IL6 and clostridium difficile infection: Importantly, in CDI patients, serum levels of IL-6 and IL-23 (cytokines upstream of pathogenic Th17 cells) correlate with CDI severity.143,148 Patients with the highest serum levels of IL-6 (first quartile) were 7.6 times more likely to die from infection than those in the lowest quartile (p = .0009).