Oropouche virus attack rate in an urban setting outside the Amazon Basin: findings from a post-outbreak seroprevalence survey

Summary: Background: Oropouche virus (OROV) is transmitted by the biting midge Culicoides paraensis . Historically, it was restricted to small outbreaks in the Amazon region. Since 2023, genomic reassortment and human–environment interactions facilitated its geographic expansion, including into urban areas. We estimate the OROV attack rate and identify factors associated with infection in an urban area outside the Amazon.

Methods

A randomised cross-sectional serosurvey in the urban area of Baturité, Brazil. Households were selected using stratified probability sampling proportional to census tract population; one resident per household was randomly chosen. Participants completed a questionnaire, and serum samples were tested for OROV IgM using MAC-ELISA. Associations were estimated using prevalence ratios (PR) with 95% confidence intervals from Poisson regression with robust variance. Spatial clustering of seropositives was assessed using kernel density and nearest-neighbours.