Since the ban on plastic bags went into effect here in Connecticut, you need to remember to bring those reusable bags with you when you go to the grocery store. Once you've committed that to part of your muscle memory, you can't forget to clean those bags, too. Those cloth bags can serve as a breeding ground for bacteria that causes food poisoning when it comes in contact with raw foods. The same rule applies if you’re mixing food items with bleach in the same bag you’ve been using for an extended period of time.
It seems obvious enough, since cross-contamination can easily occur in kitchens, the surfaces of our reusable bags can also be contaminated by the things we place inside them. You should actually have separate bags for items like raw meat and fish, another for non-edible items, and a third for produce. That way you can ensure that you're not accidentally contaminating the fresh foods you just purchased. And don't forget to wash those reusable bags, too. You should clean them the same way you would clothing, to get rid any unwanted bacteria.
It may seem like a lot of extra work, but that E coli and campylobacter, two deadly bacteria that can cause stomach bugs and other illnesses, has been proven to transfer from packaging to the interior of reusable bags even when it hasn't been torn or leaked open.