Food Contamination and Foodborne Illness Prevention

Food becomes contaminated through a variety of mechanisms. Some things that can contribute to foodborne illness are:

• inadequate hand washing
• cross-contamination
• storage and cooking temperatures
• contamination of food by animal waste

Hand Washing

• Pathogens can be introduced into food from infected humans who handle the food without thoroughly washing their hands.
• These pathogens are thus transferred from trace amounts of fecal matter present on hands to the food.
• Hand Hygiene: Wash Your Hands! Hand washing and Hand Hygiene information

Cross-Contamination

• Food and kitchen tools and surfaces may become contaminated from raw food products (i.e., meat and poultry).
• Microbes can be transferred from one food to another by using the same knife, cutting board or other utensil without washing the surface or utensil in between uses.
• A food that is fully cooked can become re-contaminated if it touches other raw foods or drippings from raw foods that contain pathogens.
• Prevent Cross-Contamination
  Cross-contamination is the physical movement or transfer of harmful bacteria from one person, object or place to another.

Storage and Cooking Temperatures

• Many pathogens need to multiply to a larger number before enough are present in food to cause disease.
• In general, refrigeration or freezing prevents virtually all bacteria from growing.
• If food is heated sufficiently, parasites, viruses and most bacteria are killed.
• How Temperatures Affect Food Food Safety and Inspection Service United States Department of Agriculture. Attention: Non-MDH link

Contamination of Food by Animal Waste

Many foodborne microbes are present in healthy animals raised for food.

• Meat and poultry may become contaminated during slaughter by small amounts of intestinal contents.
• Fresh fruits and vegetables can be contaminated if they are washed with water that is contaminated by animal manure or human sewage.

Toxicity in Food -

Environmental contamination of food

Substances that are either real or potential risks to health may enter the food supply as a result of contamination of the environment  But, in terms of the number of people affected, environmental contamination is less of a problem than illness caused by food poisoning from harmful microorganisms in food (see 'How to Avoid Food Poisoning').

For many environmental contaminants, health authorities recommend maximum acceptable levels that are considered to be safe in food. It is illegal for foods containing higher levels to be sold although the occasional consumption of slightly higher amounts is unlikely to be harmful. Foods are monitored to check that they comply with the recommendations. Foods that contain more than the permitted amounts of the contaminants being monitored are withdrawn from sale. The effectiveness of this depends on the extent of monitoring.

In general, the level of environmental contaminants in our food complies with the limits recommended by health authorities. However, because of the uncertainty in establishing exactly what is a safe level for many of these contaminants, it is in the interests of our general health to consume as wide a variety of foods as possible. By doing this, the chances of eating large amounts of a contaminated food are minimized. Continued and extensive surveillance and control are needed.

'Heavy metals'

The common environmental contaminants of greatest concern in food are the so-called 'heavy metals', most notably cadmium, lead and mercury.

Mercury

Almost all of the mercury in food occurs in seafood. A dramatic instance of mercury poisoning occurred in the Minimata Bay area in Japan. Fish and shellfish that were heavily contaminated by industrial waste caused poisoning in many of the people who ate them, resulting in damage to the central nervous system and in some instances death. Surveys of the levels of mercury and other heavy metals in food are regularly carried out and have shown that generally the levels are below the maximum amounts permitted by health authorities. Occasionally, higher levels are detected and the food withdrawn from sale.

Lead

Lead occurs widely in the environment and it can enter our bodies through drinking water and the air we breathe, as well as through food. Children are the group at greatest risk, because even at levels below those that produce the usual signs of poisoning, lead can cause behavioural abnormalities. The levels of lead that cause these effects are uncertain so it is difficult to estimate what amount is 'safe'. In some areas, particularly where there is heavy lead pollution in the air from leaded petrol, lead levels may be hazardous for children. Legislation to limit the total environmental lead burden is being enacted in many countries.

Cadmium

Cadmium is present at very low levels in a wide variety of foods. Poisoning due to cadmium in food is rare. The upper 'acceptable' limit for cadmium in food recommended by the World Health Organisation is generally complied with. The kidneys of animals are generally higher in cadmium than are other foods. Contamination of rice, soya bean and seafood with cadmium from local industrial and mining operations has caused cadmium poisoning.

Pesticides and industrial chemicals

Two very persistent environmental contaminants are the pesticide DDT and PCBs (polychlorinated biphenyls), which have been used in electrical transformers, plastics and paints. DDT and PCBs are not easily degraded in the environment and can concentrate in the fatty tissues of many organisms as they move up the food chain. Recent surveys in Australia have not detected the presence of PCBs in food. DDT has been found in many foods but the amounts are such that the total daily intake of DDT is within the acceptable' upper limit recommended by the World Health Organisation.

HOW TO AVOID FOOD POISONING

PERSONAL HYGIENE

1. Wash your hands before preparing food.
2. Do not smoke or comb hair when preparing food.
3. Cover any cut or pimple with dressings.
4. Do not handle pets when preparing food.
5. When tasting food do not return licked utensils to the food.

PRECAUTIONS WHEN PREPARING FOODS

1. Keep all cooking utensils and surfaces clean. Discard cracked and chipped utensils and crockery.
2. Do not use the same knives, chopping boards etc, for both raw and cooked food without first washing them.
3. Keep food as cold as possible.
4. Do not store raw food where it can contaminate cooked food. Water or blood from raw meat or fish can cause contamination by dripping onto cooked food stored below.
5. Heat food as rapidly and cook as thoroughly as possible. Remember the inside temperature can be much lower than that on the surface.
6. If the food is not to be eaten immediately after cooking, cool it as quickly as possible and keep it in the refrigerator until it is ready to be served or reheated. Large pieces of food should be sliced into smaller pieces to allow it to cool more rapidly.
7. Do not keep food warm; keep it either hot or cold.
8. When reheating food, heat quickly and thoroughly, so that even the middle of the food pieces have reached a high temperature.
9. Handle cooked food as little as possible; use serving tongs etc.
10. Discard any food that has gone 'off' (off-odour, mouldy, slimy). Storing at lower temperatures will not stop further deterioration.