Korat‐Scrub Typhus Score: A Clinical Tool for Predicting Scrub Typhus in Patients With Acute Undifferentiated Febrile Illness

OBJECTIVE: Scrub typhus is a major cause of acute undifferentiated febrile illness (AUFI) in the Asia-Pacific region. Nonspecific presentation, limited diagnostic accuracy and delayed treatment increase morbidity and mortality. This study aimed to develop a simple clinical score for early diagnosis in adults with AUFI. METHODS: A cross-sectional study of adults (≥ 18 years) with AUFI was conducted at a tertiary hospital in northeastern Thailand from June 2021 to May 2022. The Korat-Scrub Typhus Score was developed by analysing all clinically relevant variables using multivariable logistic regression with backward stepwise selection. Model performance was assessed using the Hosmer-Lemeshow goodness-of-fit test and the area under the receiver operating characteristic curve (AUC), with internal validation via 1000 bootstrap replications. RESULTS: Among 366 AUFI patients, 75 had scrub typhus. Most were male (66.7%), with mean age of 53.6 ± 17.6 years and median illness duration of 4 days (IQR 2-7). Five predictors were identified: outdoor activities, rash (excluding eschar), headache, abnormal chest radiograph findings and aspartate aminotransferase ≥ 100 U/L. The Korat-Scrub Typhus Score (0-13) stratified risk into low (< 5), moderate (5-6) and high (> 6) groups, with likelihood ratios of 0.55 (95% CI, 0.43-0.71), 2.20 (95% CI, 1.37-3.53) and 9.22 (95% CI, 4.19-20.25), respectively. The model showed good calibration, acceptable discrimination (AUC = 0.783, 95% CI 0.725-0.842) and minimal overfitting after internal validation. CONCLUSION: Scrub typhus is a common cause of AUFI. The Korat-Scrub Typhus Score uses simple clinical and laboratory data to support early diagnosis and timely treatment.