Eosinophils and basophils in severe fever with thrombocytopenia syndrome patients: Risk factors for predicting the prognosis on admission

Background Severe fever with thrombocytopenia syndrome (SFTS) virus (SFTSV) is an emerging tickborne phlebovirus with a high fatality rate. Previous studies have demonstrated the poor prognostic role of eosinophils (EOS) and basophils (BAS) in predicting multiple viral infections. This study aimed to explore the role of EOS and BAS in predicting prognosis of patients with SFTS. Methodology A total of 194 patients with SFTS who were admitted to Yantai City Hospital from November 2019 to November 2021 were included. Patients' demographic and clinical data were collected. According to the clinical prognosis, they were divided into survival and non-survival groups. Independent risk factors were determined by univariate and multivariate logistic regression analyses. Findings There were 171 (88.14%) patients in the survived group and 23 (11.86%) patients in the non-survived group. Patients' mean age was 62.39 +/- 11.85 years old, and the proportion of males was 52.1%. Older age, neurological manifestations, hemorrhage, chemosis, and increased levels of laboratory variables, such as EOS% and BAS% on admission, were found in the non-survival group compared with the survival group. EOS%, BAS%, aspartate aminotransferase (AST), direct bilirubin (DBIL), and older age on admission were noted as independent risk factors for poor prognosis of SFTS patients. The combination of the EOS% and BAS% had an area under the curve (AUC) of (0.82; 95% CI: 0.725, 0.932, P = 0.000), which showed an excellent performance in predicting prognosis of patients with SFTS compared with neutrophil-to-lymphocyte ratio (NLR), and both exhibited a satisfactory performance in predicting poor prognosis compared with De-Ritis ratio (AST/alanine amino-transferase (ALT) ratio). EOS% and BAS% were positively correlated with various biomarkers of tissue damage and the incidence of neurological complications in SFTS patients. Conclusion EOS% and BAS% are effective predictors of poor prognosis of patients with early-stage SFTS. The combination of EOS% and BAS% was found as the most effective approach. Author summary Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by a novel phlebovirus (SFTS virus, SFTSV), which has a wide range of clinical manifestations, from hyperthermia, thrombocytopenia, leukopenia, and gastrointestinal symptoms to hemorrhage, altered consciousness, and multiple organ dysfunction. It has a high mortality rate of about 11-30%. There is no specific treatment for SFTS, thus it is urgent to concentrate on patients infected with SFTSV and to identify the associated risk factors to reduce the number of critically ill and fatal cases. In the present study, EOS% and BAS% were for the first time used as variables to predict clinical outcomes of early-stage SFTS patients. The combination of EOS% and BAS% exhibited a satisfactory predictive performance compared with previously reported measures related to clinical outcomes. We also found that EOS% and BAS% were associated with neurological symptoms and signs. This study contributed to the risk factors findings on SFTS, which will be useful as guidelines for identifying the critical patients with SFTS.