Acute encephalitis from 1967 to 1991

We studied all the adult patients with acute encephalitis, 322 in all, in t he Helsinki area, Finland, during the years 1967-1991. The average incidenc e was 1.4/100 000 adults/year. The proportion of known and suggested etiolo gies in 5-year periods has risen from 36 (1967-71) to 59% (1987-91). Herpes simplex virus was identified most often (16%), followed by varicella-zoste r (5%), mumps (4%), and influenza A viruses (4%), In addition, 20 other age nts were identified. The leading cause of encephalitis in patients aged 65 years or more was varicella-zoster virus. Eighteen patients (5.6%) died. It appears that the etiology of encephalitis changes with age and with time. It is important to establish the etiological pattern, as this assists in pr ompt diagnosis, which is a prerequisite for successful therapy. (C) 2001 El sevier Science B.V. All rights reserved.