I really wouldn't worry about it. I have eaten cole slaw many times during pregnancy, and I have never had any problems. I never knew you weren't supposed to have it, but either way, I think the chance of Listeria is VERY small. They pretty much tell pregnant women they can't have ANYTHING these days, but when we were in our mother's bellies it wasn't that way, and we are perfectly fine. I don't eat sushi, deli meat, or honey. Obviously don't drink alcohol, but other than that I try not to worry. I have been drinking a lot of Coke because it is the only thing that doesn't make me sick to my stomach, and I'm not worried about it. With all of my pregnancies I craved iced tea, and I drank it.
I'm not saying you should sabotage yourself or anything, and by all means, don't eat cole slaw if it worries you. I'm just saying, try not to worry to much about it. Everything is going to be just fine!