Characteristics and outcomes of influenza-associated encephalopathy cases among children and adults in Japan, 2010-2015

Abstract

Background

Influenza-associated encephalopathy (IAE) can result in severe neurologic disease with high mortality. Most IAE cases have been reported among children worldwide; understanding of IAE among adults is limited.

Methods

Data were collected on IAE cases reported through the National Epidemiological Surveillance of Infectious Diseases database in Japan during 2010 through 2015. IAE cases were stratified by age category and analyzed using descriptive statistics to assess differences in characteristics and outcomes.

Results

Among 385 reported IAE cases, median age at diagnosis was 7 years (range 0-90), and 283 (74%) were children aged <18 years. The mean seasonal incidence of IAE cases among children and adults (≥18 years) was 2.83 and 0.19 cases per 1,000,000 population, respectively. IAE incidence did not vary by predominant influenza A virus subtype. The frequency of IAE was highest in school-aged (5-12 years) children (38%), followed by young children aged 2-4 years (21%) and adults aged 18-49 years (11%). The proportion of cases with seizures was more common in pediatric IAE cases. There were more cases with cerebrospinal fluid pleocytosis among adults than in children (p<0.01), especially among those aged 18-49 (17%) and 50-64 (19%) years. Case fatality proportion was highest in those aged 40-64 (17%) and ≥65 (20%) years.

Conclusions

We identified differences in the characteristics of IAE patients between adults and children in Japan. Although IAE cases were more frequently reported among children, mortality was higher in adults. Further efforts are needed to prevent and improve survival of patients with IAE, especially in adults.