恙蟲病 SCRUB TYPHUS 診斷

FROM UPTODATE

http://www.uptodate.com/contents/scrub-typhus-clinical-features-and-diagnosis

早期幾乎沒有可靠的檢驗可以確診

嚴重病患幾乎都會出現血小板下降

GOT, BILIRUBIN Cr 上升

可能出現 LEUKOPENIA or LEUKOCYTOSIS, 但多數會正常

DIAGNOSIS — As with all rickettsial diseases, no laboratory test is diagnostically reliable in the early phases of scrub typhus. The disease is usually recognized when clinicians correlate the presence of compatible clinical signs, symptoms, and laboratory features, with epidemiologic clues (eg, recent exposure to environments in which chiggers are known or suspected to be present).

Patients with scrub typhus may develop the following laboratory abnormalities:

●Most patients with severe illness develop thrombocytopenia.

●Elevations in hepatic enzymes, bilirubin, and creatinine.

●Leukopenia or leukocytosis can occur, but most have a normal white blood cell count.

其他四種更精確診斷 SCRUB TYPHUS 的方法: 血清學, 切片, 培養, PCR. 

血清學檢驗

-- 相隔 14 天的血中 IFA 上升四倍以上

-- 單次 IFA 超過正常值  50 倍 (10倍~400倍) 

- - ELISA and passive hemagglutination assay.

-- Weil Felix test 不建議使用. 

While these laboratory findings are relatively nonspecific, four methods can be used to more definitively confirm the presence of O. tsutsugamushi infection: serology, biopsy, culture, and polymerase chain reaction.

Serology — The indirect fluorescent antibody (IFA) test remains the mainstay of serologic diagnosis. This test is available in most state health laboratories, which send the specimens to the Centers for Disease Control in Atlanta, GA. A battery of antigens from common strains of O. tsutsugamushi should be used to detect convalescent antibodies because of the organism's antigenic heterogeneity.

Among patients living in endemic areas, the serologic diagnosis of acute infection must be differentiated from background immunity against scrub typhus. A 2007 review made the following recommendations for diagnosis using the IFA assay [24]:

●A conclusive diagnosis of acute scrub typhus infection using the IFA assay should be based upon at least a fourfold increase in titer in paired samples drawn at least 14 days apart.

●A single measurement may be informative when there are locally validated criteria for a positive test. When a single measurement is performed, the most common cutoff titer is 1:50 (range 1:10 to 1:400).

A single measurement may also be used to make a preliminary diagnosis in travelers who live in areas in which scrub typhus is not endemic and who have recently returned from an endemic area [24]. However, only paired titers can make a definitive diagnosis [24,25].

An enzyme-linked immunosorbent assay and a passive hemagglutination assay have also been developed for the diagnosis of scrub typhus [26,27], and a dot blot immunoassay dipstick, which is undergoing clinical evaluation, may permit rapid diagnosis of scrub typhus [28]. The Weil Felix test, based upon a fortuitously discovered cross reaction between anti-rickettsial antibodies and Proteus antigens (OX2 and OX19), is neither specific nor sensitive. Thus, its use is no longer advised.

Biopsy of an eschar or generalized rash — The pathological hallmark of scrub typhus is a lymphohistiocytic vasculitis. Damage to endothelial cells occurs early in infection, leading to widespread vascular dysfunction. This endothelial injury causes a loss of vascular integrity, egress of plasma and plasma proteins, and microscopic and macroscopic hemorrhages. Thus, the histologic changes in biopsies of eschars include focal areas of cutaneous necrosis surrounded by a zone of intense vasculitis, with perivascular collections of lymphocytes and macrophages. Thrombosis of small blood vessels can also occur. Demonstration of these typical vasculitic changes can be diagnostic, even when rickettsiae are not demonstrable by fluorescent antibody conjugates.

只有少數實驗室有辦法培養.  

Culture — Culture of this organism is available in only a few centers. Specialized laboratory facilities with rigorous quality control and laboratory safety measures are required.

Polymerase chain reaction — PCR technology applied to the blood of patients with scrub typhus can definitively establish the diagnosis, even in the minority of patients who lack IgM antibodies early in the course of infection [29-31]. The sensitivity of a nested PCR assay using buffy coat preparations was 82 percent and the specificity was 100 percent in a study of 135 Korean patients with possible scrub typhus [31]. In addition to serum PCR, eschar PCR also appears to be a sensitive and specific assay for scrub typhus despite prior antibiotic treatment [32]. However, these tests are only available in specialized centers that have access to the required primers and laboratory facilities.