The endothelial biomarkers clearly separated the pathogen-specific disease groups on the PCA plot (Figure 3c), with the angiopoietins, PDGFs and P-selectin driving the separation on PC1 of patients with COVID-19 from the others (ANOVA P<0·001, Games-Howell P<0·05 for COVID-19 versus CAP-strep and P<0·001 for COVID-19 versus CAP-flu), whereas PC2 separated viral from non-viral pneumonia mainly by syndecan-1 and E-selectin (ANOVA P<0·01, Games-Howell P<0·05 for CAP-flu versus CAP-strep, and P<0·01 for COVID-19 versus CAP-strep). Here, SDC1 is linked to viral pneumonia.