A Prospective Evaluation of Real-Time PCR Assays for the Detection of Orientia tsutsugamushi and Rickettsia spp. for Early Diagnosis of Rickettsial Infections during the Acute Phase of Undifferentiated Febrile Illness

One hundred and eighty febrile patients were analyzed in a prospective evaluation of Orientia tsutsugamushi and Rickettsia spp. real-time polymerase chain reaction (PCR) assays for early diagnosis of rickettsial infections. By paired serology, 3.9% (7 of 180) and 6.1% (11 of 180) of patients were confirmed to have acute scrub or murine typhus, respectively. The PCR assays for the detection of O. tsutsugamushi and Rickettsia spp. had high specificity (99.4% [95% confidence interval (CI): 96.8–100] and 100% [95% CI: 97.8–100], respectively). The PCR results were also compared with immunoglobulin M (IgM) immunofluorescence assay (IFA) on acute sera. For O. tsutsugamushi, PCR sensitivity was twice that of acute specimen IgM IFA (28.6% versus 14.3%; McNemar's P = 0.3). For Rickettsia spp., PCR was four times as sensitive as acute specimen IgM IFA (36.4% versus 9.1%; P = 0.08), although this was not statistically significant. Whole blood and buffy coat, but not serum, were acceptable specimens for these PCRs. Further evaluation of these assays in a larger prospective study is warranted.