Silent Spread of Borrelia Infection in Sardinia, Italy: Implications for Integrated Surveillance in the Mediterranean

<b>Background</b>: Lyme borreliosis (LB) constitutes a major challenge for Public Health, particularly in regions where surveillance and diagnostic systems are underdeveloped or fragmented. Despite its potential as a hotspot for tick-borne diseases, Sardinia (Italy) remains poorly explored in terms of LB epidemiology. <b>Methods</b>: A sero-prevalence study was conducted on serum samples stored in the biobank of a hospital in Northern Sardinia. The serum library consisted of serum samples collected on the basis of a diagnostic hypothesis of rheumatic disease. Serological testing for antibodies against <i>Borrelia</i> was performed using the indirect immunofluorescence assay (IFA) and enzyme-linked immunosorbent assays (ELISA), followed by confirmation by Western blot for positive results. The study analyzed 58 serum samples from patients selected based on clinical symptoms compatible with <i>Borrelia</i> spp. infection. <b>Results</b>: Among the 58 patients, 9 (15.5%) yielded positive results, with absorbance values higher than those of the positive control, suggesting that the pathogen is widespread but poorly recognized in Sardinia. The results are in line with broader trends in the Mediterranean, indicating that Sardinia can no longer be considered a marginal area for <i>Borrelia</i> spp. circulation. <b>Conclusions</b>: The status of Sardinia as a sentinel territory underlines the need for enhanced epidemiological surveillance within the One Health approach, including human, animal and environmental health.