title: Etiologies of acute undifferentiated fever and clinical prediction of scrub typhus in a non-tropical endemic area.
abstract: 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.
authors.affiliation: Department of Internal Medicine, Kangwon National University School of Medicine, Chuncheon, Republic of Korea; Department of Emergency Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Ho-Chul
authors.initials: HC
authors.lastname: Jung
authors.affiliation: Department of Internal Medicine, Kangwon National University School of Medicine, Chuncheon, Republic of Korea; Department of Emergency Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Sung-Bin
authors.initials: SB
authors.lastname: Chon
authors.affiliation: Department of Internal Medicine, Kangwon National University School of Medicine, Chuncheon, Republic of Korea; Department of Emergency Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea onesbi@gmail.com.
authors.forename: Won Sup
authors.initials: WS
authors.lastname: Oh
authors.affiliation: Department of Internal Medicine, Kangwon National University School of Medicine, Chuncheon, Republic of Korea; Department of Emergency Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Dong-Hyun
authors.initials: DH
authors.lastname: Lee
authors.affiliation: Department of Internal Medicine, Kangwon National University School of Medicine, Chuncheon, Republic of Korea; Department of Emergency Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Ho-Jin
authors.initials: HJ
authors.lastname: Lee
mesh_terms: D000208:Acute Disease; D000367:Age Factors; D000368:Aged; D003430:Cross-Sectional Studies; D003661:Decision Support Techniques; D003937:Diagnosis, Differential; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data; D005260:Female; D005334:Fever / Q000175:diagnosis / Q000209:etiology*; D019084:Fluorescent Antibody Technique, Indirect; D006506:Hepatitis A / Q000175:diagnosis; D006801:Humans; D007251:Influenza, Human / Q000175:diagnosis; D008297:Male; D008875:Middle Aged; D056910:Republic of Korea / Q000453:epidemiology; D012307:Risk Factors; D012612:Scrub Typhus / Q000175:diagnosis* / Q000453:epidemiology / Q000209:etiology; D012680:Sensitivity and Specificity