[Epidemiology--surveillance information].

Recent data of the National Epidemiological Surveillance of Infectious Diseases (NESID) showed that neurological complications associated with influenza virus infection, such as acute encephalitis/encephalopathy (excluding Reye's syndrome) have increased in number especially among young children. Further investigation is necessary to find the pathogenesis of these serious complications and clarify whether this phenomenon is due to unclarified factor(s) unique in Japan or it has reminded unrecognized in other countries.