Comparison of a rapid diagnostic test and microimmunofluorescence assay for detecting antibody to Orientia tsutsugamushi in scrub typhus patients in China

Objective: To evaluate the detection of IgM and IgG antibodies to Orientia tsutsugamushi (O. tsutsugamushi) by rapid diagnostic test (RBT) and microimmunofluoresence assay (mIFA). Methods: RDT using a mixture of recombinant 56-kDa proteins of O. tsutsugamushi and mIFA assay were performed on 20 patients from Fujian and 13 patients from Yunnan Province, and 82 sera samples from healthy farmers in Anhui Province and Beijing City in 2009. Comparison of the RDT and mIFA assay was performed by using chi(2) test and the P level of <0.05 was considered was to be significance. Results: Among these 82 normal sera samples, the specificity of R 100% for both Igm and IgG tests. In 33 samples from patients with scrub typhus, 5 cases were positively detected earlier by ROT than by mIFA in IgM test, and 2 cases were positive in IgG test. Sensitivities of ROT were 93-9% and 90.9% for IgM and IgG, respectively. The sensitivity of combination test of IgM and IgG was 100%. Geometric mean titer diluted sera from confirmed cases by IFA and ROT assay were 1 : 37 vs. 1 : 113 (P<0.001) in IgM test and 1 : 99 vs. 1 : 279 (P<0.05) in IgG test. Conclusions: RDT is more sensitivite than mIFA in the early diagnosis of scrub typhus and it is particularly applicable in rural areas.