Board Thread:Skyrim/@comment-11204276-20130822224324/@comment-6881629-20130823103403

Magic elemental and poison resistance are capped at 85% seeing as disease is handled in the game a bit like magic i would say disease resistance is the same, resist disease 100% is actually around 85%.

There are several other threads about Werewolves catching a disease around and a UESP disscusion here if you want to look.