title: Encephalitis after influenza in Sweden 1987-1998: a rare complication of a common infection.
abstract: The aim of this study was to investigate the incidence of influenza-related encephalitis in Sweden during 11.5 years. Studies from Japan report an increased incidence of influenza-related encephalitis/encephalopathy. Few other studies are available. We conducted a retrospective register-based study on the Swedish National Inpatient Register, which covers all Swedish hospitals. In 1987-1998, a total number of 14,250 hospitalized individuals had an influenza diagnosis (population incidence: 137 per million person-years). In-hospital mortality was 4.1%. Using three different approaches, only 21 cases of influenza-related encephalitis were found, corresponding to a rate of 1.5 per 1,000 hospitalized persons with an influenza diagnosis (population incidence 0.21 per million person-years). We conclude that encephalitis following influenza occurs rarely, or is an infrequently recognized, diagnosed or reported complication. The cases we studied in detail have all recovered without sequels.
authors.affiliation: Infectious Diseases Unit, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden. anders.hjalmarsson@ki.se
authors.forename: Anders
authors.initials: A
authors.lastname: Hjalmarsson
authors.forename: Paul
authors.initials: P
authors.lastname: Blomqvist
authors.forename: Maria
authors.initials: M
authors.lastname: Brytting
authors.forename: Annika
authors.initials: A
authors.lastname: Linde
authors.forename: Birgit
authors.initials: B
authors.lastname: Sköldenberg
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D018792:Encephalitis, Viral / Q000453:epidemiology* / Q000209:etiology* / Q000401:mortality; D005260:Female; D006801:Humans; D015994:Incidence; D007251:Influenza, Human / Q000150:complications* / Q000453:epidemiology* / Q000401:mortality; D008297:Male; D008875:Middle Aged; D012042:Registries; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult