also negatively correlated with SFTSV loads (*P* = 0.020, Figure [1f](#F1){ref-type="fig"}).

*PDGF-B* rs1800818 conferred no susceptibility to severe outcome in SFTS patients {#s2_5}
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Among the 1020 SFTS patients, 290 developed severe disease outcome, comprising 108 fatal cases. Compared with mild patients, significantly older age, more male gender and presence of underlying medical conditions were found in severe patients (Table [1](#T1){ref-type="table"}). Similar results were found when comparison was made between fatal and nonfatal patients (Table [1](#T1){ref-type="table"}). Comparison between severe patients vs. mild patients (OR = 0.87, 95% CI = 0.59-1.29; *P* = 0.48; Figure [2a](#F2){ref-type="fig"} and [Supplementary Table S3](#SD1){ref-type="supplementary-material"}) and fatal patients vs. nonfatal patients (OR = 0.91, 95% CI = 0.51-1.62; *P* = 0.75; Figure [2b](#F2){ref-type="fig"} and [Supplementary Table S4](#SD1){ref-type="supplementary-material"}) displayed no significant difference of the genotype frequencies for *PDGF-B* rs1800818 polymorphism after adjusting the effect from age, gender and underlying medical conditions by applying multivariate regression analysis. The PDGF-BB levels that were measured at acute infection in severe cases were comparable with mild cases (*P* = 0.45; Figure [2c](#F2){ref-type="fig"}). The PDGF-BB levels that were measured at acute infection in fatal cases were comparable with non-fatal cases as well (*P* = 0.96, Figure [2d](#F2){ref-type="fig"}).

![*PDGF-B* rs1800818 and PDGF-BB expression among severe fever with thrombocytopenia syndrome patients with different outcomes\
**a.** Genotype frequencies obtained from severe fever with thrombocytopenia syndrome (SFTS) patients with severe and mild disease. **b.** Genotype frequencies obtained from SFTS patients with fatal and nonfatal outcome. **c.** Serum PDGF-BB levels between mild SFTS patients and severe SFTS patients. **d.** Serum PD