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 personyears). 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.

Viral encephalitis associated with pandemic 2009 (H1N1) influenza A

“…In our cases no viral RNA was found in the CSF. This is in accordance with previous studies 1–8. Our patients were men, as are the majority of reported patients with neurological involvement during seasonal influenza 1–7.…”

“…This is in accordance with previous studies 1–8. Our patients were men, as are the majority of reported patients with neurological involvement during seasonal influenza 1–7. The clinical manifestations were similar to those described earlier in relation to seasonal influenza A or B, but more severe than on average, or the four cases with H1N1v reported in children 1–6.…”

“…The clinical manifestations were similar to those described earlier in relation to seasonal influenza A or B, but more severe than on average, or the four cases with H1N1v reported in children 1–6. Appearance of 2 cases of encephalitis among 82 cases of hospitalised patients with influenza in our centre was much more than would be expected from the rate of 0.5–1.5 encephalitis cases per 1000 hospitalised influenza positive persons reported from Sweden1 and is nearly as frequent as the reported 6 cases among 407 patients with influenza in Austria 2. Novel influenza A (H1N1) virus infection should be considered as an aetiological agent of viral encephalitis in adults also.…”

“…Encephalitis during influenza infection is a rare complication described mostly during epidemics 1 2. The majority of the reported cases have been in children, especially in Japan,3 but cases in older patients have also been described 4.…”

Equine influenza

“…Η παρου σία του ιού της γρίπης επιβεβαιώθηκε εργαστηριακά και στα δύο περιστατικά, ενώ δεν ανιχνεύθηκε ερπη-τοϊός, συνηγορώντας έτσι στο συμπέρασμα ότι ο ιός της γρίπης ενδέχεται να προκαλεί προσβολή του νευ ρικού συστήματος . Αντίστοιχος συσχετισμός του ιού της γρίπης με εγκεφαλίτιδα / εγκεφαλοπάθεια έχει περιγραφεί σε επιδημίες γρίπης στον άνθρωπο (Toovey, 2008, Hjalmarsson et al, 2009). …”