Intermedia aren't more prone to HITH than any other cichla. This is a common misnomer as the batch that made these fish famous back in the day were kept in subpar conditions and just about all of them came down with it in the importer's tanks.
I don't believe r1ridah bought his intermedia with hith but it later developed hith. It was also the only fish in his tank to get hith. I believe his intermedia came from the amazon don who had a really nice setup from what I remember.
I personally never experienced hith with any of my fish but I keep my water parameters in check, feed my fish quality foods, and I don't run carbon which might all have something to do with it.