쯔쯔가무시병의 혈청학적 진단에서 교차반응에 대한 평가

Abstract

Background) Main serologic diagnostic tool of scrub typhus is immunofluorescence assay(IFA) that detect scrub typhus antibodies. However, the choice of cut-off values for diagnosis is complicated by factors such as antibody kinetics, geography, negative seroconversion and seasonality. (Method) Among total 253 consecutive patients with febrile disease enrolled in this study, 127 cases are within scrub typhus diagnosis criteria and rest of 126 cases are not. To determine the seroprevalence of antibody titer against Orientiatsutsugamushi, samples from 89healthy subjects who un derwent a health screening program extracted and than each samples titer was measured. The levels of serum scrub typhus antibody were measured by immunofluorescenceassay. (Result) IFA antibody titer in acute febrile patient group showed significantly high false positive rate(IgG 71.3%, IgM 65.9%) compared to low seroprevalance(IgG 6.7%, IgM 4.5%) in healty group. Higher false positive rate were showed especially in leptospirosis, HFRS, malaria, influenza carriers among acute febrile patients. But most acute febrile patients showed high false positive rate had been a decrease in antibody titer checked in follow-up samples instead of four fold increasing. It results that ideal cut-off value to diagnose scrub typhus for acute febrile patients is over 1:64 on lgG(sensitivity/specificity 67.5%/88.1%) and 1:16 on lgM(sensitivity/specificity 67.5%/88.1%) considering of antibody cross reactivity and remote scrub typhus infection. Particularly, over 1:128 on lgM indicated 100% specificity and it was possibly confirmed of scrub typhus. (Conclusion) Although IFA is standard to diagnose scrub typhus, it is difficult to make early diagnosis. But over 1:128 on IgM titer can be proposed as an useful cut-off value to diagnose scrub typhus in acute febrile patients. We also need to consider another diseases like leptospirosis or HFRS if antibody for scrub typhus is positive in acute febrile patients .