Analysis of Laboratory Testing for Imported Dengue Fever in the Republic of Korea, 2020-2025.

Objectives: Dengue fever is an acute, mosquito-borne disease that is widely endemic in tropical and subtropical regions. While no autochthonous cases have been reported in the Republic of Korea, imported cases continue to occur. This study analyzed laboratory testing data from 2020 to 2025 to support the surveillance of imported mosquito-borne infections. Methods: A total of 2,904 laboratory test requests for dengue fever submitted to the Korea Disease Control and Prevention Agency and 17 provincial Institutes of Health and Environment were reviewed. Laboratory diagnosis was performed using real-time reverse transcription polymerase chain reaction (RT-PCR) and immunoglobulin M (IgM) enzyme-linked immunosorbent assay (ELISA). The analysis focused on annual trends, presumed countries of infection, and the distribution of dengue virus (DENV) serotypes. Results: Of the 2,904 test requests, 613 cases were confirmed positive, with an overall positivity rate of 21.1%. The number of positive cases was lowest in 2021, with three cases, but increased after international travel resumed, reaching 177 cases in both 2023 and 2024. Most infections were presumed to have been acquired in Southeast Asia, particularly in Indonesia, the Philippines, and Vietnam. DENV-2 was the most common serotype, followed by DENV-1, DENV-3, and DENV-4; all four serotypes were detected. Conclusions: Imported dengue fever increased following the recovery of international travel, with infections concentrated in Southeast Asia. Presumed countries of infection were mainly associated with four Southeast Asian countries (73.1%), with cases concentrated during the summer vacation season. Because reinfection with a different DENV serotype may increase the risk of severe dengue, individuals who travel repeatedly to dengue-endemic countries should exercise particular caution.