An autochthonous outbreak of dengue in Spain in 2024

INTRODUCTION: Autochthonous dengue transmission is increasingly being reported in temperate regions of Europe, particularly in areas with established Aedes albopictus populations and high population mobility. We describe a locally acquired dengue outbreak identified in Vila-seca (Tarragona, north-eastern Spain), which involved eight confirmed cases, two of which were asymptomatic, and the associated public health response. MATERIALS AND METHODS: Following the notification of two non-travel-associated dengue cases in September 2024 at Hospital Universitari de Tarragona Joan XXIII, epidemiological, virological, and entomological investigations were conducted led by Public Health Agency of Catalonia with the collaboration of microbiology departments of Hospital Universitari Vall d'Hebron and Hospital Clínic of Barcelona. Active case finding, contact tracing, laboratory confirmation, viral sequencing, and vector surveillance were implemented in the affected area of Vila-seca (Spain). RESULTS: A total of eight confirmed dengue cases were identified. The index cases were two residents without travel history who presented with fever, rash, and myalgia and tested positive for dengue virus (DENV). Four additional cases were detected through active surveillance, including three household contacts employed at a nearby entertainment resort and one resident living approximately 160 meters from the index household. Two further epidemiologically linked cases were identified among French tourists following international alerts. All patients recovered, and no additional cases were detected after November 2024, coinciding with decreased vector activity. Virological analysis confirmed local transmission of DENV-1, genotype V (clade D.2). Entomological surveys demonstrated widespread Ae. albopictus presence in public and private settings, prompting immediate vector control interventions, although no infected mosquitoes were detected. CONCLUSION: This outbreak illustrates the growing risk of DENV transmission in non-endemic European settings with intense tourist and occupational mobility. Rapid diagnostics, genomic surveillance, coordinated vector control, and timely international communication are essential to limit transmission and protect both residents and travellers, reinforcing the importance of a One Health approach.