Examples of cross-contamination

Example 1: Cross-contamination via utensils and tools

If the same cutting board is simultaneously used to handle raw fish and for chopping tomatoes, the latter may be contaminated with microbes from the raw fish. This cross-contamination may cause the tomatoes to be harmful to health. Similarly, contamination may occur if the tomatoes are chopped using a cutting board that was previously used to handle fish and not appropriately washed between the two tasks. Harmful microbes may be transferred via tools such as cutting boards to other foods with which they come into contact. The same cutting board or other tool should not be used to handle both fish and tomatoes also due to the presence of allergens. If a tomato contaminated with fish proteins is ingested by a person allergic to fish, the consequences may be life-threatening.

Cross-contamination via utensils and tools can be avoided by using different tools for tasks, such as cutting boards for fish and vegetables, and by ensuring that the tools are washed thoroughly after each task.

Example 2: Cross-contamination via hands

When raw minced meat is moulded into balls or patties by hand, microbes in the meat transfer into the hands. Though invisible to the naked eye, microbes in the hands can be transferred to anything that is touched unless the hands are washed thoroughly immediately after handling raw minced meat. This means that the microbes can be transferred to a water faucet or door handle, for example, if these are touched before washing hands. The microbes can then be transferred to anyone who touches the handles, and from them to further places. In this way, they may contaminate other foods and cause them to become harmful to health.

To avoid the kind of cross-contamination described above, wash hands immediately after handling the minced meat. If disposable gloves are used, these should be removed without touching their outer surface with bare hands.

Example 3: Cross-contact of gluten-free foods and gluten

When baking gluten-free bread in the same space with conventional bread, it is possible that gluten-containing ingredients come into contact with gluten-free products, for example through flour dust. As a result, the products intended as gluten-free are no longer safe for persons with celiac disease. Similarly, gluten-free bread can be contaminated with gluten-containing ingredients if, for example, the same knife or cutting board is used to slice or butter the bread. Contamination may also occur if gluten-free and conventional bread are stored in the same container or close to one another.  

This type of cross-contact may be prevented by producing gluten-free and conventional products at separate times, and by cleaning premises, tools and hands thoroughly between the tasks. An example of how to separate the production is to bake gluten-free products at the start of the day, before moving on to conventional products. Gluten-free bread must be sliced using separate cutting boards and knives and served on separate serving dishes and, if needed, covered to avoid cross-contact.  

Page last updated 3/26/2019