NLR, A Convenient Early-Warning Biomarker of Fatal Outcome in Patients With Severe Fever With Thrombocytopenia Syndrome

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that greatly threatens public health. This study aimed to examine a convenient early-warning biomarker of fatal outcomes in patients with SFTS to reduce mortality. Methods: A retrospective cohort study was performed, and patients with confirmed SFTS were enrolled in the top two hospitals in Anhui Province, China from 1 May 2016 to 31 October 2019. The clinical symptoms, laboratory indicators, and treatment data of patients with SFTS were evaluated. All patients with SFTS were followed up till 28 days from the start of admission. The laboratory indicators that could be used to predict the fatal outcome were identified. Results: A total of 228 patients with SFTS were enrolled, 177 patients were enrolled in the survival group, and 51 patients in the death group. The median age of all 228 patients with SFTS was 63 years. Five laboratory indicators (SFTSV viral load, neutrophil to lymphocyte ratio (NLR), aspartate transaminase (AST)/alanine aminotransferase (ALT), ALT, and blood urea nitrogen (BUN)) were identified as the predicting factors of the fatal outcome of patients with SFTS. The area under the receiver operating characteristic (ROC) curve (AUC) of SFTSV viral load was the highest (0.919), then NLR (0.849), followed by AST/ALT (0.758), AST (0.738), and BUN (0.709). The efficacy of SFTVS viral load and NLR in predicting fatal outcomes was significantly higher than AST/ALT, AST, and BUN. The Kaplan-Meier survival curves show that the case fatality rate was significantly increased in patients whose SFTSV viral load was higher than 500,000 or NLR higher than 2.0. Gamma-globulin treatment showed a significant difference between the survival group and the death group, and the duration of gamma-globulin that had been proposed should not be <3 days. Conclusion: The SFTSV viral load and NLR showed great efficacy in predicting the fatal outcome of patients with SFTS, and NLR is a convenient and efficient early-warning biomarker that helps healthcare workers focus on patients with high risks of fatal outcomes. The efficacy of gamma-globulin provided a new idea for the treatment of SFTS, which needs further analysis in future studies.