La Crosse viral encephalitis is well described in children, but to date, there are only 2 adult cases described in the literature. Despite the fact that pediatric infection can be life threatening and typically presents as a febrile meningoencephalitis often complicated by seizures and mental status changes, little is known about the presentation and course of adult infection. We report the largest case series of adult La Crosse encephalitis.

Inpatient data were reviewed between 2001 and 2012 to identify adults (≥18 years of age) with possible La Crosse encephalitis. Subsequent review of serologic testing was followed by a comprehensive chart review.

Ten cases were identified, with ages ranging from 20 to 80 years. Fever, headache, and hyponatremia were seen in the majority, while mental status changes occurred in 5 patients and seizures in 2 patients. The mean length of stay was 8.4 days (± 8.4); 3 patients required intensive care unit admission, 2 of them were intubated, and 4 patients required discharge to a rehabilitation facility.

La Crosse Virus produces a clinically significant encephalitis in adults, and a high level of suspicion should be maintained, particularly in endemic areas. There were no deaths, but La Crosse encephalitis in adults remained a morbid illness often associated with mental status changes, prolonged length of stay or intensive care unit admission, and frequent need for postdischarge rehabilitation.