Long-Term Outcomes in Adult Patients with Tick-Borne Encephalitis in Latvia

Background: Tick-borne encephalitis (TBE) is an endemic neuroinfectious disease prevalent in parts of Europe and is often associated with persistent neurological and cognitive sequelae. The aim of this study was to evaluate the long-term outcomes and predictors of post-encephalitic sequelae in adult patients with TBE in Latvia. Methods: A retrospective cohort with prospective follow-up was used that included 105 adult patients hospitalized with laboratory-confirmed TBE between 2018 and 2024. The patients’ clinical and demographic data were extracted from medical records, and reassessments were performed ≥6 months after discharge using structured clinical and neurological evaluations for neurocognitive, subjective, and neurological sequelae. Disease severity was classified using the Mickienė and Bogovič criteria, and sequelae severity was defined according to the Bohr criteria for post-encephalitic syndrome (PES). Results: Sequelae were observed in 52/105 (49.5%) patients and were more frequent in meningoencephalitis than in meningitis cases (18/25 [72.0%] vs. 33/77 [42.9%]). The most common persistent symptoms were impaired concentration (33/52 [63.5%]), fatigue (29/52 [55.8%]), and sleep disturbances (21/52 [40.4%]). Neurological sequelae included tremor (23/52 [44.2%]), vertigo (11/52 [21.2%]), and hearing impairment (5/52 [9.8%]). According to the Bohr criteria, most of the patients had mild sequelae (42/52 [80.8%]), while 10/52 [19.2%] had moderate sequelae; no severe cases were observed. In the multivariable analysis, increasing age was independently associated with greater sequelae severity (OR = 1.045 per year; 95% CI, 1.015–1.073; p = 0.003). Sex, comorbidities, biphasic disease, and length of hospital stay were not significant predictors. Acute neurological manifestations, particularly paresis (p = 0.002) and tremor (p = 0.019), were associated with worse outcomes. Although the disease severity scores correlated with sequelae in unadjusted analyses, neither the Mickienė nor the Bogovič classification independently predicted outcomes after adjustment. Conclusions: Nearly half of the hospitalized patients with TBE included in this study developed long-term sequelae, which were predominantly neurocognitive and mild in severity. Age was the primary independent predictor of worse outcomes, while acute neurological deficits such as paresis and tremor also indicated increased risk. These findings highlight the substantial burden of post-encephalitic syndrome and the need for structured long-term follow-up in TBE survivors.