A serosurvey of Orientia tsutsugamushi from patients with scrub typhus

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 > or =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 > or =1:1,024 and 57% had titres > or =1:128. Based on these results, a cutoff value of > or =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.

Use of Multiplex Real-Time PCR To Diagnose Scrub Typhus

“…However, 22 additional patients with inconclusive IFA results could be diagnosed by PCR. Thus, the sensitivity of the dynamic serology criterion in this study was 52/74 or approximately 70%, which is comparable to that of previous studies (7,27). Combining the PCR and IFA titers of the paired sera will increase the diagnostic sensitivity without compromising specificity.…”

“…Although IFA is considered the gold standard test because of its high (96% to 98%) specificity (6, 7), its sensitivity is only approximately 60% to 80% (7,27). The low sensitivity of the diagnostic criterion using a 4-fold increase in the titer of paired sera is likely due to the serotypic diversity of O. tsutsugamushi organisms and inappropriate timing of specimen collection (7).…”

“…Therefore, the cutoff value of an IgM titer of Ն1:400 is appropriate for the area of this study. However, some experts in different areas of endemicity may use a different cutoff value, depending on the local evidence (5,27). Since severe scrub typhus may present with clinical manifestations of sepsis (28), broad-spectrum antimicrobial treatment is usually prescribed to these patients.…”

Seroprevalence of Scrub typhus at a tertiary care hospital in Andhra Pradesh

“…Weil-Felix is a commonly used inexpensive serological test which lacks both sensitivity and specifi city. [25] There is need for a rapid, technically simple and economic test. ELISA is an easy and comparatively economic test but the results of this test may not be available on the same day as samples need to be pooled for testing thus causing delayed diagnosis and treatment, which at times may be fatal.…”

Etiologies of Acute Undifferentiated Fever and Clinical Prediction of Scrub Typhus in a Non-Tropical Endemic Area

“…Patients who showed either an IFA antibody titer of 1:160 in a single serum or a positive result of an immunochromatographic test for O. tsutsugamushi were defined as possibly having scrub typhus. 17,18 In Korea, IFA was mostly performed in a commercial laboratory to measure the levels of total antibodies (immunoglobulin G [IgG], IgM, and IgA) against the standard O. tsutsugamushi antigens from the Gilliam, Karp, and Boryong strains. Immunochromatographic test was performed in each hospital to detect antibodies against 56-kDa major surface protein antigens from representative strains using commercial kits (SD Bioline Tsutsugamushi Assay; Standard Diagnostics, Yongin, Korea).…”