Between 1 June and 15 October, in both 2009 and 2010, we screened for patients admitted to ICU with confirmed influenza A. Influenza A was confirmed by reverse transcriptase polymerase chain reaction (RT-PCR), antigen detection, or serology. H1N1 2009 and seasonal subtypes, H1N1 and H3N2, were determined by RT-PCR or specific serology. The laboratories were accredited by the National Association of Testing Authorities in Australia or by International Accreditation New Zealand. Population data for Australia and New Zealand were obtained from Australian Bureau of Statistics [7] and Statistics New Zealand [8] for 2009 and 2010.