Development of a scoring system to differentiate severe fever with thrombocytopenia syndrome from scrub typhus

<b>Abstract </b> Severe fever with thrombocytopenia syndrome (SFTS) and scrub typhus have similar clinical features, making it difficult to differentiate them. We retrospectively collected data from 183 SFTS and 178 scrub typhus patients and validated the prior scoring system to develop a more sensitive, specific, and objective scoring system. We first applied the prior scoring systems proposed by Kim et al. to differentiate SFTS from scrub typhus. After multivariable logistic regression, altered mental status, leukopenia, prolonged activated partial thromboplastin time (aPTT), and normal C-reactive protein (CRP) level (≤1.0 mg/dL) were significantly associated with SFTS.. We changed the normal CRP level ≤1.0 mg/dL to ≤3.0 mg/dL and replaced altered mental status with creatine kinase (CK). The modified scoring system showed 97% sensitivity and 96% specificity for SFTS (area under the curve (AUC): 0.983) and a higher accuracy than that of the original scoring system (P=0.0308). This study scoring system had 97% sensitivity and 98% specificity for SFTS (AUC: 0.992) and a higher accuracy than that of the original Kim’s scoring system (P=0. 0308). Our scoring system that incorporated leukopenia, prolonged aPTT, normal CRP level (≤3.0 mg/dL), and elevated CK level (&gt;1000 IU/L) easily differentiated SFTS from scrub typhus in an endemic area.