C diff is not always acute. I'm not sure where you got the statistics that say otherwise. Many people get it, and get over it. When you get your stool culture, are you asking for it just to check for c diff? Or are you asking for an analysis of what is in you? If you are just looking for c diff, probiotics won't matter. Either the c diff toxins will be there, or they won't. Also, c diff doesn't respond well to prednisone. If you are getting positive results from pred, I'd be looking for a second opinion, and maybe treating UC/Crohn's more aggressively.
Here is a great support site for chronic c diff sufferers:
I'd particularly take a look at the threads about probiotics, and medications.
The people who post there are usually those with antibiotic resistant strains, so it might seem skewed towards people who have had infections for years. THEY ARE IN THE MINORITY! But the site contains great info, and lots of up to date research. The moderator Bobby spends a great amount of time researching and confirming information before it posted on the site.