In this respect, it is noteworthy that there is growing evidence suggesting that the host immune response is an important predictor of clinical severity and adverse outcomes in CDI patients (Kelly and Kyne, 2011; El Feghaly et al., 2013b; Yu et al., 2017)—for instance, fecal C-X-C motif chemokine 5 (CXCL5) and interleukin (IL)-8, not bacterial burden, were correlated with clinical severity in CDI patients (El Feghaly et al., 2013a). The gene discussed is CXCL5; the disease is clostridium difficile infection.