Q: What is the relapsing rate in Clostridium Difficile Colitis (CDI) ? 

Answer:  About 25% 

Clostridium difficile Colitis (CDI) remains a huge healthcare related issue. In patients with already diagnosed CDI, high vigilance is required, as relapses of CDI is up to 25%. Recently, it has been reported  that recurrence is seen in 15–35% of patients after an initial episode, with the rate rising to 35–65% after the first recurrence!

Reference: 
 Johnson S. - Recurrent Clostridium difficile infection: a review of risk factors, treatments, and outcomes. J. Infect. 58, 403–410 (2009)