Multi-country occurrence of non-cholera Vibrio infections in the Nordic countries and countries bordering the Baltic Sea in 2018

Background. Northern European countries and countries bordering the Baltic Sea have witnessed an increase of vibriosis cases during recent heatwaves. Here, we described the epidemiology of vibriosis cases and the genetic diversity of Vibrio isolates from seven countries in the region during 2018, which had an exceptionally warm summer.Methods. We conducted a retrospective study and analysed demographics, geographic distribution, seasonality, causative species, and severity of non-travel related vibriosis cases in 2018. Moreover, we carried out whole genome sequencing of isolates from 2014-2018 to investigate their phylogenetic relatedness, virulence and antimicrobial resistance profiles.Findings. We identified 1055 cases of vibriosis in the study countries between 2014-2018 of which 445 (42·2%) occurred in 2018 alone. The main reported mode of transmission was exposure to seawater. We observed a species-specific geographic disparity of vibriosis cases across the Nordic-Baltic region. Developing severe vibriosis was associated with infections caused by Vibrio vulnificus or Vibrio parahaemolyticus, being =65 years of age or acquiring infections during summer. Although phylogenetic analysis revealed diversity between Vibrio isolates, two V. vulnificus clusters (<10 SNPs) were identified in Norway and Sweden. Common Vibrio virulence and antimicrobial resistance determinants were found in several isolates.Interpretation. Numbers of vibriosis cases are increasing and represent a public health threat. Therefore, it is important to develop laboratory capacity, introduce and harmonise vibriosis surveillance within and between countries as well as create awareness campaigns.