Dengue Outbreaks and Antibody Seroprevalence in Buenos Aires.

Buenos Aires, Argentina, a city with 3.1 million inhabitants, had a minimal prevalence of dengue until 2022, with nearly 25,000 cumulative reported cases. However, consecutive outbreaks in 2023 and 2024 significantly altered the epidemiological landscape, raising concerns about increasing viral circulation and a potential shift from a low-incidence, seasonal pattern toward more sustained transmission in this major urban setting. To assess the aftermath of the largest recorded dengue epidemic in Buenos Aires, we conducted a probabilistic, stratified, multistage serosurvey during the inter-epidemic period from August to October 2024. The study population consisted of 2.4 million adults, and dengue IgG and IgM antibodies were detected using a rapid immunoassay with an enzyme-linked fluorescence assay confirmation. Weighted seroprevalence reached 18.6% (95% CI: 15.6-21.5%) in 2024 (446,735 subjects). This represents a substantial increase in population immunity compared with previous estimates, likely reflecting the exceptional magnitude of the recent epidemic. The highest seropositivity rate was observed in informal settlements (38.1%), as well as in central (20.3%) and southern districts (21.3%), suggesting an uneven distribution of transmission risks. To the best of our knowledge, no previous seroprevalence studies in Argentina have directly assessed population immunity in the aftermath of a large-scale dengue outbreak, making this research particularly relevant. Our findings highlight a rapid shift in dengue virus circulation, underscoring the increasing vulnerability of Buenos Aires to dengue transmission. This surge in seroprevalence signals the need for strengthened vector control, improved surveillance, and targeted public health interventions, particularly in disadvantaged urban areas.