Cross Contamination

Contamination is the presence of unwanted material, usually micro-organisms, in food which may make it unsafe or unpleasant to eat.

The term 'cross-contamination' is used to describe the transfer of pathogens from a contaminated food (usually raw items such as meat, poultry and vegetables) to other foods, whether it occurs directly or indirectly.

The first step which will contribute to the prevention of food-poisoning is to avoid food contamination by pathogens. In simple terms this involves keeping the SOURCES of pathogens away from both food itself and any surfaces or utensils which may be used for food.

The sources of pathogens are people, raw foods, pests, pets, air, dust, dirt and food waste. Most of these may easily come into contact with food and, indeed, both people and raw foods will be found in the kitchen. Great care must therefore be taken to stop any pathogens being transferred to foods.

It is relatively simple to recognise opportunities for direct contamination where sources actually touch food. This would occur, for example, when people touch sandwiches with dirty hands, when raw meat is placed on top of cooked ham, when a fly lands on some food on the work surface or when a cat helps itself to some food from its owner's plate.

It is less obvious, but just as important, to consider the occasions when indirect contamination can occur. In other words, when the sources transfer pathogens on to something which may later come into contact with food (sometimes referred to as a 'vehicle'). This would, include, for example, when people touch a plate with dirty hands which will then be used for sandwiches, when raw meat juices are left on a knife which will later be used for slicing ham, when a fly lands on a work surface on which food is to be prepared and when a cat licks a plate on which a meal is to be served.

Personal Hygiene

People are a significant source of pathogens and may easily contaminate foods either directly or indirectly. Many people carry some type of food-poisoning bacteria at one time or another, either in their gut or on their body without necessarily knowing that the pathogens are there. It is therefore very important to take care with personal hygiene, and particularly to keep hands clean and avoid habits which could cause contamination when preparing food.

Hands and Nails

Hands are the most likely way in which a person will contaminate food because they touch equipment, utensils and, probably the food itself when it is prepared and eaten. In the course of the day, hands will also touch many sources of pathogens such as raw foods, parts of the body, rubbish, domestic pets, etc. It is therefore essential that hands are regularly and thoroughly washed using hot water and soap and then dried with a clean towel, particularly before food is handled.

Nails can also harbour dirt and bacteria. They should be kept clean. People working in the food industry have to keep their nails short and clean and cannot wear nail varnish because it can chip off and contaminate food. They should also not wear jewellery, particularly rings and watches, because these can carry bacteria and often prevent hands from being thoroughly clean even when washed.

Skin, Cuts and Spots

Many people carry bacteria on their skin, including Staphylococcus aureus which is also often found in high numbers in cuts, spots, boils and other skin sores. Cuts and sores should therefore be covered by waterproof dressings before food is handled to stop the chance of bacteria being passed on to food.

Nose, Mouth and Ears

Almost half the population carry Staphylococcus aureus pathogens in their nose, mouth and ears. It is important to avoid habits which could transfer these bacteria into food, such as coughing or sneezing over food, picking or scratching the nose or ears whilst handling food, or tasting food with a finger or even a spoon and dipping it back into the food for a second try! People in the food industry are forbidden to smoke when handling food because of the risk of their hands picking up pathogens from the mouth whilst smoking.

Hair

Hair and the scalp carry bacteria, including Staphylococcus aureus. Loose hairs and dandruff can easily fall into food and cause contamination. Hair should not be brushed or combed where it may fall into food.

Clothing

Clothes can easily pick up dirt and bacteria during the course of the day. A range of pathogens could be picked up on clothing, for example, when playing sport outside, handling pets, gardening, etc. Some clothing materials such as wool, nylon, and cotton also shed fibres which can end up in food. It is therefore important to make sure that clothes are not dirty when preparing food and it is advisable to wear an apron which will help prevent clothes from contaminating food.

Guts

When people suffer from food poisoning, they are likely to have high numbers of pathogens in their gut which will be passed out of the body in stools (faeces). The bacteria can be transferred to the hands through toilet paper because it is porous; lavatory seats, flush handles, etc. can also be easily contaminated. It is therefore very important to wash hands thoroughly after using the lavatory and it is advisable not to prepare food for anyone else if suffering from sickness and diarrhoea.

Some people carry pathogens such as Salmonella in their gut for a long time after they have recovered from their symptoms and a few people can carry Salmonella bacteria without having been ill at all. Everyone should therefore always take care with hand washing.

Summary of Practical Steps to Protect Foods from Contamination

It is important to recognise the many different ways in which contamination of foods may occur, but the following brief list summarises 'hygiene rules' which will limit contamination in the kitchen.

  • Pay attention to personal hygiene, especially hand washing.
  • Make sure crockery, cutlery, utensils, etc. are clean before they are used and are washed thoroughly afterwards.
  • Keep raw food and cooked ready-to-eat food separate at all stages - when shopping, storing and preparing foods at home.
  • Keep foods covered or wrapped.
  • Keep domestic pets and pests out of the kitchen.
  • Clean up spillages and remove food waste promptly.
  • Store rubbish in a suitable bin and empty it frequently.
  • Keep kitchen cloths clean and regularly changed, bleached or disinfected