Australian Influenza Surveillance Report - week ending 15 September 2017 (#09/2017)

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Page last updated: 26 September 2017

The Australian Influenza Surveillance Report is published on a fortnightly basis during the influenza season, typically between May and October. Influenza activity updates will be published outside of the seasonal period.

Australian Influenza Surveillance Report No 09 - week ending 15 September 2017

Summary

  • Influenza activity at the national level decreased this reporting fortnight after reaching a peak in mid-August. Despite the national decline, high levels of activity continue to be reported across the country, with seasonal activity in some states and territories yet to have reached a peak.
  • The peak week of national influenza activity this season has been at comparable or higher levels than in recent years, with high activity persisting for a number of weeks.
  • Moderate to high levels of influenza activity in the community are likely to continue for the next few weeks.
  • There has been more than two and a half times the number of laboratory confirmed notifications of influenza reported to the National Notifiable Diseases Surveillance System (NNDSS) this year when compared with the same period last year. An earlier season onset and introduction of rapid testing have contributed, in part, to this increase. Administrative backlogs in data entry experienced in some jurisdictions are likely to alter the pattern of notifications once the backlog is resolved.
  • National indicators of influenza-like illness (ILI) declined in the last fortnight, further supporting that the season has peaked nationally. The proportion of patients presenting to sentinel general practitioners with ILI and testing positive for influenza remained stable this fortnight, indicating that influenza remains a significant cause of ILI in the community.
  • Influenza A(H3N2) is currently the predominant circulating influenza A virus nationally. Influenza B viruses also continue to circulate, with the proportion of total notifications attributed to influenza B increasing this reporting fortnight.
  • Notification rates this year to date have been highest in adults aged 80 years or older, with a secondary peak in young children, aged 5 to 9 years. This is consistent with previous seasons where influenza A(H3N2) and influenza B, respectively, have predominated.
  • Admissions to sentinel hospitals with confirmed influenza decreased this reporting fortnight, following a peak in week 33. High levels of admissions have persisted for the last 6 weeks, consistent with the higher than average influenza activity in the community.
  • Clinical severity for the season to date, as measured through the proportion of patients admitted directly to ICU, and deaths attributed to pneumonia or influenza, is low to moderate. The proportion of patients admitted directly to ICU has been lower than in recent years.
  • To date, based on antigenic characterisation of circulating influenza viruses, the seasonal influenza vaccines appear to be a moderate to good match for circulating virus strains, depending on the strain. Vaccine effectiveness estimates, which provide an indication of how well the vaccine provides protection against influenza, are only available towards the end of the influenza season.

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