Francisella tularensis surveillance-infection-induced seroprevalences in Western Austria 2025.

BACKGROUND

Notified tularemia cases have been increasing in both the European Union and Austria, yet no contemporary seroprevalence data are available. This study aimed to estimate the current tularemia seroprevalence in Western Austria and to inform prevention programs by comparing seroprevalence-derived incidence rates with notified case numbers.

METHODS

Between December 2023 and February 2024, serum samples from 3008 healthy blood donors aged 18-70 years in Western Austria were collected and analyzed for anti-Francisella-tularensis-IgG-antibodies using a commercially available ELISA. In the absence of confirmatory serological assays, the manufacturer's cutoff values were increased to enhance specificity, as recommended by a previous serological evaluation.

RESULTS

Overall seroprevalence was 2.0% (95% confidence intervals, 95% CI 1.6-2.6), with comparable results in Vorarlberg and Tyrol. The 10-year mean notified incidence rate in Western Austria was 0.30/100,000/year, compared to 29/100,000/year based on seroprevalence data, indicating a substantial proportion of unreported infections (mean manifestation index of 1.05%). Seroprevalence varied markedly across districts, identifying potential tularemia hotspots.

CONCLUSION

Estimated annual tularemia incidence rates were substantially higher than notified case numbers, underscoring the need for public education, increased clinical awareness, and targeted prevention programs. The observed district-level variation in seroprevalence should be used to inform the geographic prioritization of such interventions.