Nationwide epidemiology of laboratory-confirmed Vibrio and Shewanella infections in Denmark, 2019–2025

Vibrio and Shewanella infections are climate-sensitive marine bacterial infections of increasing public health relevance in northern Europe, particularly in areas with brackish or low-salinity waters. Previous nationwide Danish data described infection patterns through 2018, but registry-linked severity outcomes and a standardised episode-based baseline for routine surveillance have not been described. We characterised laboratory-confirmed infections in Denmark during 2019–2025 and established an epidemiological baseline for national surveillance. We conducted a nationwide registry-linked study using the Danish Microbiology Database linked to demographic, geographical, hospitalisation and mortality registries. Infection episodes were constructed using a six-month algorithm applied separately by species, and one representative specimen category was selected per episode using a predefined hierarchy. We described species, specimen categories, seasonality, travel history, geographical distribution, hospitalisation and all-cause mortality within 30 days. We identified 1,181 infection episodes, including 680 Vibrio and 501 Shewanella episodes. Episodes were concentrated in June-September, particularly for V. vulnificus (31/32; 97%), V. parahaemolyticus (184/217; 85%), S. algae (234/298; 79%) and V. alginolyticus (171/241; 71%). Wound or soft-tissue specimens were most common (564/1,181; 48%). V. vulnificus had the highest proportion of blood/invasive or deep-tissue specimens (18/32; 56%) and hospitalisation (22/32; 69%). Overall, 183 episodes (15%) involved hospitalisation and 13 (1%) were followed by death within 30 days. Cumulative incidence was highest in several coastal and island municipalities. Registry linkage provided severity indicators beyond microbiological infection patterns and identified V. vulnificus as the species most frequently associated with invasive or deep-tissue specimens and hospitalisation. Shewanella accounted for a substantial proportion of episodes, supporting its inclusion alongside Vibrio in routine surveillance. The standardised episode-based approach provides a national baseline for MiBa-based surveillance implemented from 2026, informs preparedness, and may inform surveillance of marine bacterial infections in other northern European coastal settings.