Objective: To assess the diagnostic capacity of a commercially available test (SD Bioline Tsutsugamushi assay) to aid with the diagnosis of scrub typhus in febrile patients in Thailand.
Material and Method: A commercially available lateral-flow-format immunochromatographic test (ICT) for the detection of O. tsutsugamushi IgM, IgG and IgA antibodies was evaluated, using archived serum samples from 102 laboratory confirmed scrub typhus patients and from 63 patients with other causes of fever as the negative control.
Results: The sensitivity, specificity of this rapid immunochromatographic test were 66.7% (95% CI, 57.1 to 75.1%) and 98.4% (95% CI 91.5 to 99.7%) respectively. False positive ICT result occurred in one patient with influenza A infection.
Among patients with scrub typhus, 17 out of 38 patients (44.7%, 95% CI 30.2 to 60.3%) with negative IgM antibody test by IFA (titer < 1:50) had positive ICT test. Compared to IFA IgG, 33 out of 54 patients (66.1%, 95% CI 47.8 to 72.9%) with negative IgG antibody test by IFA (titer < 1:50) had positive ICT test.
Conclusion: This rapid ICT test for the diagnosis of scrub typhus was more sensitive than the standard IFA in acute phase specimens.

Keywords: Immunochromatographic assay, Scrub typhus