Severe CDI was associated with a higher APACHE II score (p < 0.001), onset of CDI in the intensive care unit setting (p = 0.019), higher C-reactive protein level (p < 0.001) and concurrent antibiotic use for treating infections other than CDI (p = 0.003) compared with mild-to-moderate CDI but only high C-reactive protein was an independent risk factor of severe CDI (aOR 1.015; 95% CI 1.008–1.022; p < 0.001). The gene discussed is CRP; the disease is clostridium difficile infection.