Sequelae of encephalitis; report of a study after the California epidemic.

In a study of almost 500 patients to determine residual effects, the sequelae of both St. Louis and Western equine encephalitis were more prominent in the younger age group. Infants under three months with Western equine encephalitis had the greatest central nervous system damage. Forty-four per cent of this entire group had sequelae. In patients between one and four years of age, the incidence of sequelae was less. The Western equine infection was associated with the more disabling residual damage. Postencephalitic convulsions were fairly common in the younger patients with Western equine disease, but not in the St. Louis group. After the age of five the sequelae rate dropped. In all age groups the Western equine residual changes were more severe than the damage of St. Louis infection. Some infants, children and adults showed remarkable improvement from sequelae even as much as two years after the abnormalities occurred. With the longer period of follow-up, some late sequelae were noted in children and adults, primarily among those who had Western equine infection.