Occurence of influenza

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    Influenza is a potentially life-threatening virus that spreads quickly from person to person. It is a significant public health issue in this country, with 10–20 percent of New Zealanders infected every year. While influenza can occur all year round, incidence generally peaks in winter and spring in New Zealand. Some studies suggest this is because the virus can survive longer outside the body in periods of colder weather and low humidity (dry conditions).

    Influenza infections may decline as our climate changes. Warmer projected temperatures and higher humidity during winter and spring may contribute to reduced annual influenza rates. However, influenza infection is also affected by factors besides temperature and humidity.

    We classified occurrence of influenza as supporting information.

    Key findings

    From 2000 to 2016, average weekly general practitioner (GP) consultations for influenza-like illness were highest in winter (weeks 26–34), peaking at 75.4 consultations per 100,000 patient population in week 30.

    • From 2000 to 2016 an average of 776 hospitalisations a year were related to influenza. The maximum was in 2015 with 2,028 hospitalisations and the minimum was in 2000, with 199 hospitalisations.
    Figure 1
    Note: Weekly consultation rates are from the national sentinel general practice-based surveillance, which usually operates from May to September (weeks 18–39). See Institute of Environmental Science and Research (2016) for more information.
    Weeks are ordered according to calendar year. 
    Figure 2
    Note: Weekly consultation rates are from the national sentinel general practice-based surveillance, which usually operates from May to September (weeks 18–39). However, this was extended in the past due to pandemic influenza (eg in 2009–10). See Institute of Environmental Science and Research (2016) for more information.
    Weeks are ordered according to calendar year.

    Definition and methodology

    Influenza is a significant public health issue in this country, with 10–20 percent of New Zealanders infected every year (Ministry of Health, 2017).

    These data are reported in an annual surveillance report by the Institute of Environmental Science and Research (ESR). See the 2015 report for more information (ESR, 2016).

    Some of the peaks in the data relate to influenza pandemics – when a new strain of virus infects many people in a very short time (Ministry of Health, 2017). For example, the Ministry of Health stated that in 2009, 1,122 hospitalisations and 35 deaths were caused by the influenza A (H1N1) pandemic, commonly referred to as swine flu.

    Influenza infection rates may decline as our climate changes – the survival and transmission of the virus decreases in high humidity (Tompkins et al, 2012). Warmer-than-normal temperatures and higher-than-normal humidity in winter and spring may result in reduced annual influenza rates. This is reflected in the climate-change health risks for influenza modelled as part of ESR’s Health Analysis and Information for Action (HAIFA) project (ESR, 2014). However, influenza infections are influenced by many other factors, including vaccination coverage, immunity, and population susceptibility. Influenza infections can occur all year round.

    Data quality

    We classified Influenza as supporting information

    Relevance

       This supporting information is an indirect measure of the ‘Impacts on public health' topic.

    Accuracy

       The accuracy of the data source is of high quality.

     See Data quality information for more detail.

     

    References

    Institute of Environmental Science and Research, (ESR) (2014). Health Analysis and Information for Action (HAIFA). Retrieved from http://haifa.esr.cri.nz/.

    Institute of Environmental Science and Research, (ESR) (2016). Influenza surveillance in New Zealand 2015 (PDF, 2MB). Retrieved from https://surv.esr.cri.nz.

    Ministry of Health (2017). Influenza. Retrieved from http://www.health.govt.nz.

    Tompkins, D, Brock, A, Jones, G, McBride, G, Tait, A, Benschop, … Slaney, D (2012). Modelling the impacts of climate change on infectious diseases in New Zealand: Health analysis and information for action (HAIFA) (PDF, 6MB). Retrieved from http://haifa.esr.cri.nz.

    Archived pages

    See Influenza (archived October 2017).

    Updated 19 October 2017

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