Contamination occurs when a food is exposed to toxins or pathogens that are harmful to humans when ingested.  There are a number of ways that a food can become contaminated.  Food products go through multiple steps and exchanges in the food chain before they are consumed – production, processing, distribution, preparation and presentation – and contamination can occur at any or all of these steps in the process as a result of mishandling.


Food production refers to the growth and harvest of fruits and vegetables, and the raising or harvesting of animals, fish or shellfish intended for human consumption. Fruits and vegetables often become contaminated when they are irrigated with water contaminated with harmful pathogens. Meat food products often become contaminated when the live animal is itself infected. This applies to all animals raised for human consumption. Not only can an infection spread, for example, among a cattle herd, but an infection can also spread from mother to calf and from a hen to the eggs she lays. Even where fish are caught in the open seas, they may be contaminated with toxins they were exposed to while in the ocean environment.


Food processing refers to the manipulation of fruits, vegetables, fish, shellfish or animals intended for human consumption to produce a food product in a different form.  Various activities occur in food processing. Processing of fruits and vegetables may include washing, sorting, slicing, shredding, chilling, storing and packaging. Fruits and vegetables are vulnerable to contamination, not only from being washed with contaminated water, but also by coming into contact with contaminated equipment used to sort, slice, shred, store or package them. Food products, such as nuts, may be roasted, stored, chopped, pureed, chilled, and packaged; such products are subject to contamination at any part of the process. The processing of meat products often involves skinning, slaughtering, cutting, grinding, smoking, cooking, and freezing of the various parts of the animal raised.  If the animal’s coat is contaminated or if its intestines are infected, the contamination can spread via equipment used at any part of the process.


Food is distributed multiple times before it ends up in a kitchen cabinet. Food is transported from the farm to the production plant and, after processing and packaging, may move from the plant to one or more storage or distribution facilities to await transport to its final destination, such as a grocery store or food establishment.  Possibilities for contamination arise when food is stored in an inadequate storage or chilling facility, or is left on a loading dock in warm weather, exposing the food to thaw and allowing harmful bacteria to grow.  Produce may be exposed to contaminants when it comes into contact with surfaces of a truck or storage facility that have not been properly sanitized. If packaging gets torn or broken, the food contents may become exposed to contamination and may contaminate other foods stored or packed nearby.

Preparation & Presentation

Preparing food for ultimate consumption involves many steps, and contamination and cross-contamination can occur at any point. Contamination can occur if a food preparer handles food with unwashed hands after using the restroom, sneezing, or coughing, or where a food preparer moves from handling one contaminated food to another. Similarly, cross-contamination can occur when the same equipment, such as a cutting board, knife or other utensil, is used for different foods without proper washing and sanitation of the equipment in between uses. Cross-contamination is especially risky when meat juices are present.

Undercooking or improper freezing during the preparation process can allow harmful pathogens to remain in the food and multiply. Improper storage and improper reheating is often a cause of bacterial growth and resulting foodborne illness.  Further, when food is presented for serving and consumption and is allowed to cool or sit at room temperature too long before being consumed, the conditions may be ripe for bacterial growth.  Various pathogens can grow quickly on food kept at room temperature.