Severe West Nile virus disease in healthy adults.

The inpatient records of 44 case patients with West Nile virus infection hospitalized in 2002 were reviewed. Sixty-five percent of the case patients had encephalitis, and 35% had aseptic meningitis. There was no significant difference in the distribution of aseptic meningitis versus encephalitis among adults aged < or =50 years compared with adults aged > or =65 years. Focal weakness, likely due to anterior horn cell involvement, was present in 10 case patients (overall rate, 23%; rate among patients with encephalitis, 34%). Case patients with focal weakness who were aged < or =50 years had monoparesis, whereas those aged > or =65 years had paraparesis or quadriparesis. The overall mortality rate was 14%, and the mortality rate in patients aged > or =65 years was 35%. Increased age was associated with an increased mortality rate. The presence of paraparesis or quadriparesis was not independently predictive of mortality.