I would like to think that for Durge, since they are essentially created from the flesh of a God, they would be at least have SOME divination right? I know there is a race of children of gods but I don't think Durge is that and I am not very knowledgeable in dnd lore. But I HC that they have a little more ✨️ than the rest of the citizens of Baldurs Gate SO my silly HC is this:

Since they are mortal+ they probably never have gotten sick. Like your average cold or the flu. So in this case your resisting durge is redeemed and get downgraded to your average immune system right?

I can just imagine the first time they experience getting sick. They are not stupid. Unless that's what you want them to be. They know what a cold or flu is and how it works but experiencing it themselves is a whole different world. It's slightly terrifying not being able to keep anything down or feeling like you are being frozen alive yet your blood is boiling in your veins. I know a potion or a healing spell would burn that sickness out in a snap but I'd like to think for simple sicknesses they just have to give you a nice tea and your body has to do the rest.

I can imagine the companions and/or lover for your Durge having to comfort them and tell them this is normal and will pass. Roll the poor ex murder cult leader up burrito style and give them all the snuggles.