Clinical usefulness of eschar polymerase chain reaction for the diagnosis of scrub typhus: a prospective study.

Background: The aim of this study was to determine the diagnostic utility of performing eschar polymerase chain reaction (PCR) for the diagnosis of scrub typhus through a prospective comparison of eschar PCR results with indirect immunofluorescent antibody assay (IFA) results.

Methods: We conducted a multicenter prospective study involving patients with possible scrub typhus. Whole-blood samples and eschars were obtained for serological evaluation and PCR. A new crust was formed several days later at the site of the removed eschar. The newly formed crust was taken for performance of the second eschar PCR. Additional blood samples and eschars were collected, if possible, at 1-week intervals for 1 month after antibiotic treatment.

Results: We prospectively studied 135 patients with possible scrub typhus. Of these patients, 118 had scrub typhus confirmed on the basis of either a single indirect immunofluorescent specific immunoglobulin M titer against Orientia tsutsugamushi of > or = 1:10 or a > or = 4-fold increase in the follow-up titer. The results of nested PCR assay of the eschars demonstrated a sensitivity of 0.86 (95% confidence interval, 0.78-0.92) and a specificity of 1 (95% confidence interval, 0.05-1). Among the 50 patients who showed positive results of eschar PCR at admission, 46 (92%) also showed positive results for the follow-up PCR test of the newly formed eschar after the treatment with antibiotics.

Conclusions: The eschar PCR assay was useful as a rapid and reliable test to confirm the diagnosis of scrub typhus, even though the patients received treatment with appropriate antibiotics, such as macrolides, quinolones, and tetracycline, which are all active against Orientia and Rickettsia species.