Surveillance for the 2009 pandemic influenza A (H1N1) virus and seasonal influenza viruses - New Zealand, 2009.

The 2009 pandemic influenza A (H1N1) virus, which was first identified in the United States and Mexico, was imported into New Zealand by a high school group returning from Mexico in late April 2009. By June, sustained community transmission of the virus had been established in New Zealand. To track the incidence of influenza-like illness (ILI) and compare the number of viruses identified as 2009 pandemic influenza A (H1N1) with the number identified as seasonal influenza, New Zealand public health officials analyzed weekly data from the country's sentinel general practitioner (GP) surveillance system and nonsentinel laboratory surveillance network for the period extending from the week ending May 3 through the week ending August 2. This report describes the results of those analyses, which determined that the number of viruses identified as 2009 pandemic influenza A (H1N1) rapidly overtook the number identified as seasonal influenza, and the peak weekly consultation rate for ILI was three times the peak rate in New Zealand during the same period in 2008. These findings demonstrate the value of using integrated epidemiologic and virologic surveillance in New Zealand to monitor the scope of an influenza epidemic, identify circulating strains, assist public health control measures, and guide effective use of influenza vaccines and antivirals.