Intense interseasonal influenza outbreaks, Australia, 2018/19

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Intense interseasonal influenza outbreaks, Australia, 2018/19
Intense interseasonal influenza outbreaks, Australia, 2018/19
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Publication Date:
15 August 2019
Barr Ian G, Deng Yi Mo, Grau Miguel L, Han Alvin X, Gilmour Robin, Irwin Melissa, Markey Peter, Freeman Kevin, Higgins Geoff, Turra Mark, Komadina Naomi, Peck Heidi, Booy Robert, Maurer-Stroh Sebastian, Dhanasekaran Vijaykrishna, Sullivan Sheena. Intense interseasonal influenza outbreaks, Australia, 2018/19. Euro Surveill. 2019;24(33):pii=1900421.
Background: Interseasonal 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. Aim: Our 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. Methods: This 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. Results: There 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. Conclusions: The 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.
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Funding Info:
The Melbourne WHO Collaborating Centre for Reference and Research on Influenza is supported by the Australian Government Department of Health. Thank you to all the Australian laboratories that supplied the influenza samples/isolates used in this study. VD and MG are supported by contract HHSN272201400006C from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, US Department of Health and Human Services, United, States. We thank Rapid Surveillance, Centre for Epidemiology and Evidence, Ministry of Health for advice on the most appropriate NSW ED surveillance indicator and for preparation of the data. The authors acknowledge the influenza HA sequences generated by laboratories and listed on GISAID, for a full list of submitting laboratories and accession numbers see Supplementary Table 1.
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