Etiologies of acute undifferentiated fever and clinical prediction of scrub typhus in a non-tropical endemic area

• Published in: The American journal of tropical medicine and hygiene 2015-02, Vol.92 (2), p.256-261
• Main Authors: Jung, Ho-Chul, Chon, Sung-Bin, Oh, Won Sup, Lee, Dong-Hyun, Lee, Ho-Jin
• Format: Article
• Language: English
• Subjects: Acute Disease; Age Factors; Aged; Cross-Sectional Studies; Decision Support Techniques; Diagnosis, Differential; Emergency Service, Hospital - statistics & numerical data; Female; Fever - diagnosis; Fever - etiology; Fluorescent Antibody Technique, Indirect; Hepatitis A - diagnosis; Humans; Influenza, Human - diagnosis; Male; Middle Aged; Republic of Korea - epidemiology; Risk Factors; Scrub Typhus - diagnosis; Scrub Typhus - epidemiology; Scrub Typhus - etiology; Sensitivity and Specificity
• ISSN: 0002-9637; 1476-1645
• DOI: 10.4269/ajtmh.14-0377

Scrub typhus usually presents as acute undifferentiated fever. This cross-sectional study included adult patients presenting with acute undifferentiated fever defined as any febrile illness for ≤ 14 days without evidence of localized infection. Scrub typhus cases were defined by an antibody titer of a ≥ fourfold increase in paired sera, a ≥ 1:160 in a single serum using indirect immunofluorescence assay, or a positive result of the immunochromatographic test. Multiple regression analysis identified predictors associated with scrub typhus to develop a prediction rule. Of 250 cases with known etiology of acute undifferentiated fever, influenza (28.0%), hepatitis A (25.2%), and scrub typhus (16.4%) were major causes. A prediction rule for identifying suspected cases of scrub typhus consisted of age ≥ 65 years (two points), recent fieldwork/outdoor activities (one point), onset of illness during an outbreak period (two points), myalgia (one point), and eschar (two points). The c statistic was 0.977 (95% confidence interval = 0.960-0.994). At a cutoff value ≥ 4, the sensitivity and specificity were 92.7% (79.0-98.1%) and 90.9% (86.0-94.3%), respectively. Scrub typhus, the third leading cause of acute undifferentiated fever in our region, can be identified early using the prediction rule.