Oh man that sucks! My heart goes out to you......
But in answer to your reply, I have always had some form of allergy (skin rash) to weeds, chemicals, sun, soap, and plants.
However, I have never ever had a skin rash due to a jacuzzi, but the last 2 times (2 months apart) I used the jacuzzi at my condo in Palm Springs, I broke out in a rash. Once on my lower back and once on my R upper thigh.
The first time my doctor issued some kind of antibiotic and I think it was called hot tub or pseudomonas folliculitis, which is a bacterial infection. The second time, it just cleared up in about 2 weeks.
Nobody else got this rash and I have never had it at our condo jacuzzi before. Therefore, yes, I believe that MS causes you to be more susceptible to anything and everything contagious. This is also why they strongly recommend you and all family members get a flu shot.
If you have had poison ivy before, you may find that it will take a little longer to clear up this time.
Now remember, no scratching or you will just spread the rash more!
Take care, Les