CRP and infection: Firstly, the area under the receiver operating characteristic (ROC) curve (AUC) statistic showed that the FCBI-index had an AUC of 0.901 (95% CI: 0.874–0.927), superior to that of CRP (AUC = 0.815, 95% CI: 0.777–0.853) and PCT (AUC = 0.715, 95% CI: 0.669–0.762) in distinguishing between microbiologically confirmed bacterial (n = 193) and viral (n = 291) infections (see the table associated with Fig. 3b).