Tick-borne encephalitis seroprevalence in northern Italy: a cross-sectional study on a randomly selected population

Objectives: Ixodes ricinus is under-recognized in Europe. This study aimed to determine the seroprevalence and spatial distribution of tick-borne encephalitis (TBE) virus (TBEV) in areas close to endemic regions in Northern Italy. Methods: A multicenter study was conducted on a random sample of the general population afferent to hospitals in Veneto, Lombardy, and Piedmont with a pre-determined sample size of 1500 participants. The presence of TBEV-neutralizing antibodies was determined for sera positive to the TBE -specific immunoglobulin G test in a centralized laboratory. Results: Out of 1537 samples analyzed (790 from Lombardy, 394 from Veneto, 353 from Piedmont), 39 (2.5%) were immunoglobulin G TBEV-positive. The frequency of positive cases was similar amid the regions (24-3.0% Lombardy, 10-2.5% Veneto, and 5-1.4% Piedmont; P = 0.27). The seropositivity rates were 3.6% in subjects aged over 50 years, 2.0% in those aged 30-50 years, and 1.5% in subjects aged under 30 years ( P = 0.10). Two of them (one from Veneto and one from Lombardy) were confirmed by TBEV neutralization test (prevalence 130 per 100,000). One lived close to an endemic area (Treviso); the other spent time in an endemic region (Friuli) and did not remember experiencing tick bites. Conclusions: The results from this study highlight the need for raising awareness among the population and health care workers to limit the risk of TBE infection.