Performance of SD Bioline Tsutsugamushi Assays for the Diagnosis of Scrub Typhus in Thailand
Saowaluk Silpasakorn BSc*, Duangdao Waywa MSc*, Siriwan Hoontrakul MD**, Chuanpit Suttinont MD***, Kitti Losuwanaluk MD****, Yupin Suputtamongkol MD*
Affiliation : * Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand ** Chumphon Hospital, Chumphon, Thailand *** Maharat Nakhon Ratchasima Hospital, Nakhon Ratchasima, Thailand **** Banmai Chaiyapod Hospital, Burirum, Thailand
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
