Higher than expected seasonal influenza activity in Victoria, 2007

In 2007, the Victorian influenza season exceeded normal seasonal activity thresholds. The average rate of influenza-like illness (ILI) reported by general practitioners (GPs) participating in sentinel surveillance was 9.0 cases per 1,000 consultations, peaking at 22 cases per 1,000 consultations in mid-August. The average ILI rate reported by the Melbourne Medical Locum Service (MMLS) was 11.5 per 1,000 consultations over the season. The MMLS ILI rate peaked at 30 per 1,000 consultations at the same time as peak rates were reported by GPs, with a secondary peak observed three weeks later (22 cases per 1,000 consultations). Influenza cases notified to the Victorian Department of Human Services peaked in mid-August with a secondary peak of influenza A in early September. Of the influenza positive swabs collected by GPs and among those collected throughout the state, 92% were type A and 8% were type B. The most common strains identified in Victoria in the 2007 influenza season were A/ Brisbane/10/2007-like followed by A/Solomon Islands/3/2006-like. While neither virus strain was specifically included in the 2007 Australian influenza vaccine, reasonable cross protection was afforded by the strains in the vaccine.