We included 83 patients (51 IC and 32 IS), mean age 62 years, presenting with meningoencephalitis (83%), encephalitis (11%) and myeloradiculitis (6%). Presenting symptoms included malaise (75%), fever (69%), altered mentation (66%), and myalgias (35%).   MRI imaging was abnormal in 74% (51/69), demonstrating T2 FLAIR hyperintensities in 45% (brainstem, thalamus, temporal lobes), leptomeningeal enhancement (12%) and acute strokes in (23%).

Clinical features and diagnoses were similar between the two groups except for myalgia (45% vs 19%) and thalamic MRI T2 FLAIR (13% vs 0%) abnormalities which were more common in IS. IS patients were more likely to be treated with intravenous immunoglobulin (59% vs 12% p=<0.01) or interferon therapy (44% vs 10%, p=0.0003) but had increased odds of 90-day mortality on univariate analysis (Odds ratio 2.18; 95% CI 1.06-4.49, p=0.035). Other factors negatively associated with 90-day mortality on univariate analysis were positive CSF WNV PCR, intensive care admission, GCS<8 and mechanical ventilation, while the presence of positive serum WNV IgM antibodies was protective.

Compared to IC, IS patients with NiWNV are at a greater mortality risk despite treatment.  Larger studies validating targetable predictors of outcomes are warranted.