341. Characteristics, Risk Factors, and Outcomes of Encephalitis in Older Adults

Background Encephalitis is a serious medical condition with adverse clinical outcomes seen in 50% of individuals. Older adults have higher rates of adverse outcomes in community-acquired meningitis but studies in encephalitis are lacking. Methods A multicenter retrospective chart review of adults with encephalitis as defined by the international encephalitis consortium between 2000 and 2017 at 19 hospitals in New Orleans, Louisiana and Houston, Texas. Patients were classified as younger adults (<65 years) and older adults (≥ 65 years of age). Results A total of 340 adults were enrolled; 71 (21%) with possible and 268 (79%) with probable or confirmed encephalitis. An etiology was documented in 151 (44.5%) cases with the most common causes being arboviruses (17%); Herpes simplex virus(HSV)(16.5%), and anti-N-methyl-d-aspartate receptor antibody (13.4%). A total of 62 (18.3%) were older adults. Older adults were more likely than younger adults to have comorbidities, a vesicular or petechial rash, abnormalities on head computerized tomography scan, and to have a positive HSVpolymerase chain reaction (PCR) and a positive arboviral serology (P < 0.05). Older adults were also less likely to have human immunodeficiency virus (P = 0.004) and to receive adjunctive steroids (32.4% vs. 60.8%, P = 0.002). There were no significant differences between older and younger adults regarding symptoms, neurological examination findings, CSF profile, use of empiric antibiotic and antiviral therapy, and need for mechanical ventilation or intensive care unit admission (P > 0.2). Older adults were also more likely to have an adverse clinical outcome than younger adults (65% vs. 50.5%, P = 0.04). Conclusion Older adults with encephalitis more commonly have HSV and arboviruses and have higher rates of adverse clinical outcomes despite having similar clinical presentations. Disclosures All authors: No reported disclosures.