Diagnostic value of RT-PCR for detection of tick-borne encephalitis virus RNA in cerebrospinal fluid

Tick-borne encephalitis (TBE) diagnosis is mainly based on serology, which however can be difficult to interpret in previously TBE-vaccinate patients and in immunosuppressed patients. The objectives of this study were to investigate if the detection of tick-borne encephalitis virus (TBEV) RNA in cerebrospinal fluid (CSF) can be used to diagnose TBE, and to assess the relation of TBEV RNA positivity to clinical characteristics and disease severity. A retrospective study was conducted in TBE patients from Region Stockholm and Uppsala, Sweden, 2015–2020. CSF-samples were analysed for TBEV RNA using RT-PCR. Data on clinical parameters, retrieved from medical records, were analysed based on TBEV RNA positivity in CSF. CSF from 36 TBE patients were analysed for the presence of TBEV RNA. TBEV RNA was detected in twenty of these patients (56%). Patients with detectable TBEV RNA in CSF had a more severe disease, with a higher rate of intensive care and assisted ventilation treatment. Overall, the mortality was 40% in patients with detectable TBEV RNA in CSF. In a subgroup of 8 patients with immunosuppressive treatment and detectable TBEV RNA in CSF, 7 (88%) had a fatal outcome. TBEV RT-PCR can be used as a complement for diagnostics in patients with underlying comorbidities involving the immune system or immunosuppressive treatment. The presence of TBEV RNA in CSF may correlate to severe infection and an increased risk of fatal outcome.