Influenza surveillance system of Japan and acute encephalitis and encephalopathy in the influenza season

Abstract

It is clarified from the NESID that neurologic complications such as acute encephalitis/encephalopathy, apart from Reye's syndrome, have occurred associated with influenza virus infection, especially among young children. Further investigation should be necessary to find the pathogenesis of this serious complication of influenza virus infection and whether this is unique in Japan, due to unclarified factor/factors, or whether it has not been recognized in other countries.

Encephalitis after Influenza in Sweden 1987–1998: A Rare Complication of a Common Infection

“…We have no imminent explanation to our finding of the male predominance, though it was expected from the previously described case series [18,19,20,22,23,24,25,26]. Neither can we explain why few children were found, contrary to the increased incidence among children in Japan during the end of the study period [16, 17]. It is unclear whether this is due to surveillance bias, our study design, or a genetic predisposition among men.…”

“…There seem to be two different clinical types of influenza-related encephalitis, acute encephalitis which may progress to death, and postinfectious encephalitis, which occurs 2–3 weeks after recovery from influenza [8]. Comparing case series, young children more often have acute encephalitis/encephalopathy with a considerable mortality [16, 17], while adults more often contract a postinfectious encephalitis [18,19,20]. …”

“…Several studies from Japan reported an increased incidence of influenza-related encephalitis, particularly among children up to 6 years of age [16, 17, 21]. The national Japanese surveillance system of infectious diseases, started in 1981, reported 1–20 cases per year until 1997.…”

Technical Report: Reduction of the Influenza Burden in Children

“…Since 1994, more than 200 cases of severe, acute necrotizing encephalopathy associated with influenza infection in young children have been reported in Japan. [35][36][37] It typically manifests as sudden onset of high fever, severe convulsions, and rapid progression to coma. Radiographic imaging has revealed bilateral thalamic necrosis and brainstem involvement in some cases.…”

The Value of Standardized Case Definitions in Encephalitis Clinical Research

“…In addition, influenza has been increasingly recognized as a vaccine preventable cause of encephalitis, especially in children and adolescents. 67 Initial reports emerged from Japan and the United States [68][69][70][71][72][73][74][75] and recently, a number of case reports as well as surveillance reports by CDC have been issued on neurologic complications of Influenza A (in particular pandemic H1N1) disease. [76][77][78][79][80][81][82][83][84][85][86][87][88] Example 3: Encephalitis as an adverse event following immunization (AEFI)…”