[Comparison of Scrub Typhus Cases Before and After the Revision of the Reporting Criteria]

Scrub typhus is a rickettsial infection caused by Orientia tsutsugamushi, with peak incidence during autumn in the Republic of Korea. To improve the accuracy of surveillance data and to assess the magnitude of recent infections, the Korea Disease Control and Prevention Agency revised the case definition on September 11, 2024. The updated definition requires both the presence of an eschar and a positive presumptive test result for clinical case reporting. This study examines the impact of this revision on case classification, diagnosis, and epidemiological trends.

To compare trends before and after the revision, we analyzed cases from September 11 to December 31 in 2022, 2023, and 2024, focusing on demographic characteristics, presence of eschar, and diagnostic methods. Monthly trends of suspected cases were also reviewed: 5,239 cases in 2024 and 52 provisional cases in January-April 2025.

According to the revised criteria, from September 11 to December 31, 2024, the proportion of suspected cases decreased by 12.5% compared to the same period of previous year, and cases with confirmed eschars increased by 1,235. From January to April 2025, the number of suspected cases declined by 86.4% compared to the previous year. Among the 236 patients without a visible eschar, 93 (39.4%) tested negative according to immunochromatographic assay/indirect immunofluorescence assay testing but positive according to polymerase chain reaction (PCR) testing, which led them to be classified as confirmed cases.

Revising the reporting criteria to include eschar confirmation improved diagnostic accuracy and compliance. The decrease in suspected cases during the non-epidemic season (January-March) contributed to a more accurate surveillance of recent infections. Eschar confirmation should be emphasized during presumptive diagnosis, and PCR testing should be conducted if an eschar is not identified.