Recurrent C. difficile infection (rCDI) occurs in 20-25% of patients after the first episode and 40-65% after a second episode, driven by failure to restore the protective colonic microbiome. The disrupted gut flora cannot provide colonization resistance, allowing persistent C. difficile spores (which survive standard treatment) to germinate and re-establish toxin-producing infection. Fidaxomicin is a narrow-spectrum macrocyclic antibiotic that inhibits bacterial RNA polymerase, selectively killing C. difficile while preserving the anaerobic gut flora essential for colonization resistance — this microbiome-sparing property reduces recurrence rates by approximately 50% compared to vancomycin. For patients with multiple recurrences, fecal microbiota transplant (FMT) directly restores the diverse colonic microbiome, achieving 80-90% cure rates by re-establishing competitive exclusion of C. difficile.