has been prepared, served or stored safely, throw it away
  • Know when to avoid certain foods altogether


Food contamination usually causes abdominal discomfort and pain, and diarrhea, but symptoms vary depending on the type of infection. Transmission usually occurs via the fecal/oral route with the ingestion of the pathogen present in the contaminated food. After they are ingested, there is a delay, (incubation period) before symptoms appear, that may range from hours to days, depending on the organism. During this period, the microbes pass through the stomach into the intestine, where they start to multiply. Some types stay in the intestine, others produce a toxin that is absorbed into the bloodstream, and others can directly invade the deeper body tissues. The symptoms depend on the type of infection. Numerous pathogens cause similar symptoms, for instance diarrhea, abdominal cramps, and nausea.


There are many different kinds of foodborne diseases and they may require different treatments, depending on the symptoms they cause. Illnesses that cause diarrhea or vomiting lead to dehydration if the person loses more body fluids and salts (electrolytes) than they take in. Replacing the lost fluids and electrolytes is therefore important. If diarrhea is severe, oral medication such as Ceralyte, Pedialyte or Oralyte, can be taken to replace the fluid losses. Preparations of bismuth subsalicylate, such as Pepto-Bismol, can help reduce the duration and severity of the diarrhea.


Food poisoning is especially serious and potentially life-threatening for young children, pregnant women and their fetuses, older adults, and people with weakened immune systems.

Data from the Centers for Disease Control and Prevention’s (CDC) FoodNet surveillance system suggests that although younger individuals usually face far higher rates of infection from foodborne pathogens, older adults, along with the very young are more likely to have severe complications from these infections. In particular, research has shown that the elderly are more vulnerable to gastroenteritis-induced deaths. It is also estimated that 2–3% of all acute foodborne illnesses develop secondary long-term illnesses and complications called chronic sequellae. These can occur in any part of the body, such as the joints, nervous system, kidneys, or heart.

Parental concerns

A bottle-fed infant is at higher risk for severe infections with bacteria that can grow in a bottle of warm formula if it is left at room temperature for many hours. Particular care is needed to keep baby bottles clean and disinfected. Leftover milk formula or juice should also not be kept in the bottle for many hours.



Leon, W. Is Our Food Safe: A Consumer’s Guide to Protecting Your Health and the Environment.New York, NY: Three Rivers Press (Crown Publishing Group), 2002.

Magan, N., Olsen, M. Mycotoxins in Food: Detection and Control. Boca Raton, FL: CRC Press, 2004.

Moffat, C., Whittle, K. J. Environmental Contaminants in Food. Boca Raton, FL: CRC Press, 1999.

Peariso, D. Preventing Foreign Material Contamination of Foods. Malden, MA: Blackwell Publishing Limited, 2005.

Sapers, G. M., Gorny, J. R., Yousef, A. E. Microbiology of Fruits and Vegetables. Boca Raton, FL: CRC Press, 2005.

Wilson, C. L., Droby, S. Microbial Food Contamination. Boca Raton, FL: CRC Press, 2000.


Centers for Disease Control and Prevention. 1600 Clifton Road, NE, Atlanta, GA 30333. 1-800-CDC-INFO (1-800-232-4636) or 404-639-3534.<>.

Food and Drug Administration, Center for Food Safety and Applied Nutrition. 5100 Paint Branch Parkway, College Park, MD 20740-3835. 1-888-SAFEFOOD (1-888-723-3663). <>.

U.S. Department of Agriculture, Food Safety and Inspection Service. Meat and Poultry Hotline: 1-888-MPHotline (1-888-674-6854). <>.

U.S. Environmental Protection Agency. 1200 Pennsylvania Avenue, NW, Washington, DC 20460. 202-272-0167. <>.

Monique Laberge, Ph.D.