Dengue Seroprevalence Among Blood Donors in the Lazio Region (Italy): Is There an Iceberg Beneath the Surface?

During 2023, dengue virus (DENV) autochthonous circulation was detected in Lazio, Italy. To investigate the magnitude of the phenomenon, anti-DENV serological status of blood donors residing in previously affected Rome municipalities was evaluated. Between December 2024 and April 2025, blood donors consecutively accessing to the seven recruited transfusion medicine units in the Lazio region (Italy) were screened for enrollment. Anti-DENV IgG antibodies were assessed using a commercial ELISA assay (EUROIMMUN, Germany), and positive results were confirmed by virus neutralization (VNT). A total of 1297 consecutive blood donors were enrolled. None reported having a previous diagnosis of dengue. Six came from endemic countries. Initial ELISA screening identified 22 samples (18 positive and 4 equivocal) that were further investigated by VNT. Anti-DENV neutralizing antibodies were confirmed in 7 donors, with a 0.54% prevalence rate (7/1297; 95% CI 0.14-0.94). Only 1 out of the 7 donors with confirmed presence of anti-DENV IgG denied a history of travels to endemic areas. The prevalence of donors with possible local transmission was 0.08% (95% CI: 0.01-0.44). The study suggests that undetected viral circulation in the Lazio region is very unlikely, and the rate of mild or asymptomatic infections may be lower than that reported in endemic countries.