Isolation of Orientia tsutsugamushi from Human Blood and Factors Effect In Vitro Isolation in South Korea

Introduction: Orientia tsutsugamushi, the causative agent of scrub typhus, is endemic to South Korea. While diagnostics such as PCR and immunochromatographic tests (ICT) are widely used, pathogen isolation remains essential for antimicrobial resistance and genetic studies. Methods: In this study, 444 blood samples were collected from febrile patients across 13 hospitals. Among 263 samples identified as scrub typhus-positive by at least one diagnostic method, 99 isolates were successfully cultured. Fisher's exact test and the Wilcoxon rank-sum test were used to estimate odds ratios. Results: A positive nested PCR result (odds ratio [OR] = 28.85), clinician's diagnosis (OR = 16.33), and presence of eschar (OR = 10.95) were strongly associated with successful isolation. Furthermore, delays from blood collection to inoculation significantly impacted outcomes: Isolation success was 41.4% when inoculated within 2 days, but declined to 15.0% after ≥8 days. Conclusions: These findings underscore the importance of prompt sample handling and key clinical indicators in improving O. tsutsugamushi isolation efficiency for downstream research applications.