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.
There four common sources of cross contamination:
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. (external link)
If you are not careful, harmful bacteria can easily be transferred from raw to cooked or ready-to-eat foods:
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.
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.
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.
These steps will help prevent cross contamination: