Scrub Typhus Workup

Updated: Oct 01, 2015
  • Author: David J Cennimo, MD, FAAP, FACP, AAHIVS; Chief Editor: Russell W Steele, MD  more...
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Approach Considerations

Routine laboratory studies in patients with scrub typhus reveal early lymphopenia with late lymphocytosis. A decrease in the CD4:CD8 lymphocyte ratio may also be noted. Thrombocytopenia is also seen. [33, 6] The hematologic manifestations may raise the suspicion of dengue infection. [31, 3]

Elevated transaminase levels may be present in 75-95% of patients. Hypoalbuminemia occurs in about 50% of cases, whereas hyperbilirubinemia is rare. These findings may be especially prevalent in children. [33, 46] In adults, elevated transaminase levels relate to severity of disease. [11, 6] Transaminitis combined with other symptoms and exposure history may suggest possible leptospirosis. Coinfection with leptospirosis has been reported. [3, 47]

Laboratory studies of choice are serologic tests for antibodies. The main confirmatory tests are the indirect immunoperoxidase test and the immunofluorescent assay. [48] An infection is confirmed by a 4-fold increase in antibody titers between acute and convalescent serum specimens. A single high titer with classic clinical features is considered a probable case. Serology for all suspected subtypes should be requested. [6]

The indirect fluorescent antibody test is sensitive and provides results in a couple of hours. [49] It uses fluorescent antihuman antibody to detect specific antibody from patient serum bound to a smear of scrub-typhus antigen. A dot immunoassay has also been used in the serodiagnosis of scrub typhus.

A study of 2 rapid immunochromatographic tests for detection of IgM and IgG against O tsutsugamushi determined that both assays were more sensitive and specific than the standard immune immunofluorescence assay for the early diagnosis of scrub typhus. [50]

O tsutsugamushi has been identified by means of the polymerase chain reaction (PCR) technique in clinical specimens. [51, 6, 52] Performing nested PCR on the eschar might be a rapid diagnostic test for scrub typhus in the early, acute stage. [53]

In 2007, Cao et al reported on the development of a rapid diagnostic reagent for scrub typhus. [54]

The Weil-Felix OX-K strain agglutination reaction can be used to aid in diagnosis of scrub typhus. It may be the only serologic test available in less developed countries; unfortunately, it is not a very sensitive assay. [3]

Chest radiography may reveal pneumonitis, [27, 32] especially in the lower lung fields. [55]

Histologically, the basic pathologic change is focal or disseminated vasculitis caused by the destruction of endothelial cells and the perivascular infiltration of leukocytes. [56]