The highest PCT values were observed for bacterial infection (median 8.4 ng/mL; IQR: 6.2–21.3), followed by viral infection (median 0.25 ng/mL; IQR: 0.1–0.71), and atypical infection (median 0.11 ng/mL; IQR: 0.08–0.16), while the CRP differed only between bacterial and viral pneumonia (median 264.3 mg/L versus 8.5 mg/L). Here, CRP is linked to viral infectious disease.