Report of the National Influenza Surveillance Scheme, 2019

This report describes influenza surveillance activities in Australia in 2019. Data were extracted from several sources constituting the National Influenza Surveillance Scheme. The 2019 influenza season in Australia was characterised by high activity overall, with 2.8 times as many laboratory-confirmed influenza notifications as the five-year mean value. There were an unusually high number of notifications reported in the 2018-2019 interseasonal period; an earlier peak in influenza notifications; and prolonged activity after the peak of the season compared to previous years. There was considerable variation in the timing of peak influenza activity between states and territories; however, this was not unexpected given climatic differences. Notification rates were highest in the 0-4 and 5-9 year age groups, and about 2.1 times higher in these age groups than the overall notification rate. The age-specific notification rates of influenza A were higher than the corresponding rates of influenza B in all age groups in 2019; however, the age-specific notification rate of influenza B was considerably higher among those aged 0-15 years compared to other age groups. In 2019, of laboratory-confirmed influenza notifications, 76.6% were influenza A (71.6% influenza A(unsubtyped), 3.9% A(H3N2) and 1.1% A(H1N1)pdm09) and 23.2% were influenza B. Similar trends were observed across many sentinel surveillance systems for influenza, with each sentinel system showing increased activity during the interseasonal period and earlier peak activity in 2019. High notification rates were reflected in an increase in sentinel hospital admissions with confirmed influenza. The burden placed on hospitals due to people admitted with influenza was high; however, severity (measured through the proportion of patients admitted directly to intensive care units) was moderate. Influenza was recorded as the underlying cause of death for fewer than 1% of all deaths that occurred in 2019.