At the camp I was at there was a patch of poison ivy behind the pools. I walked through it a few times before I realized it was there. They had mowed it down, so it didn't look like a normal patch of poison ivy since you had to look at the small plants that hadn't been cut down. Once I realized I had been walking in the stuff I washed off my feet right away. I didn't get any, but I tend not to catch poison ivy easy.
I would say the best way to avoid poison ivy is to know what it looks like. Just like you avoid glass and other obstacles, poison ivy should be avoided even if you are shod. It tends to grow along the edge of the woods and near stone walls and has leaves of three, so let it be. Other plants also have three leaves, but it is better to be safe than sorry. I've never seen poison ivy and mushrooms growing in the same location. I believe poison ivy likes a location with more sun than your typical mushrooms.
Knowing how one gets poison ivy can also help you avoid getting it. Poison ivy has a sticky oily resin (urushiol) that can last years on your shoes and clothing. It can be easily removed with soap and water, though they do make special soap that is suppose to work better. Treat all clothing that may have come in contact with the oil like you would a contaminated item. You don't want to spread the oil on other items in the house.
From what I understand the oil needs to penetrate your skin before the reaction occurs, so the sooner you wash it off the better you are. Pets can also run through the stuff and then pass the oil on to you. Thick tough soles may help slow any adverse reaction down, though I'm sure there has not been any studies done to prove this. Hmm, maybe we could conduct a study. Anyone interested in helping? You just need to rub some poison ivy on your soles, and a few other random places on your body and report the results. I wouldn't qualify, since I tend not to get a reaction, otherwise I would be glad to do the study myself.
There are some creams that you can apply before hand, though I have no experience with them. I had a friend tell me he took a series of pills when he was younger that stopped him from having a reaction to poison ivy.
Good luck hunting mushrooms.
