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Even greens that are sold as pre-washed should be washed to avoid contamination problems, says public health expert Dr. Karl Kabasele. (Michael Probst/Associated Press)

Food-borne bacteria and toxins are often impossible to detect on your food or in your kitchen until you get sick. Dr. Karl Kabasele, CBC's medical specialist and a public heath physician in Toronto, answers questions about how you can prevent E. coli and other bacteria from getting into your food.

How does E. coli bacteria end up on, or in, food?

E. coli bacteria  occur naturally in the intestines of animals and people, and it is plentiful in fecal matter. The processing of meat and other animal products may lead to inadvertent contamination with fecal matter, and therefore meats (and particularly ground meat) are among the highest-risk foods. Fruits and vegetables may also become contaminated on the farm if animal wastes inadvertently get into the soil or water supply where produce is grown.

E. coli can be introduced into food at any point along the chain of food production by contaminated containers, utensils and surfaces, or because of food handling by people who are ill.

Why is safe food handling so important?

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Dr. Karl Kabasele is a Toronto public health physician.

Safe food handling is important to minimize the risks of contaminating food with infectious organisms that cause food poisoning. The Canadian Food Inspection Agency estimates that 11 million to 13 million Canadians are sickened by food each year.

Who is at greatest risk?

At greatest risk of food-borne illness  are very young children, the elderly, pregnant women and people with weakened immune systems. In general, these people are more likely to suffer severe illness and complications that may require medical attention or hospitalization.

What foods should we be cautious around?

The foods that are most risky when it comes to food poisoning include meats, dairy products, eggs, seafood and prepared salads. In public health circles, high-risk foods are defined as those which support the growth of harmful germs, especially where no further steps are taken to kill or reduce the amount of germs in that food.

The highest risk foods are generally those with high protein content and a neutral pH (not excessively acidic or alkaline). As a result, meats and animal products tend to be excellent breeding grounds for micro-organisms. That includes unpasteurized dairy products and undercooked eggs. But any food can be risky if it is allowed to remain for more than two hours in the temperature "danger zone," between 4 C and 60 C, so store cold foods in the refrigerator and keep hot foods hot by consuming immediately after cooking or holding them in chafing plates for prolonged service.

Many foods, (especially fruit and vegetables) come pre-washed and packaged. Do they need to be washed? What about frozen vegetables?

As a precaution you should wash all produce with running water and friction, even if the packaging says that it is pre-washed. This is because you can't be sure how thoroughly the product was washed, and you can't guarantee that it wasn't re-contaminated after washing. Frozen vegetables should be thoroughly cooked but if you will be thawing them and consuming them raw, wash them. What precautions should people take when handling food?

The best way to minimize the contamination of food in your kitchen can be summarized in a four-part framework:

1. Clean: Wash foods thoroughly with running water and friction, keep kitchen surfaces clean by disinfecting them, use clean utensils, dish cloths and towels for each step of the food prep process, and wash your hands frequently with warm running water and soap.

2. Separate: Avoid cross-contamination by separating raw from cooked food in your grocery bag and at home, store raw meats, seafood and poultry at the bottom of the refrigerator so the juices don't drip down on other foods, and use separate plates, utensils and cutting boards for raw meats, seafood and poultry.

3. Cook: Ensure that all meats, seafood, poultry and eggs are thoroughly cooked, use a probe thermometer to ensure the food is cooked all the way through to the right temperature (consult a temperature guide for the food you're cooking). If re-heating, bring the food all the way back up to cooking temperature.

4. Chill: Keep foods cold for storage to slow the growth of harmful germs; refrigerate or freeze leftovers, perishable foods and prepared foods, don't leave risky foods out at room temperature for more than two hours, don't overcrowd your refrigerator and freezer, and allow room for cold air to circulate.

There's a debate as to whether people should use plastic or wood cutting boards. Which would you recommend and why?

I would recommend using plastic cutting boards because they can be more easily washed at high temperatures in the dishwasher and sanitized with a mild bleach solution. Softer wood cutting boards may also be prone to developing nicks and dents where germs can hide and multiply. Whichever type of cutting board you choose, be sure to wash them thoroughly, sanitize them, and use separate cutting boards for raw meat, seafood and poultry.

What if you only have one cutting board?

You can use the same cutting board to prepare different foods if you wash it thoroughly and dry it. If you were preparing raw meats, seafood or poultry you should sanitize the cutting board with a bleach solution before using it again (a half teaspoon of bleach in a litre of water).

How should cutting boards be cleaned and sterilized?

You should wash your cutting board with warm water and dish soap, taking care to remove all food scraps. Dry your cutting board and then sanitize it with a bleach solution (a half-teaspoon of bleach in a litre of water).

What about cleaning tools used in the kitchen? What practices do you recommend to prevent bacteria from spreading?

Any object or surface in the kitchen can harbour germs, but towels, dishcloths and sponges can be particularly bad because they tend to be warm and moist, the perfect conditions for multiplying bacteria. To minimize contamination, consider using disposable paper towels instead of reusing the same cloth or towel, or have multiple cloths on hand so you can change to a fresh one for each new task in the kitchen. For sponges, rinse them well when you are finished using them and let them air dry - when they get old, toss them out.

Are there any other areas of the kitchen people should be concerned about?

Any place that dirty hands touch may be carrying harmful germs so take care to regularly clean and sanitize faucets, appliance handles, counters and other surfaces. Liquid soap in a pump dispenser may be more convenient and sanitary than bar soap, but remember to clean the dispenser from time to time. If you are using a probe thermometer, clean it with a disinfecting solution between each use to avoid cross-contamination (or re-contamination of the same dish).

What advice would you give to those who are picnicking or camping?

The challenge with preparing or eating foods outside is that it can be more difficult to practise safe food-handling techniques. If you are picnicking or barbecuing, begin by doing as much of the prep at home in the kitchen, using sanitary technique. Keep raw foods away from cooked foods, and pack each food item in a resealable container. Remember to store perishable and risky foods in a cooler filled with ice, and only take them out when it's time to cook them or consume them. Similarly, if you're barbecuing, cook meats, seafood and poultry to the recommended temperatures and use a probe thermometer to ensure that they are cooked throughout.

If you are camping, try to take canned or non-perishable food items as much as possible. If you must bring perishable or risky foods, keep them in a cooler until you're ready for them, with each type of food in a resealable container to avoid cross-contamination and to keep insects out.

Reader Questions

We asked readers to send us their questions and comments to Dr. Karl. Here are his responses:

Are there any natural or less harsh alternatives to chlorine bleach that can be used to sterilize cutting boards?

Bleach is recommended by public health officials for sanitizing surfaces at home because it’s safe to handle and mix with water, readily accessible and inexpensive, and it continues to kill germs on surfaces even after you’re done cleaning. There are alternatives to bleach but each has shortcomings:

  • Alcohol – effective against bacteria, fungi, and most viruses, does not leave stains or residue but odor may be a problem and you must wash surfaces first before using alcohol as a disinfectant.
  • Hydrogen Peroxide – effective against bacteria, viruses, fungi and spores, can be used for washing and sanitizing simultaneously, environmentally friendly, and odor-free, but not good for prolonged use on soft metals like copper and brass.
  • High-temperature steam machines – can be effective against bacteria, viruses and fungus, can clean and disinfect surfaces.

Vinegar can be a good cleaning agent but it is ineffective as a disinfectant.

What is the effect of using anti-bacterial products on evolving resistant strains of E. coli?

According to the U.S. Centers for Disease Control and Prevention (CDC), "Antibacterial-containing products have not been proven to prevent the spread of infection better than products that do not contain antibacterial chemicals", so you don’t need to use commercial anti-bacterial products at home.

There is some laboratory evidence that anti-bacterial products can promote the growth of resistant bacteria, but in the real world there is no evidence that the use of anti-bacterial products leads to any human health effects. However, Health Canada has recommended that people avoid using anti-bacterial products at home as a precaution.

How does one avoid E. coli contamination when using organic/manure fertilizer in the garden?

According to a 1998 article on composted animal manures from the University of Hawaii, high quality composted manure fertilizers should be thoroughly decomposed and relatively free of harmful microorganisms. The key is that in the composting process the pile of manure and organic materials should reach a through-and-through temperature of at least 55 C (131 F) for at least five days in order to kill most germs. Having said that, there is always the possibility that there may be harmful germs in if the compost pile, especially if it has been re-contaminated with dirty tools or contact with or runoff from unsanitized piles of manure. Also, parasites and their eggs that may be present in manure may be more difficult to kill in the high temperature composting process.

Because of this uncertainty about produce grown with organic fertilizers (and any produce for that matter), it is best to assume that all produce that you bring into your kitchen is potentially contaminated with bacteria, and to use safer food handling techniques to minimize risk to your health. That includes washing all produce well under running water, peeling fruits and vegetables where appropriate, and cooking thoroughly whenever possible.