1120. National Surveillance of Influenza A(H1N1)2009-Associated Encephalopathy Japan, 2009-2010
Session: Poster Abstract Session: Influenza and H1N1 Diagnosis, Epidemiology, and Viral Outcome
Saturday, October 22, 2011
Room: Poster Hall B1
  • 111022 IAE IDSA poster3.pdf (179.9 kB)
  • Background: Influenza associated encephalopathy (IAE) is known as a rare but serious complication of influenza. IAE cases have been reported from Japan and other countries, although its pathogenesis is still unclear. IAE has been a notifiable disease as a part of acute encephalitis/encephalopathy surveillance system in Japan since 2004. Many IAE cases were reported during influenza A(H1N1)2009 pandemic. The main objective of this study is to describe epidemiological features of pandemic IAE.

    Methods: The first pandemic wave in Japan started in July, 2009 and waned in March, 2010, according to sentinel influenza surveillance. We described epidemiological features of the reported IAE cases from week 28 in 2009 to week 27 in 2010, and compared them with those of seasonal IAE in previous five seasons. We used the case definition of acute encephalitis/encephalopathy surveillance under Infectious Disease Control Law in Japan.

    Results: While the number of reported IAE cases during five seasons before pandemic was 246, 331 IAE cases were reported during the first pandemic wave. According to laboratory results, 322 of them were considered to be influenza A(H1N1)2009 associated encephalopathy. The median age of pandemic IAE and seasonal IAE was seven years (range, 0-72) and four years (range, 0-83) respectively (p<0.0001, Mann-Whitney U test). Male patients account for 61% in pandemic, and 52% for seasonal influenza (p=0.047, chi-square test). The case fatality rate (CFR) of pandemic IAE was 3.7%, which was significantly lower than that of seasonal IAE (13.2%, p<0.0001, chi-square test). Although the greatest number of pandemic IAE cases was observed in 5-9 years of age, the number of cases per estimated number of ILI visit was peaked in 0-4 years of age.

    Conclusion: A number of IAE cases were reported in Japan during the first pandemic wave. Age and sex distributions were different from those of seasonal IAE. The CFR of pandemic IAE was lower than that of seasonal IAE. Surveillance of IAE in other countries would be helpful to understand this severe complication of influenza and a better epidemiological case definition is needed for data integration and comparison.

    Subject Category: V. Virology including clinical and basic studies of viral infections, including hepatitis

    Yoshiaki Gu, MD, MPH1,2, Tomoe Shimada, MD, MPH2, Yoshinori Yasui, MD, PhD2, Yuki Tada, MD, PhD2, Mitsuo Kaku, MD, PhD3 and Nobuhiko Okabe, MD, PhD2, (1)Department of Regional Cooperation for Infectious Diseases, Tohoku University Graduate School of Medicine, Sendai, Japan, (2)Infectious Disease Surveillance Center, National Institute of Infectious Diseases, Japan, Tokyo, Japan, (3)Department of Infection Control and Laboratory Diagnostics, Tohoku University Graduate School of Medicine, Sendai, Japan


    Y. Gu, None

    T. Shimada, None

    Y. Yasui, None

    Y. Tada, None

    M. Kaku, None

    N. Okabe, None

    Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.