Scrub Typhus Workup

Updated: Apr 19, 2018
  • Author: David J Cennimo, MD, FAAP, FACP, FIDSA, AAHIVS; Chief Editor: Russell W Steele, MD  more...
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Workup

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. [34, 6] The hematologic manifestations may raise the suspicion of dengue infection. [32, 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. [34, 47] 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, 48]

Laboratory studies of choice are serologic tests for antibodies. The main confirmatory tests are the indirect immunoperoxidase test and the immunofluorescent assay. [49] 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. [50] 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. [51]

A study by Varghese et al that included 203 patients previously confirmed to have scrub typhus reported that IgM levels gradually declined but remained elevated above the diagnostic cutoff up to 12 months post-infection. [52]

O tsutsugamushi has been identified by means of the polymerase chain reaction (PCR) technique in clinical specimens. [53, 6, 54] Performing nested PCR on the eschar might be a rapid diagnostic test for scrub typhus in the early, acute stage. [55]

In 2007, Cao et al reported on the development of a rapid diagnostic reagent for scrub typhus. [56]

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, [28, 33] especially in the lower lung fields. [57]

Histologically, the basic pathologic change is focal or disseminated vasculitis caused by the destruction of endothelial cells and the perivascular infiltration of leukocytes. [58]