Prognosis

Eastern equine encephalitis virus infection is the most deadly encephalitic arbovirus infection in North America. The case fatality rate is approximately 30%.[1][9]​[33]​​​

In the absence of neurological symptoms, febrile illness usually resolves in 1 to 2 weeks.[4] If neurological symptoms are present, they tend to appear several days into the course of illness. Severe cases result in coma and death, which usually occurs 2 to 10 days after symptom onset, but can occur later. Of those who recover, approximately 50% have neurological sequelae.[1][33]

Prognosis may be better in patients over age 40 years, and in patients who experience a longer prodrome (e.g., >3 days).[33][62]​ The size of radiographic lesions in the brain does not appear to be associated with outcome; however, pleocytosis in cerebrospinal fluid and severe hyponatraemia have been correlated with poor outcomes.[46]

Long-term sequelae

Approximately half of the patients who recover are left with neurological or physical sequelae.[1][33]​ Neurological sequelae may be long-term, consisting of gross and fine motor impairment, cranial nerve dysfunction, mild brain dysfunction, memory impairment, behavioural changes, personality disorders, weakness, paralysis, seizures, tremors, or severe intellectual impairment.[1][11][63]

Immunity

Infection is thought to provide lifelong immunity against reinfection. However, it is important to note that immunity does not protect against other alphaviruses.[8]

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