We also found that properdin positivity in the COVID-19 group (2.25 [0.02%–9.47%]) was significantly higher than that in control (0.21% [0.01%–1.66%], P < 0.001) or bacterial sepsis group (0.74% [0.09%–3.91%], P = 0.001) (Figure 1a). The gene discussed is CFP; the disease is COVID-19.