Cross Contamination

Cross contamination is the transfer of bacteria or viruses from a contamination source to a food. This can occur directly or indirectly. Direct transfer would be by contact with the food such as in a refrigerator by incorrect storage of raw and ready-to-eat foods. Indirect contact would be by a 'vehicle' which transfers bacteria or viruses from one surface to another and then onto the food. The presence of E. coli in food can indicate fecal contamination and poor hygiene.

E.coli is found in the intestinal tracts of humans and animals such as cattle, in sewage, animal carcasses and in water. There are 6 pathogenic groups of E.coli with E.coli 0157:H7 causing severe illness and only requiring a small infective dose of 10 cells or less.

To avoid cross contamination of E.coli, work areas, surfaces and equipment used for raw and ready-to-eat food should be adequately separated. All food businesses should consider any potential sources of E.coli from raw meats particularly ground beef and poultry, unwashed fruits and vegetables from soil, raw milk and raw milk products, and frozen produce which is not ready-to-eat. These potential sources  of E.coli can then be spread to other areas indirectly by surfaces, hands, equipment used for handling raw food e.g. chopping boards and knives, cleaning cloths and by dual use of complex equipment such as vacuum packers, slicers and mincers (used for preparing both raw and ready-to-eat foods).

If equipment and utensils such as chopping boards and knives are used for raw and ready-to-eat

food, they should be disinfected by heat (e.g. a sterilising sink or a steam cleaner), or by using a full dishwasher cycle between uses. The rinse cycle of commercial dishwashers should reach 82°C and should be tested daily to ensure this is reached. However, best practice is to use separate colour coded equipment and utensils for handling raw and ready-to-eat food.

The common colour coding system is red for raw meat, green for salads & fruits, blue for raw fish, yellow for high risk ready-to-eat cooked meat, brown for vegetables and white for bakery and dairy. Some colour coding systems also use purple for allergens.

Separation is key to preventing cross contamination of E.coli. Best practice is separation by rooms and staff, as well as by separate utensils and equipment.

There is a risk of cross contamination where staff cross over from serving and handling of raw foods to ready-to-eat foods. I have previously spotted on one inspection where raw meat was sold in a butchery with an adjoining fishmongers. There was a risk of indirect contamination of E.coli from raw meat to ready-to-eat fish and shellfish in the adjacent fishmongers caused by staff shortages. Staff serving on the butchery would then serve on the fishmongers and handle ready-to-eat fish without hand washing or changing clothing once it was contaminated. In this case hand washing is key to preventing cross contamination and using safer working practices such as ideally having separate staff for handling raw and ready-to-eat food. Hand contact can also be minimised with use of tongs and these can also be colour coded. Clothing does not have to be changed but there is a risk if it becomes contaminated and best practice is to have different sets of clothing for staff handling raw and ready-to-eat food and ideally different staff.

If complete separation by room is not possible, separation by area can be used as an alternative - although this is not the best way to prevent cross contamination. This could be a permanent specific area or worktop in the kitchen with separate equipment and utensils. Temporary separation arrangements by space or time separation should be used as a last resort. This should be used in conjunction with.strict cleaning and disinfection between processes of the work preparation area, equipment and utensils. However, this carries a risk and complete separation is best practice.

Dual use of complex equipment should only be done where equipment is fully dismantled and disinfected between uses. The manufacturer's instructions to dismantle equipment need to be followed to ensure all hard to reach areas are cleaned. Vacuum packers should only be dismantled by a competent engineer. For slicers and mincers dismantling equipment is easier but this cannot be done effectively in a typical busy working day and should be done when a business is not operating. It is good practice to colour code or label complex equipment to ensure staff know its intended use to prevent cross contamination.

Preventing cross-contamination is a key factor in preventing food-bourne illness.