Report of the National Influenza Surveillance Scheme, 2011 to 2018.

Abstract

This report describes influenza surveillance activities in Australia for the period 2011 to 2018. Data were extracted from several sources constituting the National Influenza Surveillance Scheme (NISS). Laboratory-confirmed influenza notification rates (per 100,000 population) increased from 122 in 2011 to 1,021 in 2017, before declining to 235 in 2018. The highest laboratory-confirmed notification rates during the eight-year period were from the smaller jurisdictions (South Australia and the Northern Territory), except in 2016 when Queensland reported the highest rate. Similar trends were observed in community reports of influenza-like illness (ILI), presentations of ILI to sentinel general practice (GP) sites, and influenza hospitalisations. Children aged 14 years or younger, and adults 65 years of age or older, had the highest notification rates of laboratory-confirmed influenza. Adults aged 65 years or older and patients with comorbidities had higher rates of influenza-associated hospitalisations and mortality. Over half of eligible patients admitted to sentinel hospitals (57%) received oseltamivir treatment, with 17% receiving the treatment within 48 hours of symptom onset. Influenza type A predominated over the eight years, except in 2015 when type B predominated. This trend was consistent with Australian World Health Organization Collaborating Centre (WHOCC) data for influenza isolates tested. Of influenza viruses circulating during the reporting period, A(H1N1) viruses were mostly antigenically similar to the vaccine strain A/California/7/2009 (H1N1), except in 2017 and 2018 when they were mostly similar to A/Michigan/45/2015. The A(H3N2) strains varied over the years but included the vaccine strains A/Perth/16/2009, A/Switzerland/9715293/2013, A/Hong Kong/4801/2014, and A/Singapore/INFIMH/2016. The B/Victoria/2/87 lineage (represented by the 2016 vaccine strain B/Brisbane/60/2008) and the B/Yamagata/16/88 lineage (represented by the southern hemisphere 2015 vaccine strain B/Phuket/3073/2013) were the circulating influenza B viruses during the reporting period. Influenza B accounted for just under a third of notifications (32%) from 2011 to 2018. Fifty-four per cent of influenza B viruses characterised by the Australian WHOCC site during the eight-year period were from the Yamagata lineage, although the proportion was higher (67%) when analysing the most recent four years (2015 to 2018). In contrast, during the 2010 season, 99% of all influenza B viruses characterised by the Australian WHOCC site were in the B-Victoria lineage. During the 2018 season the Australian WHOCC site detected, for the first time, swine A(H3N2)v virus from a human patient in Australia, highlighting the need to maintain vigilance for zoonotic infections.