摘要：Epidemiological and virological studies were carried out on type A (H3) influenza viruses isolated in Osaka City during the past 4 seasons from 1997/1998 to 2000/2001. In the 1997/1998 season, incidence of clinically diagnosed influenza patients were reported to be about 8, 800 by a sentinel clinic made up of pediatricians (and partly of general physicians), and all 114 strains isolated were type A (H3) viruses. Schoolchildren were the main targets of the influenza epidemics. Thirty five percent of the patients were infected with type A (H3) viruses and showed temperatures higher than 40°C; as opposed to 20% infected with type A (H1) viruses and 22% with type B viruses who displayed temperarures over 40°C. The type A (H3) viruses caused acute encephalitis or encephalopathy in 10 children during the influenza epidemic seasons, of which 2 resulted in death. Two influenza virus strains [(A/Osaka City(OC)/02/01(H3)] and A/OC/05/01(H3) isolated in the 2000/2001 season showed titers of less than 4 against the 1G9 monoclonal antibody in both hemagglutination inhibition and neutralization tests, whereas the remaining 5 strains in the same season showed titers higher than 64 in the tests. Thus it was shown that 2 variants of the type A (H3) were prevalent in one season in a narrow area of Osaka City.
