Cross-contamination in food

Cross-contamination is the transfer of bacteria or contaminants from one to another. In food, cross contamination occurs when the bacteria from raw foods, the utensils and surfaces used in handling them is transferred to prepared and cooked foods. This is particularly dangerous for the consumer because these prepared foods are ready to eat. So they will pass on food-poisoning organisms such as salmonella, listeria and the lethal E.coli O157 to those consuming them. Cross-contamination is a world-wide problem and takes place even in countries with highly developed food industries. In the UK, for example, specialists believe that 20% of all food-poisoning outbreaks are caused by cross contamination.

Usually, bacteria enter the kitchen with raw foods and food handlers. Illness among food handlers can play a part too. An outbreak of Novovirus which caused vomiting and diarrhoea in half of the guests at a wedding reception was traced to a cross contamination of potatoes with contaminated sink into which the food handler had previously vomited.

Bacteria can be persistent. They can live and multiply in very small cracks and crevices and in the surface cuts of chopping boards. A particularly dangerous example of cross contamination from poorly cleaned equipment was reported in the UK in 2005. A butcher, John Tudor from Bridgend in Wales, used to sell vacuum-packed cooked meats to local caterers – schools in particular – as well as vacuum-packed raw meat. Unfortunately, despite warnings from food inspectors, he used the same vacuum-packing machine for both raw and cooked meat.

Because he was careless and complacent, he spread E.coli O157 from raw meat into his vacuum-packed cooked meats. As a result, a little boy of five died and more than 100 people were confirmed as having the exact strain of E.coli since they had consumed Tudor’s cooked meats. When Tudor was sent for trial in September 2007, the court heard that the vacuum-packing machine had congealed debris and dirt on it and that his staff had been seen wiping blood off trays as they were packing cooked meats. Tudor paid a high price for his complacency. He was jailed for a year, after he admitted to placing unsafe food on the market and failing to protect food against the risk of contamination. Not all cross contamination involves bacteria.

Recently, the UK’s Food Standards Agency had to recall quiches, savoury tarts and ready meals made for food retailers Marks & Spencer and Sainsbury’s because of fears that they had become contaminated with peanuts during an incident at the factory. This could have been serious for people allergic to peanuts.

How can caterers and food businesses guard against cross contamination? A clear set of rules is essential:

– Have separate refrigerators for raw and cooked foods. If this is not possible, make sure that all foods are covered and that raw foods are stored below cooked foods. This prevents juices from raw foods dripping on to cooked or ready-to-eat foods.

– Have separate cutting boards, knives and other equipment for preparing raw and cooked foods and make sure that these are stored separately. Always clean equipment thoroughly, using detergents and sanitizers, after preparing foods, particularly raw food. Clean all food preparation surfaces thoroughly, before and after using them for food preparation. Clear up any spillages and food debris immediately and clean again afterwards.

– Never defrost raw meat or poultry in a sink. If the poultry is carrying salmonella, the sink will soon get contaminated. If poultry has to be washed, disinfect the sink immediately afterwards.

Wash hands regularly and thoroughly, especially after handling raw foods and always after visiting the lavatory. Dry thoroughly using a hot air hand dryer or throwaway paper towels. Keep clothing clean and change soiled aprons and coats immediately. Do not allow food handlers to work when they are ill but make sure that they get reasonably paid for sick leave. Otherwise, they may be tempted to conceal illness from an employer.