Plasma SFTS viral load and antibody titer in patients with SFTS. Both segment S (seg S) and M (seg M) titers were significantly higher in non-survivors than in survivors and increased during hospitalization (A,B). The SFTS viral load (hospital days 1–2) was significantly higher in non-survivors (D,E). The plasma antibody titer against SFTSV increased in survivors during hospitalization but decreased in non-survivors (C). There were no differences between the initial (hospital days 1–2) anti-SFTSV-IgG titers of the survivors and non-survivors (F). Blue, survivor; red, non-survivor. ** p < 0.01, *** p < 0.001, **** p < 0.0001.