Severe CDI was defined with a white blood cell (WBC) count >15,000 per microliter within 48 h of CDI diagnosis as previously described.18 Significant increases in serum and fecal IL-27 protein concentrations were observed in CDI-positive patients when compared to CDI-negative patients (Supplementary Figure S1A). The gene discussed is IL27; the disease is clostridium difficile infection.