It is the transfer of Bacteria or contaminants from a raw food like vegetables into cooked food.
When we talk cross- contamination in food.
We generally mean the transfer of bacteria from raw foods, and the utensils and surfaces used in handling them, to prepared and cooked food.

This is a dangerous for the human being because these prepared cooked foods are ready to eat. As they will not undergo for further washing or cooking, and this way they will pass on food poisoning organisms such as salmonella, listeria, and the lethal E. coli.
Cross-contamination is a world wide problem. Even in countries with highly developed food industries, they also are facing the problem from cross- contamination.

How Cross-contamination of food: -

Usually Bacteria come into the kitchen via raw foods such as meat, poultry, vegetables and even fruits. The food handlers can also brings bacteria on their clothing cause illness among food handlers or seller. An outbreak of NOVOVIRUS, which causes vomiting and diarrhea, affecting most of the guests at a wedding reception has been traced to cross – contamination.
These happen from potatoes as the potatoes are kept in sink where some body previously vomited. The Bacteria can be persistent and they can live in very small cracks and crevices of chopping board and the knives and in the surface cuts of chopping board.

How can caterers, food business men and the house maker protect from cross- contamination?
I have some guidelines by which we try to protect our self

1. Have separate refrigerators for raw and cooked food. 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.
2. Have separates cutting boards, knives and other equipments for preparing raw and cooked foods and make sure that these are stored separately. Always clean equipments thoroughly, using detergents and sanitary after preparing food. Specially chopping board must be washed in hot water.
3. - Wooden chopping board and wooden handle knife must be avoided as they absorb moisture which helps Bacteria to live. Use always fiber chopping board and knife of fiber handle.
4. Clean food preparation surfaces area thoroughly, before and after using them for food preparation. Cleanup any spillages and food debris immediately.
5. Never defrost raw meat and poultry in a sink. If the poultry carrying salmonella, the sink will soon become contaminated from Bacteria.
6. Wash hand after and before the handling raw food regularly.
7. keep separate clothing and clean them.
8. duster of kitchen must be wash in detergent regularly.