[Epidemiology of acute encephalitis or encephalopathy in Japan].

Epidemiological situation on acute encephalitis in Japan from 2004 to 2009 are described. Acute encephalopathy suspected infectious disease origin such as influenza encephalopathy are involved. Data are based on the National Epidemiological Surveillance of Infectious Diseases (NESID) under Infectious Disease Control Law. During these 6 years, 1467 cases are reported. More than 50% of them are less than 10 year old, and top age group is 1 yo and the second group is 0 yo. In 2004, acute encephalopathy outbreak(cause unknown although mushroom poisoning was suspected) occurred in northern part of Japan, and this event was detected under this reporting system. Major cause of acute encephalitis/encephalopathy are influenza virus infection (acute influenza encephalopathy: AIE) and many AIE cases were reported during influenza A/H1N1 2009 outbreak. Eight cases of measles encephalitis among adolescence and young adult age were reported in 2007, however, no report since 2008.