Influenza epidemiology in patients admitted to sentinel Australian hospitals in 2019: the Influenza Complications Alert Network (FluCAN)

Influenza is a common cause of acute respiratory infection, and is a major cause of morbidity and mortality. This report summarises the epidemiology of hospitalisations with laboratory-confirmed influenza during the 2019 influenza season. The Influenza Complications Alert Network (FluCAN) is a sentinel hospital-based surveillance program that operates at sites in all jurisdictions in Australia. Cases were defined as patients hospitalised at any of the 17 sentinel hospitals with influenza confirmed by nucleic acid detection. Data were also collected on a frequency matched control group of influenza-negative patients admitted with acute respiratory infection. During the period 1 April to 31 October 2019 (the 2019 influenza season), there were 4,154 patients admitted with confirmed influenza to one of 17 FluCAN sentinel hospitals. Of these, 44% were elderly (≥ 65 years), 21% were children (< 16 years), 7.7% were Aboriginal and Torres Strait Islander peoples, 1.7% were pregnant and 73% had chronic comorbidities. Most admissions were due to influenza A infection (85%). Estimated vaccine coverage was 75% in the elderly, 49% in non-elderly adults with medical comorbidities, and 27% in young children (< 5 years). The estimated vaccine effectiveness in the target adult population was 42% (95% confidence interval [95% CI]: 36%, 49%). There were a larger number of hospital admissions detected with confirmed influenza in this national observational surveillance system in 2019 than in 2018.