Spatial and seasonal determinants of Lyme borreliosis incidence in France, 2016 to 2021

Background: Lyme borreliosis (LB) is the most wide-spread hard tick-borne zoonosis in the northern hemisphere. Existing studies in Europe have focused mainly on acarological risk assessment, with few investigations exploring human LB occurrence. Aim: We explored the determinants of spatial and seasonal LB variations in France from 2016 to 2021 by integrat-ing environmental, animal, meteorological and anthro-pogenic factors, and then mapped seasonal LB risk predictions. Methods: We fitted 2016-19 LB national surveillance data to a two-part spatio-temporal sta-tistical model. Spatial and temporal random effects were specified using a Besag-York-Mollie model and a seasonal model, respectively. Coefficients were estimated in a Bayesian framework using integrated nested Laplace approximation. Data from 2020-21 were used for model validation. Results: A high vege-tation index (>= 0.6) was positively associated with sea-sonal LB presence, while the index of deer presence (> 60%), mild soil temperature (15-22 degrees C), moderate air saturation deficit (1.5-5 mmHg) and higher tick bite frequency were associated with increased incidence. Prediction maps show a higher risk of LB in spring and summer (April-September), with higher incidence in parts of eastern, midwestern and south-western France. Conclusion: We present a national level spa-tial assessment of seasonal LB occurrence in Europe, disentangling factors associated with the presence and increased incidence of LB. Our findings yield quantitative evidence for national public health agen-cies to plan targeted prevention campaigns to reduce LB burden, enhance surveillance and identify further data needs. This approach can be tested in other LB endemic areas.