[Differences in influenza epidemics in Osaka City--epidemiological surveillance of infectious disease].

Influenza viruses in outpatients with influenza symptoms in Osaka City were analyzed in an epidemiological surveillance of infectious disease between 1989 and 1993. During influenza epidemics a mixed prevalence of several types of influenza viruses existed. Three types of influenza viruses, AH1, AH3 and B, were isolated during the 1990/1991 season. Remarkably the three types of viruses were discovered in samplings collected on the same day and within a narrow area inside a radius of 800-1,000m from the surveyed hospitals. Different types of viruses were detected between brothers and among school children from same housing complexes. Influenza AH3 viruses detected in 1992/1993 season differed in antigenicity from those detected in the 1990/1991 and 1991/1992 seasons. Therefore it appears that mutation of the AH3 virus contributed to the large-scale influenza epidemic which occurred in the 1992/1993 season.

Agglutination of human O erythrocytes by influenza A(H1N1) viruses freshly isolated from patients.

The hemagglutinin titers of 10 influenza A (H1N1) viruses were examined using the erythrocytes of several species. Human O erythrocytes showed the highest agglutination titer to the viruses, whereas chicken erythrocytes showed a low titer. These findings were noted for at least 10 passages by serial dilutions of the viruses in Madin-Darby canine kidney (MDCK) cells. All influenza A(H1N1) viruses, plaque-cloned directly from throat-washing specimens of patients, also agglutinated human O but not chicken erythrocytes. The results of a hemadsorption test indicated that chicken erythrocytes possess less affinity to MDCK cells infected with the A/Osaka City/2/88(H1N1) stain than to those infected with the A/Yamagata/120/86(H1N1) strain which is used as an inactivated influenza vaccine in Japan. However, there were no significant differences between the A/Osaka City/2/88 and the A/Yamagata/120/86 strains in the hemagglutination inhibition test. Since human O erythrocytes have high agglutination activity to influenza A(H1N1) and also to A(H3N2) and B viruses in MDCK cells, these erythrocytes may be useful for the serological diagnosis of influenza.