Cross contamination is the physical movement or transfer of harmful bacteria from one person, object or place to another. It is a key factor in food poisoning.

Sources of cross contamination

There four common sources of cross contamination:

Food

Raw perishable foods can contain harmful bacteria. For example, raw meats contain a large number of naturally occurring bacteria such as Salmonella, Campylobacter and Listeria which are all causes of food-borne illness. Data Sheets on these and many more are available on the New Zealand Food Safety Authority website.

If you are not careful, harmful bacteria can easily be transferred from raw to cooked or ready-to-eat foods:

  • Due to incorrect storage methods - raw meat may drip blood and juices onto cooked foods such as ham, and quiche, or other ready to eat foods like salads, dressings and sauces
  • When raw and cooked foods are combined to make salad rolls, sandwiches and mixed salads - harmful bacteria may be transferred from salad vegetables to other foods (like meats, cheese or egg). If these products are then not kept refrigerated the bacteria can multiply and may cause food-borne illness.

People

Harmful bacteria live in and on our bodies, especially on and around our faces and hands, and on our clothing. As they are usually present in small numbers they do not make us sick. If these bacteria are transferred from our bodies or clothes onto food, and allowed to multiply, the food can become unsafe to eat.

Equipment

Bacteria are able to live and multiply in any cracks and crevices in equipment including the surface cuts of chopping boards. After equipment has been used, bits of food containing bacteria remain. If the equipment is not properly cleaned, when it is used next the bacteria will be transferred to another food.

Working surfaces

Surfaces such as bench tops may have bacteria on them from contact with people, raw foods, dirty equipment or other things such as cartons that have been stored on the floor. If the bench tops are not properly cleaned, any food placed on them will be contaminated by the bacteria.


Preventing cross contamination

These steps will help prevent cross contamination:

  • Make sure all staff handling food understand the how easily cross contamination can occur
  • Design the work flow and methods used in food preparation to minimise the chances of cross contamination
  • Physically separate raw foods, especially raw animal products, from all cooked, pre-cooked and pre-prepared foods during storage, preparation and display
  • Keep the handling of cooked and ready-to-eat foods to a minimum
  • Take care to prevent recontamination of cooked and ready-to-eat food contact surfaces:
    • by thoroughly washing hands after handling raw foods, especially raw meats
    • by using separate cutting boards and food contact surfaces for raw and cooked/ pre-cooked/pre-prepared foods
    • by not placing bulk food containers on bench surfaces
    • by using correct sanitation procedures for all utensils and equipment
    • by ensuring that cleaning cloths are single service or are adequately sanitised.