Cross-contamination in food is one of the common causes of foodborne illness. Micro-organisms originated from many sources can contaminate food including safely cooked, ready-to-eat food during the food preparation and storage processes. Preventing cross-contamination can help to eliminate the incidence of foodborne illness.
It refers to the transfer of harmful bacteria from a source to food products either by direct or indirect contact.
The common routes of cross-contamination are:
Raw perishable food can contain harmful bacteria. For instance, raw meats contain a large number of naturally occurring bacteria such as Salmonella, Listeria and Campylobacter, which cause foodborne illness. Hence, harmful bacteria can be transferred from raw to cooked or ready-to-eat food.
For example:
- Meat drippings from raw meat placed on the top shelf of the refrigerator may drip onto ready-to-eat food that is placed on a lower shelf.
- Placing improperly packed raw food next to ready-to-eat or cooked food in the refrigerator.
Bacteria are able to multiply in cracks and crevices found in equipment. If kitchen equipment and utensils are improperly cleaned, the bacteria can be transferred to another food. For example:
- Use of the same knife and cutting board for cutting different types of food such as raw food, followed by ready-to-eat food (e.g. salads) without thorough washing of the knife and cutting boards.
Work surfaces such as kitchen tabletops may contain bacteria as a result of contact with dirty equipment, raw food and people. If the surface is not cleaned thoroughly, the bacteria would contaminate any food that is in contact with the surface. For example:
- Cartons that are stored on the floor would contaminate the surfaces if next placed on the tabletops.
People can be a source of cross-contamination to food. This is because harmful bacteria live in and on our bodies, especially on and around our faces, 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 to food and allow to multiply, the food can become unsafe. For example:
- Touching of raw meats and followed by slicing of cooked hams without washing hands between tasks.
- Inadequate hand washing and poor personal hygiene of food handlers.
It may cause foodborne illness when the bacteria are transferred onto food that is ready-to-eat. For instance, a customer consumes a cooked chicken that comes into contact with raw meat; the customer will consume the bacteria found on the meats that could later make him or her feel ill.
As cross-contamination can occur in many ways, the following tips can help to prevent cross-contamination and reduce hazards to our food:
- Separate raw meat, poultry and seafood from other food in the shopping cart.
- Keep raw meat/poultry or ready-to-eat food or food that can be eaten raw in different shopping bags to prevent the juices of the raw food from cross-contaminating the ready-to-eat food/food to be eaten raw.
- As raw food are potential sources of contamination, store raw food separately from ready-to-eat food.
- Place packages of raw meat, poultry or fish in a plate before refrigerating and place at the bottom shelf of the refrigerator so that the juices would not drip onto other food. Do not use the same plate that is used to hold raw meat, poultry or fish to place cooked food.
- Store fresh fruit and vegetable in clean plastic bags when not in use and away from raw meat or seafood products in the refrigerator.
- Keep food covered and elevated from the floor during storage and handling.
- Place food that is likely to spill in a suitable covered tray or container and place it in the lower part of the refrigerator.
Pay attention to personal hygiene during food preparation.
- Keep hands clean by washing hands thoroughly with soap including fingertips thoroughly before, during intervals and after food preparation, changing tasks and returning from breaks.
- It is essential that jewellery worn in hands such as rings be removed before preparation of food as they may harbour food poisoning organisms.
- Avoid touching of your face, skin and hair or wiping your hands on cleaning cloth.
- Food handlers should cover any cuts with waterproof bandages.
- Do not prepare food for others if one is sick or has a skin infection.
Use separate utensils for preparing raw food and cooked/ready-to-eat food.
- Use different serving plates for raw food and cooked/ready-to-eat food. Never use the same plate without washing it thoroughly before use.
- Ideally, use a separate cutting boards and knives for cutting raw meat/seafood products and for slicing cooked or ready-to-eat food. Alternatively, wash cutting boards thoroughly between usage of raw food and cooked or ready-to-eat food. Replace cutting boards that become excessive worn out or develop hard-to-clean grooves.
Wash and sanitise all equipment and utensils that come into contact with food with water and soap between tasks and handling raw and ready-to-eat food.
- After preparing raw food in a food processor, clean the parts of the equipment thoroughly.
- Keep all work surfaces clean between each task to remove all food scraps, crumbs spillage or spots that serve as potential reservoir of bacteria.
- Discard food that has dropped on the tabletop or on the floor.
- Regularly change, wash and sanitise cloths used for wiping tables or equipment. Never use cloths for cleaning dirty areas to clean anything that may come into contact with food.
- Do not recycle used food packaging and paper bags for storage of food.
- Always use a clean plate.
- Never place cooked food on a plate or cutting board that is previously used to hold raw meat, seafood or poultry.
- Wash fresh fruits and vegetables thoroughly to remove soil and residue prior to serving. Trim any bruised areas before eating to reduce the risk of consuming harmful bacteria which may be present naturally in the food.
- Refrigerate or freeze leftovers within two hours in clean shallow, covered containers to prevent harmful bacteria from multiplying.
- When in doubt, discard leftovers.
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