Abstract
BackgroundScrub typhus is a mite-borne infectious disease caused by Orientia tsutsugamushi. Few follow-up studies have assessed antibody titers using serologic tests from various commercial laboratories and the Korea Centers for Disease Control and Prevention (KCDC).MethodsA prospective study to assess the antibody titers in patients with scrub typhus and seroprevalence in individuals undergoing health checkups was conducted using results of immunofluorescence antibody assays (IFAs) and serologic tests, used by the KCDC and commercial laboratories, respectively. The following tests were performed simultaneously: (i) indirect IFA used by the KCDC to detect immunoglobulin (Ig) M and IgG, (ii) IFA used by a commercial laboratory to detect total Ig, and (iii) antibody tests using two commercially available kits.ResultsWhen the IgM and IgG cutoff values (≥1:16 and ≥1:256, respectively) used in the IFA and the total IgG cutoff values (≥1:40) were used in prospective follow-up investigations, the antibody positivity rates of 102 patients with scrub typhus were 44.1, 35.3, and 57.6%, respectively, within 5 days of symptom onset. Among 91 individuals who recovered from scrub typhus, the follow-up IgM, IgG, and total Ig positivity rates for 13 years were 37.4% (34/91), 22.0% (20/91), and 76.9% (70/91), respectively. Among 216 individuals undergoing health checkups, the seroprevalence of IgM was 4.2% (9/216); no seroprevalence of IgG was observed.ConclusionsIFAs used by the KCDC and the commercial laboratory and rapid commercial kits could not distinguish between patients who had recovered from scrub typhus and those who are currently infected with O. tsutsugamushi. In South Korea and other countries, where low antibody cutoff values are used, upward adjustments of cutoff values may be necessary.
Highlights
Scrub typhus is a mite-borne infectious disease caused by Orientia tsutsugamushi
Among 91 individuals who recovered from scrub typhus, the follow-up IgM, IgG, and total Ig positivity rates for 13 years were 37.4%
immunofluorescence antibody assays (IFAs) used by the Korea Centers for Disease Control and Prevention (KCDC) and the commercial laboratory and rapid commercial kits could not distinguish between patients who had recovered from scrub typhus and those who are currently infected with O
Summary
Scrub typhus is a mite-borne infectious disease caused by Orientia tsutsugamushi. Few follow-up studies have assessed antibody titers using serologic tests from various commercial laboratories and the KoreaCenters for Disease Control and Prevention (KCDC). Scrub typhus is a mite-borne infectious disease caused by Orientia tsutsugamushi. Few follow-up studies have assessed antibody titers using serologic tests from various commercial laboratories and the Korea. Scrub typhus is a vector-borne infectious disease caused by Orientia tsutsugamushi, which is transmitted by a chigger bite [1]. The most common method of diagnosing scrub typhus is serological tests; indirect immunofluorescence antibody assays (IFA), enzyme-linked immunosorbent assays, and passive hemagglutination assays are used to detect the presence of antibodies (Abs) against O. tsutsugamushi. These tests have limited clinical usefulness because antibodies are usually formed 1–2 weeks after infection [2].
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