Influenza surveillance in the Pacific Northwest 1976-1980

Between June 1976 and June 1980 active year-round surveillance for influenza was carried out in Seattle in order to establish an early warning system. This report compares yield by different community groups and age. Waves of influenza virus infection appearing in three successive springs were followed in each instance by epidemics with the same subtype virus(es) in the following winter. These included two co-circulating A/H3N2 variants (A/Victoria/75 and A/Texas/77) in spring 1977 and winter 1977-1978, A/H1N1 (A/USSR) in spring 1978 and H1N1 (A/Brazil) winter 1978-1979, and type B influenza in spring 1979 and winter 1979-1980. Despite intensive surveillance through the summer and fall, the first isolate was not obtained until early December each year. Young adults (18-30) were as good sources for influenza viruses as children (less than 18).