Clinical Features of Tick-Borne Encephalitis in Adults: 10-Year Stockholm Study

Overview

This retrospective study analyzed 703 adult tick-borne encephalitis (TBE) cases in Stockholm from 2006 to 2015, revealing that 11% experienced severe disease and 1.4% died. Older age, comorbidities, immunomodulatory therapy, and vaccination breakthrough infections were associated with increased severity and mortality.

Background

Tick-borne encephalitis (TBE) is a viral infection transmitted mainly by Ixodes ticks, causing central nervous system disease with a biphasic clinical course. Severity ranges from mild symptoms to severe encephalitis, often requiring hospitalization. Although effective vaccines exist, incidence is rising in Europe, including Sweden, where TBE poses a growing public health challenge. Understanding clinical characteristics and risk factors in high-endemic areas is essential for optimizing prevention and management.

Data Highlights

Key Findings

• Severe TBE was significantly associated with age ≥50 years, underlying comorbidities, and prior complete vaccination (breakthrough infections).
• Patients receiving immunomodulatory therapy had a markedly higher case fatality rate (15%) compared to the overall cohort (1.4%).
• Most patients were unvaccinated, highlighting gaps in preventive measures.
• More than 70% of patients followed for over 6 months reported persistent symptoms, indicating substantial long-term morbidity.
• Hospitalization was common (75%), reflecting the disease's clinical burden in this population.

Clinical Implications

Clinicians should recognize older adults, patients with comorbidities, and those on immunomodulatory therapy as high-risk groups for severe TBE and poor outcomes. Vaccination remains critical but may not fully prevent severe disease in these populations, underscoring the need for optimized preventive strategies. Long-term follow-up and rehabilitation should be standardized to address persistent symptoms and improve recovery.

Conclusion

This large Scandinavian cohort confirms that TBE severity and mortality are increased in older patients, those with comorbidities, immunomodulatory therapy, and vaccination breakthrough cases. Enhanced prevention and standardized post-acute care are essential to reduce disease burden.

References

1. Lindquist et al. 2021 -- Clinical Features of Tick-Borne Encephalitis in Adult Individuals: A Retrospective Analysis Over a Decade in Stockholm, Sweden