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Observational Study
. 2019 Aug;24(33):1900421.
doi: 10.2807/1560-7917.ES.2019.24.33.1900421.

Intense interseasonal influenza outbreaks, Australia, 2018/19

Ian G Barr  1   2 , Yi Mo Deng  1 , Miguel L Grau  3 , Alvin X Han  4   5 , Robin Gilmour  6 , Melissa Irwin  7 , Peter Markey  8 , Kevin Freeman  9 , Geoff Higgins  10 , Mark Turra  10 , Naomi Komadina  1 , Heidi Peck  1 , Robert Booy  11   12 , Sebastian Maurer-Stroh  13   4   5 , Vijaykrishna Dhanasekaran  1   3 , Sheena Sullivan  1   2
Affiliations
Observational Study

Intense interseasonal influenza outbreaks, Australia, 2018/19

Ian G Barr et al. Euro Surveill. 2019 Aug.

Erratum in

  • Authors' correction for Euro Surveill. 2019;24(33).
    Eurosurveillance editorial team. Eurosurveillance editorial team. Euro Surveill. 2019 Aug;24(34):1908221. doi: 10.2807/1560-7917.ES.2019.24.34.1908221. Euro Surveill. 2019. PMID: 31456561 Free PMC article. No abstract available.

Abstract

BackgroundInterseasonal influenza outbreaks are not unusual in countries with temperate climates and well-defined influenza seasons. Usually, these are small and diminish before the main influenza season begins. However, the 2018/19 summer-autumn interseasonal influenza period in Australia saw unprecedented large and widespread influenza outbreaks.AimOur objective was to determine the extent of the intense 2018/19 interseasonal influenza outbreaks in Australia epidemiologically and examine the genetic, antigenic and structural properties of the viruses responsible for these outbreaks.MethodsThis observational study combined the epidemiological and virological surveillance data obtained from the Australian Government Department of Health, the New South Wales Ministry of Health, sentinel outpatient surveillance, public health laboratories and data generated by the World Health Organization Collaborating Centre for Reference and Research on Influenza in Melbourne and the Singapore Agency for Science, Technology and Research.ResultsThere was a record number of laboratory-confirmed influenza cases during the interseasonal period November 2018 to May 2019 (n= 85,286; 5 times the previous 3-year average) and also more institutional outbreaks, hospitalisations and deaths, than what is normally seen.ConclusionsThe unusually large interseasonal influenza outbreaks in 2018/19 followed a mild 2018 influenza season and resulted in a very early start to the 2019 influenza season across Australia. The reasons for this unusual event have yet to be fully elucidated but are likely to be a complex mix of climatic, virological and host immunity-related factors. These outbreaks reinforce the need for year-round surveillance of influenza, even in temperate climates with strong seasonality patterns.

Keywords: Australia; human; influenza; seasonality.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

Figure 1
Figure 1
Climatic map of Australia, 2018
Figure 2
Figure 2
Selected influenza surveillance data, Australia, 2014–2019
Figure 3
Figure 3
Virological influenza data for the interseasonal period, Australia, November 2018–May 2019 (n = 2,965)
Figure 4
Figure 4
Evolutionary relationships of the haemagglutinin genes (maximum likelihood) of influenza A(H1N1)pdm09 (n = 835) and A(H3N2) viruses (n = 954), Australian haemagglutinin sequences shown from 2018/19 (n = 422 H1; n = 544 H3)
Figure 5
Figure 5
Structural images of influenza A(H1N1)pdm09 and A(H3N2) haemagglutinin molecules showing changes in the most commonly circulating clades in Australia, 2018/19
See this image and copyright information in PMC

References

    1. Australian Government Department of Health. Australian influenza surveillance report. No. 11, 8 to 21 October 2018. Canberra: Department of Health; 2018. Available from: https://www1.health.gov.au/internet/main/publishing.nsf/Content/95C0B11D...
    1. Australian Government Department of Health. 2017 influenza season in Australia: a summary from the National Influenza Surveillance Committee. Canberra: Department of Health; 2017. Available from: https://www1.health.gov.au/internet/main/publishing.nsf/Content/097F15A9...
    1. Australian Government Department of Health. National Notifiable Diseases Surveillance System. Canberra: Department of Health; 2019. Available from: http://www9.health.gov.au/cda/source/cda-index.cfm
    1. Australian Government Department of Health. Australian Influenza Surveillance Report. No. 3, 20 May to 2 June 2019. Canberra: Department of Health; 2019. Available from: https://www1.health.gov.au/internet/main/publishing.nsf/Content/4D293F7E...
    1. NSW Influenza surveillance reports for 2019. Sydney: NSW Ministry of Health. [Accessed: 22 Jul 2019]. Available from: https://www.health.nsw.gov.au/Infectious/Influenza/Pages/reports.aspx

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