Today I spent a couple of hours with some new family and consumer science extension agents talking about the history of food safety, how risk is calculated and how messages should be based on data - not conjecture. We talked about why the FDA model food code provides guidance on a specific water temperature for handwashing (100F/38C). It's mainly because folks might be more likely to wash hands when water is warm (except no one can point to that in the literature), that fat is more soluble and soap lathers better. But some research has shown that temperature isn't a factor in pathogen removal at all (which is the desired outcome of the action).
One of the agents asked me how something like that gets into and stays in a regulatory document and I responded by saying "It probably seemed like a good idea to someone, and it stuck."
I feel the same way about the discussion about the safety of reusable bags.
The Academy of Nutrition and Dietetics has put out a press release saying that reusable bags need to be washed regularly by users as pathogens grow well and cross-contamination is likely.
From the release:
Reusable grocery totes are a popular, eco-friendly choice to transport groceries, but only 15 percent of Americans regularly wash their bags, creating a breeding zone for harmful bacteria, according to a survey by the Home Food Safety program, a collaboration between the Academy of Nutrition and Dietetics (formerly the American Dietetic Association) and ConAgra Foods.
“Cross-contamination occurs when juices from raw meats or germs from unclean objects come in contact with cooked or ready-to-eat foods like breads or produce,” says registered dietitian and Academy spokesperson Ruth Frechman. “Unwashed grocery bags are lingering with bacteria which can easily contaminate your foods.”
Sort of.
Williams and colleagues (2011) have published the only peer-reviewed study on the microbial safety of reusable bags and tested growth of Salmonella in 2 batches. They spiked the bags with 10^6 cfu and let them sit in the trunk of a car for 2 hours. One of the batches, where the temperature reached 47C/117F, showed a one-log increase in the Salmonella. The other batch, where the temperature reached 53C/124F, there was a one-log reduction. That data doesn't show just a breeding zone - it shows they can be a killing zone too (and I'm not sure how realistic a 10^6 contamination really is).
The part of the press releases that is the least rooted in science is that pathogen-containing bags "easily contaminate your foods." The same Williams study showed generic E. coli is floating around in bags, recoverable in 12 % (n=58) of those tested but can it be (or is it likely) to be transferred to any ready-to-eat foods, or somehow to food contact surfaces in the home?
Just because the bacteria might be there, doesn't mean it can contaminate a ready-to-eat food. No one has presented data to support that. Maybe the Academy of Nutrition and Dietetics - if so, they should share it.
In a cross-contamination event there is a dilution effect when it comes to transfer. 1000 cfus of Campylobacter on the outside of the package of raw chicken might become 100 cfus when transferred to the bag, and then only 10 cfus when transferred to ready-to-eat apples.
Washing bags frequently (as the Academy of Nutrition and Dietetics suggests) is probably a good idea (like washing hands in warm water) and probably won't increase risk, but I wonder how much it decreases the probability of cross-contamination when compared to doing nothing.
I prefer to bike to the grocery store with my kid in the trailer and dog on the leash – and put the groceries in my knapsack. With daytime highs of 100F, that ain’t happening so much at the moment.
A new report issued today by the University of Arizona and Loma Linda University in California says those reusable grocery bags can be a breeding ground for dangerous foodborne bacteria and pose a serious risk to public health.
Maybe.
Maybe it’s Gotcha microbiology where a bug is found, but the public health significance isn’t matched up with epidemiology (where are the sick people).
The American Chemistry Council, which underwrote the research project, may be a fine organization – and I’m all for industry sponsoring research – but why not release the results in a peer-reviewed journal?
Reusable grocery bags are indeed friendly to the environment but studies have shown that these bags may harbor foodborne pathogens. As such, it is important to wash your reusable bags frequently, just like you would with your dirty socks. Simply wash the bags using soap and water, machine dry, and reuse. The use of bleach may be overkill especially when the bags are meant to be environmentally friendly. It is also a good idea to separate ready to eat foods, such as produce, from meat, poultry, and fish to prevent cross contamination. Perhaps designate one bag or bin for meat and meat products and all others for ready to eat products. I have also noticed that people tend to reuse their plastic bags as well, in particular, to carry lunches. Remember that bacteria aren’t picky and if that bag had been carrying raw meat, there’s always the potential of pathogenic bacteria being present, it doesn’t take much.
Reusable grocery bags contaminated with E. coli, other bacteria***
These bags may be friendly to the environment, but not necessarily to you, according to a new report by researchers at two universities.
Reusable grocery bags can be a breeding ground for dangerous food-borne bacteria and pose a serious risk to public health, according to a joint food-safety research report issued today by the University of Arizona and Loma Linda University in California.
The research study – which randomly tested reusable grocery bags carried by shoppers in Tucson, Los Angeles and San Francisco – also found consumers were almost completely unaware of the need to regularly wash their bags.
"Our findings suggest a serious threat to public health, especially from coliform bacteria including E. coli, which were detected in half of the bags sampled," said Charles Gerba, a UA professor of soil, water and environmental science and co-author of the study. "Furthermore, consumers are alarmingly unaware of these risks and the critical need to sanitize their bags on a weekly basis."
Bacteria levels found in reusable bags were significant enough to cause a wide range of serious health problems and even death. They are a particular danger for young children, who are especially vulnerable to food-borne illnesses, Gerba said.
The study also found that awareness of potential risks was very low. A full 97 percent of those interviewed never washed or bleached their reusable bags, said Gerba, adding that thorough washing kills nearly all bacteria that accumulate in reusable bags.
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And prudence before plastic pushers.
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