An indirect transmission, which is known as cross-contamination, happens when microorganisms, bacteria, pathogens, allergens, fungi, mold, protozoa, yeast, foreign objects, or other harmful substances are transferred from a food, a cutting board, a work bench, a knife or other utensils, onto another food or surface. Cross-contamination can also contaminate foods or objects with allergens that can cause a customer to have an allergic reaction.
Cross-contamination is most likely to occur when a safe food is contaminated by an unsafe food for example, meat drippings contaminating food stored below it. It is also possible for a food handler to contaminate food from bacteria or other harmful substances present on the hands. Another common source of cross-contamination is safe food being used on equipment that has been contaminated, such as a slicer that was not properly washed or sanitized, or a cutting board that was used for processing raw meat that was not properly washed or sanitized. Contaminated water is also one of the most common ways for cross-contamination to occur, especially if it is used to wash surfaces within a food-service operation, or washing produce/other foods.
The most dangerous cross-contamination occurs when microorganisms are transferred from raw foods; specifically, meat products; to ready-eat foods, such as produce or breads. With the naked eye, it is often impossible to tell when a food has been a victim of cross-contamination.
Direct transmission, however, is the process of microorganisms traveling from the main source to a food. For example, touching, coughing, sneezing on food.
To prevent cross-contaminations, food handlers should always practice good personal hygiene, keep hot foods hot and cold foods cold, store foods properly, and be aware of the potential situations where cross-contamination could occur in the food service environment.