A novel scoring system for precise severity quantification in severe fever with thrombocytopenia syndrome: development and application based on dynamic clinical data

Background Severe Fever with Thrombocytopenia Syndrome (SFTS) is an acute infectious disease with high mortality. This study aimed to develop a quantitative scoring system for grading SFTS severity using dynamic clinical data. Methods A retrospective study included 547 confirmed SFTS patients from two hospitals. Clinical data were collected over a 14-day course (divided into four phases). Patients were grouped into survivors ( n = 451) and non-survivors ( n = 96). Statistical analyses, including Kaplan–Meier curves and log-rank tests, were performed. A prospective external validation cohort of 44 newly diagnosed patients was subsequently enrolled to validate the scoring system using C-statistic, calibration curves, and decision curve analysis (DCA). Results Of 547 patients, 96 (17.55%) were non-survivors. Multivariate logistic regression identified six independent prognostic factors across phases: age, platelet (PLT), aspartate aminotransferase (AST), and creatinine (Cr) (days 5–7); age, red blood cell distribution width (RDW), Cr, and lactate dehydrogenase (LDH) (days 8–10); Cr and LDH (days 11–14). A scoring system (0–11 points) was developed, stratifying patients into low (0–3), intermediate (4–7), and high (8–11) risk groups, with adverse outcome rates of 1.04, 22.92, and 76.04%, respectively. Kaplan–Meier curves showed significant prognostic differences (log-rank p < 0.001). External validation (44 cases) confirmed excellent performance: AUC 0.810–0.952, good calibration (Hosmer-Lemeshow p > 0.05), and net clinical benefit (DCA Eavg 0.068–0.098, Emax 0.422–0.559). Conclusion A dynamic SFTS severity scoring system was developed and validated. Internal and external validation confirmed its reliability and clinical utility, providing a simple, practical tool for timely assessment and early intervention.