A serosurvey of Orientia tsutsugamushi from patients with scrub typhus |
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Authors: | D.M. Kim Y.-M. Lee J.-H. Back T.Y. Yang J.H. Lee H.-J. Song S.-K. Shim K.-J. Hwang M.-Y. Park |
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Affiliation: | 1. Division of Infectious Diseases, Departments of Internal Medicine and Research Center for Resistant Cells, School of Medicine, Republic of Korea;2. Haenam General Hospital, Haenam, Republic of Korea;3. Jangheung General Hospital, Jangheung, Republic of Korea;4. Department of Clincal Pathology, Gwangju Health College, Gwangju, Republic of Korea;5. Center for Disease Control and Prevention, National Institute of Health, Republic of Korea |
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Abstract: | Many countries where scrub typhus is endemic use their own cutoff values for antibody titres to differentiate between cured cases and current infections. To establish an antibody titre cutoff value, one needs to investigate the seroprevalence in endemic areas, and the duration of the increase in titre after complete cure. We conducted a follow-up study of anti-Orientia tsutsugamushi antibody titres using indirect immunofluorescence assays (IFA) and passive haemagglutination assays (PHA) in patients with scrub typhus. After the onset of symptoms, IgM antibody titres increased gradually over 2–3 weeks, peaked at about 4 weeks, and started to decrease rapidly between 4 and 5 weeks. At 1-year follow-up, the median IgM value was 1:10. Out of 77 patients who were tested at that time, 36 (47%) had IgM titres ≥1:20, and none had titres exceeding 1:80. Over the first 2 weeks, IgG antibody titres increased sharply, peaked at about 4 weeks and decreased rather gradually thereafter, with a median titre of 1:128 maintained up to the 18th month. At 1-year follow-up, five out of 77 patients (6.5%) had titres ≥1:1,024 and 57% had titres ≥1:128. Based on these results, a cutoff value of ≥1:160 for IgM antibody should differentiate between previous and current infections in endemic areas such as Korea and Japan, where scrub typhus occurs mainly in the autumn. |
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Keywords: | Antibodies indirect immunofluorescence assay PCR scrub typhus |
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