In a study of 1608 patients with influenza pneumonia, patients with bacterial co-infection had significantly higher median PCT on admission than patients with no bacterial coinfection, with PCT of 4.35 ng/mL (IQR 0.6–19.9) versus 0.6 ng/mL (IQR 0.2–2.3), respectively, p = 0.001. This evidence concerns the gene CALCA and influenza.