Seroprevalence of Borrelia burgdorferi sensu lato and incidence of Lyme borreliosis in Switzerland.

Lyme borreliosis (LB), caused by Borrelia burgdorferi sensu lato (Bbsl), is a significant public health concern in Switzerland. Reliable data on seroprevalence and incidence are needed to better understand disease burden and inform prevention strategies. This study aimed to estimate the seroprevalence of Bbsl-specific antibodies and the incidence of symptomatic LB infections in the Swiss adult population. We analyzed Bbsl-specific IgG antibodies in 2,194 residual plasma samples from blood donors (aged 18-75 years) collected at seven Swiss Red Cross donation centers between September and December 2022. Samples were tested using the Liaison® Borrelia IgG VlsE chemiluminescence immunoassay and confirmed with the SeraSpot Anti-Borrelia-10 IgG assay according to National Reference Laboratory interpretative criteria. The overall seroprevalence was 6.1%, with higher prevalence in males (8.2%) than in females (2.9%) and regional variation ranging from 1.6% in Genève to 8.8% in Bern. Based on seroprevalence data, the estimated incidence of symptomatic Bbsl infections was 224 cases per 100,000 population per year (PPY). This estimate, although 1.3 times higher, is similar to the incidence derived from the Sentinella surveillance network. Using Sentinella data, clinically diagnosed erythema migrans was the most common manifestation (150 cases per 100,000 PPY), while disseminated forms, confirmed by clinical and laboratory criteria, occurred less frequently (1.0-8.5 cases per 100,000 PPY). Our findings provide critical insights into the burden of LB in Switzerland, highlight its public health relevance, and reinforce the importance of preventive measures. Future research should focus on longitudinal monitoring and harmonized methodologies to facilitate cross-country comparisons.