The study, entitled "Assessment of the Potential for Cross Contamination of Food Products by Reusable Shopping Bags," was conducted by researchers from the University of Arizona and Loma Linda University. Through interviews and reusable bag tests, the researchers discovered that few consumers wash their reusable bags and a "potential significant risk of bacterial cross contamination exists from using reusable bags to carry groceries," particularly when raw meat and fruits and vegetables are carried in the same bags. Furthermore, they detected coliform bacteria in more than half of the bags and E. coli in 12 percent of the bags. Keeping the bags in the trunk of a car could increase the bacteria tenfold.
Is this something to worry about? Shots, NPR's health blog, says no and points out some shortcomings or even misleading aspects of the study. In addition to noting that the study was funded by the American Chemistry Council ("which by the way represents some disposable plastic bag makers"), NPR reports that most of the bacteria and even E. coli strains the researchers found are not harmful.
Still, it's probably not a bad idea to wash our shopping totes and produce bags from time to time. (The researchers concluded that hand or machine washing could reduce the numbers of bacteria in reusable bags by more than 99.9 percent.) For bags that can't be laundered, cleaning might be done with a cloth and warm, soapy water and/or white vinegar, followed by a thorough dry in the sun.
• Reusable Shopping Bags: Green But Unclean (Discovery News)
• Bacteria May Grow In Reusable Grocery Bags, But Don't Fret (NPR)
(Pictured: Single Large Happy Reusable Vegetable Bag in Blue from Etsy seller wonderthunder)