As part of the national program of virological influenza surveillance, influenza activity was monitored in a city of North Italy during five epidemic seasons (1997-2002) via clinical samples obtained from patients presenting with influenza-like illness (ILI). The aim was to detect early activity and identify influenza strains circulating in each epidemic season. The virological surveillance activity involved sentinel General Practitioners (GPs) identifying patients with ILL During the five seasons considered, annual influenza epidemics occurred in our city, with little differences in time and severity. Influenza A viruses isolated in this period were predominantly of the influenza A/H3N2 subtype, although in the 2000-2001 season influenza A/H1N1 was most prevalent. Sporadic cases of influenza A/H1N1 have also been reported during 1999-2000 influenza season, whilst influenza outbreak during the last season considered (2001-2002) was associated predominantly with influenza B. This study emphasizes the value of virological surveillance for the monitoring and prevention of influenza, providing isolates for further antigenic and genetic characterization and also for vaccine preparation.
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