Containing microbiological cross-contamination

01 June 2001

Cross-contamination is the transfer of pathogenic (disease-causing) microbes from contaminated foods (usually raw) to other foods, either directly or indirectly. It is a major cause of food poisoning, but is easy to prevent.

Food poisoning is caused by ingesting pathogenic microbes or toxins produced by some of these organisms. Vomiting and diarrhoea occur when the organisms release toxins in the food, or when they multiply beyond certain levels in the gut. The level at which symptoms appear varies from person to person, depending on age, health status, and a number of other factors.

Pathogenic microbes can potentially be found more or less everywhere. As a consequence they may be found in raw foods that are to be cooked such as meat, poultry, eggs and vegetables. This is not usually a problem, as thorough cooking of fresh foods will render the small numbers of microbes harmless. The danger of cross-contamination arises when microbes are spread from raw to ready-to-eat foods such as cheese, salads, sandwiches, etc. or to ready-to-eat prepared dishes. An example of a way in which cross-contamination might occur in a refrigerator is by liquid dripping from raw meat or poultry on to ready-to-eat items.

There are, however, many less apparent routes that the microbes can take. Unwashed hands, dishcloths, chopping boards or any kitchen utensil that has been in contact with raw food are all high on the risk list. Fortunately, there are simple measures that can be taken to prevent cross-contamination.

First of all, always wash your hands before preparing food, and after handling raw foods. Cover any cuts with waterproof bandages and do not prepare food for others if you are sick or have a skin infection. Remember that all raw foods are potential sources of contamination and store them separately from ready-to-eat foods. For example, in the refrigerator, store raw meat and poultry below other foods and put them on a plate to prevent dripping. It makes no difference if the raw material is free-range or organic. The risk is the just the same.

Never use the same utensils for preparing raw and cooked foods. This might be easily overlooked when preparing a barbecue. Use separate utensils and plates for raw and cooked meat. Do not prepare salads on cutting boards that have been used for raw meat. It is a good idea to have a cutting board that is used only for meat. Clean all utensils thoroughly with hot water after use.

Cleanliness in general, is essential. Kitchen work surfaces should be regularly cleaned with hot water and detergent and kept free of domestic pets. Dishcloths, tea towels, hand towels and aprons should also be washed frequently at high temperature. After use, dry them quickly to prevent the multiplication of any microbes present. Floor cloths must obviously be kept separately, but maintained in the same way. Ideally, cutlery and crockery should be allowed to drain and dry naturally, or by using a dishwasher.

Lastly, cleaning agents and other items that contain antibacterial agents may be effective in limiting cross-contamination, but they are not completely effective. They should be regarded as an additional barrier and not as a foolproof safeguard.