Australian Influenza Surveillance Report and Activity Updates

The Australian Influenza Surveillance Report and Activity Updates are compiled from a number of data sources, which are used to monitor influenza activity and severity in the community. These data sources include laboratory-confirmed notifications to NNDSS; influenza associated hospitalisations; sentinel influenza-like illness (ILI) reporting from general practitioners and emergency departments; ILI-related call centre calls and community level surveys; and sentinel laboratory testing results.

Nationally, influenza activity continued to decrease this fortnight with no regions reporting widespread activity.

As at 10 October 2014, there have been 62,918 cases of laboratory confirmed influenza reported, which is almost three times the notifications received for the same period in 2013.

Over the 2013-14 interseasonal period, higher than usual numbers of influenza notifications were reported from most jurisdictions. Rates of interseasonal influenza have been generally increasing since the 2009 influenza pandemic. Notification data trends for 2014, show a sharp increase in mid-July, a peak in mid-August followed by a rapid decline to interseasonal levels in early October. Overall influenza activity remained elevated for approximately 12 weeks. Nationally, the timing of the season peak was similar to 2013 and 2011.

Across jurisdictions, influenza activity peaked in mid to late August and was followed by rapid declines. However in South Australia (SA) and Victoria (Vic), there was sustained peak activity for up to five weeks. While the majority of notifications this year were from New South Wales (NSW) (31%) and Queensland (Qld)(27%), two of the most populous jurisdictions, notification rates were highest in SA.

Nationally influenza A was the predominant influenza virus type, however the distribution of influenza types and subtypes was variable between jurisdictions and changed as the season progressed. Influenza A(H1N1)pdm09 predominated across most jurisdictions throughout the season, however influenza A(H3N2) was predominant in New South Wales and the Australian Capital Territory*, with late season increases noted in Qld, Western Australia (WA), the Northern Territory (NT) and Tasmania (Tas). In recent weeks, the typical, late season increase in influenza B infections has also been noted.

Notification rates have had a bimodal age distribution trend, with rates highest in those aged less than 5 years and in those aged 80 years and over, with a smaller peak among those aged 30-44 years. This age distribution trend, especially in the younger to middle aged populations is consistent with previous years dominated by influenza A(H1N1)pdm09, whereas infections in older age groups is typical of influenza A(H3N2).

The rate of influenza associated hospitalisations has declined steadily over the past month. The overall rate of influenza cases admitted directly to ICU was 10% which was less than the rate from 2012 and 2013 (around 12%). The majority of influenza associated hospitalisations in 2014 were due to influenza A infections, with very few associated with influenza B infection. Three quarters of hospitalisations had known medical co-morbidities reported. In Australia it has been estimated that there have been over 8,500 adult influenza-associated hospitalisations since April 2014. The age distribution of hospital admissions shows a peak in the 0-4 year age group, with hospitalisations increasing with increasing age, especially among those aged 65 years and over.

The severity of the 2014 influenza season was moderate across most jurisdictions. However, more severe activity was noted in NSW, where influenza A(H3N2) circulated at higher levels and affected people in older age-groups, which has led to a substantial number of outbreaks in aged care facilities.

The WHO has reported that the southern hemisphere influenza season seems to be coming to an end, with areas of high activity persisting in Oceania. Elsewhere influenza activity remained low, except for some tropical countries in the Americas.

The Australian Influenza Vaccine Committee (AIVC) agreed to adopt the WHO recommendations for the composition of the 2015 southern hemisphere influenza season vaccine.

This will be the final Australian Influenza Surveillance Report for 2014, unless unusual activity becomes apparent over the summer months.

* These subtyped ACT influenza cases have been reported as A(H3). Based on nationally available subtyping and charaterisation data, these cases are assumed to be A(H3N2).

Annual Reports

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Should you encounter issues in accessing the information contained either on this webpage or within the downloadable full reports please email flu (flu@health.gov.au) or contact the Department of Health switchboard on 02 6289 1555 or 1800 020 103.