Despite encephalitis being associated with significant morbidity and mortality, the aetiology is unknown in the majority of patients. The authors describe a retrospective cohort of encephalitis cases in 19 hospitals from New Orleans, Louisiana and Houston, Texas between 2000–2017. 340 adults (aged ≥17 years) with confirmed encephalitis were enrolled, 57% of whom had unknown aetiologies. PCR of the CSF for herpes simplex virus (HSV) and varicella zoster virus was performed in 69% and in 24% of patients, respectively. In addition, arboviral serology was performed on 49% of patients and anti-N-methyl-D-aspartate receptor antibody levels measured in 14%. 53% of the patients experienced adverse clinical outcomes (ACO) upon discharge. Older patients (>65 years of age) had a lower prevalence of HIV, higher number of comorbidities, were less likely to receive adjuvant steroids, and were more likely to have a positive arbovirus serology, a positive HSV PCR, abnormal CT findings and to have ACO. Prognostic factors that were independently associated with an ACO were age ≥65 years, fever, Glasgow coma scale (GCS) <13 and seizures. Therefore encephalitis leads to adverse clinical outcomes and has an unknown aetiology in the majority of patients, despite molecular diagnostics.
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