| Since poison ivy is not suspose to be contagious. At least that is my experience. I would say that something with the oil on it is being shared. A wash cloth or towel perhaps.
My wife told me a story which I found interesting. They were testing how much urushiol oil can be transferred. They used two subjects. The first subject wasn't allergic to urushiol oil.
The second subject was very senstive to the oil. They had the first subject touch some of the oil with his thumb. He then proceeded to touch a piece of paper 50 times. After each 50 times of pressing his thumb on the paper, he would touch the sensitive person. This continuned for up to 1000 times before the antigen lost its effect and stopped infecting the sensitive person.
Here is the link describing this. | 
