Australian influenza report 2013—14 September to 27 September 2013 (#08/2013)

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: 16 October 2013

Current Report Summary

  • Nationally the 2013 influenza season appears to have peaked at the end of August. In comparison to recent seasons, overall influenza activity has been relatively low and the 2013 season appears to have started later, with the duration of the season appearing to have occurred over a shorter period.
  • Since the beginning of the year there have been 21,319 laboratory confirmed cases of influenza reported. Over the past fortnight there have been 2,415 notifications, a 32% decrease compared to the previous fortnight. Consistent with reporting periods throughout the season, New South Wales continued to report the highest number of notifications. Influenza notifications continue to decrease across most jurisdictions, with activity currently plateauing in Queensland, South Australia and Western Australia.
  • Nationally, influenza A continues to be the predominant influenza virus type. Influenza A(H1N1)pdm09 has also re-emerged this season with over 15% of overall notifications being reported as influenza A(H1N1)pdm09 compared to <1% of notifications in 2012. Overall, the proportion of influenza B this season has been higher than in recent years.
  • 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 continues to increase. Whilst the proportion of influenza type B nationally has remained relatively stable, there have been increasing proportions of influenza B in New South Wales, South Australia and Queensland; combined with decreases in Victoria.
  • 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 started to decline over the past fortnight. During the season around 12% of influenza cases were admitted directly to ICU and a high proportion of cases had known medical co-morbidities reported. The age distribution of hospital admissions shows a peak in the 0-9 years age group, with increasing numbers of admissions occurring in older age groups.
  • 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, however since July there has been an increase in the proportion of influenza A(H3N2) and influenza type B viruses.

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