Clinical characteristics, laboratory findings, and risk factors for severe tick-borne encephalitis (TBE) in northeastern Poland: analysis of 1654 hospitalized cases between 1993 and 2023

Background: Tick-borne encephalitis (TBE) remains a growing public health challenge in Central and Eastern Europe.Northeastern Poland is among the regions with the highest incidence in Europe, yet data on long-term trends and predictors of severe disease are limited.Methods: We retrospectively analysed documentation of 1,654 patients hospitalized with TBE at the Medical University of Bialystok between 1993 and 2023.Cases were categorized as meningitis (M), meningoencephalitis (ME), or meningoencephalomyelitis (MEM).Demographic, clinical, and laboratory data were compared across groups, and logistic regression identified predictors of severe outcomes, intensive care admission, and sequelae.Results: M accounted for 50.1% of cases, ME for 41.9%, and MEM for 8.0%.MEM patients were older (median age 52 years) and more likely to develop neurological sequelae (43.6%) and require prolonged hospitalization (median 22 days).Independent predictors of severe disease included age >50 years (OR 2.32; 95% CI 1.85-2.91),elevated CSF protein concentration (OR 1.012 per mg/dL).Predictors of ICU admission or death included age >50 years, CSF pleocytosis >300 cells/L, and elevated CRP levels.None of the patients had completed a full TBE vaccination schedule.Conclusions: Older age, elevated CSF pleocytosis, high CRP are valuable early predictors of severe TBE.The high incidence of TBE in Poland and the low vaccination rate indicate the necessity of a more effective vaccination campaign.