To select variables that predict severe influenza, patient characteristics (influenza type, age, duration of illness, sex, ethnicity, and bacterial status), and DEGs (MPO, PRTN3, ELANE, AZU1, BPI, CEACAM6, DEFA4, LCN2, CEACAM8, CTSG, RETN, OLFM4, RNASE3, DEFA3, MMP8, HP, DEFA1B, and LTF) were included in the LASSO regression analysis. The gene discussed is DEFA4; the disease is influenza.