Australian influenza report 2013—31 August to 13 September 2013 (#07/2013)

The Australian Influenza Report is compiled from a number of data sources, including laboratory-confirmed notifications to NNDSS, sentinel influenza-like illness reporting from General Practitioners and Emergency Departments, workplace absenteeism, and laboratory testing. Reports are produced fortnightly from May to October. A more in-depth end-of-season report is also published in Communicable Diseases Intelligence.

Page last updated: 01 October 2013

Current Report Summary

  • Nationally the 2013 influenza season appears to have peaked. Overall influenza activity has been relatively low compared to 2011 and 2012.
  • Since the beginning of the year there have been 17,990 laboratory confirmed cases of influenza reported including 2,992 in the past fortnight. Consistent with reporting periods throughout the season, the majority of this period’s notifications were reported from NSW (1,387).
  • Nationally, whilst influenza A remains the predominant influenza virus type, the proportion of influenza B this season has been higher than in recent years. Influenza A(H1N1)pdm09 has also re-emerged this season with approximately 15% of overall notifications have been reported as influenza A(H1N1)pdm09 compared to <1% of notifications in 2012.
  • Across jurisdictions, the distribution of influenza types and subtypes is variable. In Western Australia, influenza A(H3N2) remains the predominant subtype, however the proportion of A(H1N1)pdm09 is increasing. Influenza type B continues to represent over half of Victoria's influenza notifications. In recent weeks there have been increasing proportions of influenza B in South Australia and Queensland.
  • Notification data show that there is a predominance of influenza B infections in those aged less than 15 years, with influenza A infections peaking in the 0-4 and 30-34 years age groups. Consistent with A(H1N1)pdm09 dominant years, there are very few notifications of this subtype in those aged 65 years and over.
  • The rate of influenza associated hospitalisations has been relatively stable since 16 August. Almost 15% of influenza cases have been admitted directly to ICU. The age distribution of hospital admissions shows peaks in the 0-9 and over 60 years age groups.
  • Interim vaccine effectiveness estimates suggest that immunisation with the seasonal influenza vaccine reduces a person’s risk of requiring medical treatment or hospitalisation with confirmed infection with any influenza virus by 40-64%. The 2013 trivalent influenza vaccine was estimated to be more effective against infection with influenza B viruses than influenza A viruses.
  • The WHO has reported that influenza activity in the northern hemisphere temperate zones remains at inter-seasonal levels. In the temperate countries of South America and Southern Africa, influenza transmission peaked in late June and was primarily associated with influenza A(H1N1)pdm09.

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