Diagnostic performance of PCT at the 500 pg/mL cut-off on day 2 after onset of fever in i) documented infections (MDIB, MDInB and CDI) vs. FUO, ii) non-CNS MDIB, non-CNS MDInB and deep-seated CDI vs. FUO, and iii) non-CNS MDIB vs. FUO. The gene discussed is CALCA; the disease is clostridium difficile infection.