Australian influenza report 2009 - 4 - 10 July 2009 (#9/09)

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. It is produced weekly from May to October. A more in-depth end of season report is also published in Communicable Diseases Intelligence.

Page last updated: 10 July 2009

Report No. 9
Week ending 10 July 2009

A print friendly version of this report is available as a PDF (233 KB)

Key Points

Influenza in Australia

  • Influenza notifications have started earlier than in 2008, most likely due to increased testing of Influenza Like Illnesses (ILI) to detect pandemic (H1N1) 2009.
  • The number of confirmed pandemic (H1N1) 2009 influenza cases overtook the seasonal influenza cases from week 26 (20 June 2009), which could indicate that pandemic (H1N1) 2009 is replacing seasonal flu activity this winter.
  • The average proportion of positive influenza tests which were pandemic (H1N1) 2009 to the week ending 5 July 2009 was 76% nationally (85% WA, 59% NSW, 85% VIC), an increase from 70% the previous week. This is similar to what other Southern Hemisphere countries (i.e. New Zealand, Chile) are reporting.
  • Testing through the ASPREN sentinel GP network showed that 27% of respiratory tests conducted on ILI patients were positive for influenza. Of these, 88% were pandemic (H1N1) 2009 and 12% were influenza A unspecified.
  • ILI presentations in 2009 to the sentinel GP network have decreased slightly and are below levels seen at the same time in 2007 (the highest influenza season in recent years), but above levels seen in 2008, with 24 cases per 1,000 patients seen.
  • ILI presentations in 2009 to Emergency Departments in WA has increased in the week ending 5 July, but is lower than in 2007. The rate of ILI presentations to NSW Emergency Departments is 26.4 per 1000 presentations, the highest rate recorded since data became available.
  • Absenteeism rates for 2009 are marginally higher than those seen at the same time in 2007 and 2008 but are following a similar trend.
  • In the last week up to 9 July 2009 the Australian Paediatric Surveillance Unit (APSU) reported 14 notifications of children hospitalised with severe complications of influenza.
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    Pandemic (H1N1) 2009

  • As of 10 July 2009*, there were 7837 confirmed cases of pandemic (H1N1) 2009 in Australia, including 18 deaths. It should be noted that testing is focused on those moderate to severe cases, those who are vulnerable, and those in special populations.
  • The median age of confirmed pandemic (H1N1) 2009 is 19 years. This may rise as the focus changes to testing the severely affected or hospitalised individuals.
  • Males are overrepresented among pandemic (H1N1) 2009 notifications in the younger age groups, while the number of females is slightly higher from age 20 years. Males are also overrepresented in the deaths associated with pandemic (H1N1) 2009, with thirteen (72%) male deaths and five female deaths (28%).
  • Currently the percentage and rates of national notifications are as follows:

      % Notifications per 100,000
    ACT
    3.2%
    68.3
    NSW
    23.1%
    26.7
    NT
    6.4%
    207.7
    Qld
    23.9%
    43.6
    SA
    9.4%
    48.3
    Tas
    1.6%
    26.7
    Vic
    26.6%
    40.8
    WA
    5.0%
    18.1
    Australia
    100%
    37.3

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    However, these notifications also reflect the level of testing and do not accurately indicate the percentage of the population affected in each jurisdiction.
  • High rates in the NT reflect high rates in indigenous communities and testing practices in the NT.
  • Due to the presence of underlying chronic disease, some of which is undiagnosed, and their higher level of social disadvantage, Indigenous Australians are vulnerable to complications from the pandemic H1N1 2009 virus. Figures to date show that Indigenous Australians are approximately three times more likely than non-Indigenous Australians to be a confirmed case of pandemic (H1N1) 2009. While it is estimated that 2.4% of the Australian population is of Aboriginal and/or Torres Strait Islander origin, 7% of Australian confirmed cases are indigenous.
  • The daily number of confirmed cases of pandemic (H1N1) 2009 requiring hospitalisation continues to increase, from 3% before the PROTECT phase to 11% since PROTECT. This is an increase of 3% over the last week, reflecting the focus on testing only the more severe cases. In Week 28, an average of 30 hospitalised confirmed cases required intensive care on any given day.
  • Several jurisdictions have reported cases of pregnant women being admitted to hospital and ICU, reinforcing the fact that pregnancy, particularly in the second and third trimesters, is a risk factor for pandemic H1N1 2009 infection.
  • Three isolated cases of oseltamivir resistant viruses have been reported in Denmark, Japan and Hong Kong respectively. In Hong Kong, the resistant strain was identified in a case who had not been treated with antivirals. However, WHO considers that these were sporadic cases of resistance to oseltamivir and that there is no current evidence of widespread antiviral resistance.

    * At the time of issue of this report there were 10 453 confirmed cases of pandemic (H1N1) 2009 in Australia and 24 deaths.



    To date, 53 Australian influenza isolates have been tested for resistance/sensitivity to neuraminidase inhibitors. All have tested sensitive to oseltamivir and zanamivir.
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    Seasonal Influenza

    Seasonal influenza notifications have decreased in the last few weeks, reflecting the reduction in testing of ILI patients in the move to PROTECT. Notifications are considerably higher than for the same time in previous years, a result of increased testing for pandemic (H1N1) 2009.

    Currently the percentage and rates of national notifications are as follows:

      % Notifications per 100,000
    ACT
    2.2%
    54.4
    NSW
    14.6%
    17.6
    NT
    3.1%
    118.6
    Qld
    25.0%
    49.6
    SA
    9.7%
    50.5
    Tas
    1.7%
    28.0
    Vic
    39.1%
    62.3
    WA
    4.6%
    18.0
    Australia
    100%
    39.4


    Influenza A is the predominant seasonal influenza type reported by all jurisdictions. Very few cases of influenza B have been reported. Of the seasonal influenza A notifications, A/H3N2 is the predominant subtype reported by most jurisdictions.

    In 2009, rates of influenza are highest in people aged under 25 years. In previous seasons the highest rates of inflection were observed in children under 12 months and adults over 85 years old. This difference is likely to be a result of increased testing for pandemic (H1N1) 2009 across all age groups.

    To date, 66 Australian seasonal influenza isolates have been tested for resistance/sensitivity to neuraminidase inhibitors. 97% of A/H1N1 isolates, 0% of A/H3N2 isolates and 0% of Type B isolates have tested resistant to oseltamivir. None have tested resistant to zanamivir.
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    Influenza Activity in Australia

    Epidemiology of Influenza in Australia

    As Figure 1 shows, influenza activity in 2009 started earlier than in 2008 and there was a rapid increase in the number of confirmed influenza cases (both seasonal and pandemic (H1N1) 2009) from week 21. The high rates of seasonal influenza seen during May and June are most likely due to the increase in testing for pandemic (H1N1) 2009.

    On 17 June 2009, Australia commenced the transition to a new response phase called PROTECT, in which laboratory testing is directed towards people with moderate or severe illness; those more vulnerable to severe illness; and those in institutional settings. This will mean that the numbers of confirmed cases will not reflect how many people in the community have acquired pandemic (H1N1) 2009 infection but reflects numbers of confirmed cases among those most at risk. A decrease in daily notifications does not reflect a decrease in pandemic (H1N1) 2009 activity.

    The number of confirmed pandemic (H1N1) 2009 influenza cases overtook the seasonal influenza cases from week 26 (20 June 2009), which could indicate that pandemic (H1N1) 2009 is replacing seasonal flu activity this winter.

    Figure 1: Influenza activity in Australia, by reporting week, years 2008 and 2009*

    Influenza activity in Australia, by reporting week, years 2008 and 2009

    * Data on pandemic (H1N1) 2001 cases is extracted from NetEPI; data on seasonal influenza is extracted from the NNDSS.
    A small number of pandemic (H1N1) 2009 notifications from several jurisdictions were reported in NNDSS as Influenza A.
    Sources: NNDSS and NetEPI databases



    The age standardised rate of seasonal influenza notifications in 2009 as at 10 July 2009 is 38.6 per 100,000 population. This is similar to the age standardised rate of pandemic (H1N1) 2009 notifications (37.3 per 100,000 population) but is 3.4 times higher than the rate reported in 2008 for the same reporting period, which was 11.4 per 100,000 population. This difference is likely due to increased laboratory testing for all influenzas which has occurred during the current pandemic.
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    Figure 2 shows younger age groups as having the highest notification rates per 100,000 for both 2009 seasonal influenza and pandemic (H1N1) 2009. The difference in the pattern of age rates for the 2008 and 2009 seasonal influenza notifications has yet to be explained and may reflect testing protocols for seasonal influenza. The lower rate of pandemic (H1N1) 2009 notifications in older age groups might reflect previous exposure and the consequent development of antibodies (as reported in several studies1), or could also be an artefact of early testing in school outbreaks.

    Figure 2: Age distribution of standardised rates of influenza activity in Australia, years 2008 and 2009

    Age distribution of standardised rates of influenza activity in Australia, years 2008 and 2009

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    Proportion of pandemic (H1N1) 2009 to seasonal influenza

    The proportion of pandemic (H1N1) 2009 to seasonal influenza varies across jurisdictions. Most jurisdictions have reported that the proportion of pandemic (H1N1) 2009 has increased in recent weeks to be greater than that of seasonal Influenza A. Reports from the three National Influenza Centres (NICs) showed that the average proportion of confirmed influenza which was pandemic (H1N1) 2009 increased from 64% to 76% between 20 June 2009 and 5 July 2009. NICs in New South Wales (week ending 3 July) and Western Australia (week ending 5 July) reported increases in the proportion of influenza which was pandemic (H1N1) 2009 of 59% and 85% respectively. The Victorian laboratory reported a decrease in the proportion of pandemic (H1N1) 2009 among all influenzas. This proportion fell from 99% for the week ending 28 June 2009 to 85% for the week ending 5 July 2009. However, given the small numbers which may be tested in any given week, the change in proportion should be interpreted with caution.

    Over the last two weeks, for the days on which surveillance testing is conducted, ASPREN GPs reported 85 people presenting with ILI. Of these, 69% (59/85) were tested for influenza. Twenty-seven per cent (16/59) of these cases were influenza positive; 87.5% (14/16) were pandemic (H1N1) 2009 and 12.5% (2/16) were influenza A unspecified.
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    Sentinel Data

    Laboratory surveillance

    The Victorian Infectious Disease Reference Laboratory (VIDRL) reported that in the week ending 5 July 2009, Influenza A, picornavirus, and respiratory syncytial virus (RSV) were the most commonly detected respiratory viruses in Victoria (for full report see: www.vidrl.org.au). For the same period, South Australia reported that influenza A was the most commonly detected respiratory virus. New South Wales reported (week ending 3 July 2009) pandemic (H1N1) 2009 as the most commonly identified respiratory virus.

    In the week ending 3 July 2009, both the number of virology samples tested in New South Wales and the percentage of tests which were positive increased. The percentage of tests positive for influenza is approximately 40% and is much higher than at the same time in 2007 and 2008 (Figure 3). The expected decrease in testing as a result of the introduction of the PROTECT phase is not yet reflected in this graph.

    Figure 3. Number of all virology tests for respiratory Illness and percentage of tests positive for influenza, NSW, 2007 to 3 July 2009

    Number of all virology tests for respiratory Illness and percentage of tests positive for influenza, NSW, 2007 to 3 July 2009

    SOURCE: NSW HEALTH ‘NSW Influenza Surveillance Report’


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    Sentinel General Practice

    Data available from the Australian Sentinel Practices Research Network (ASPREN), the Northern Territory GP surveillance system, and VIDRL up until 5 July 2009 show that Influenza Like Illness (ILI) consultation rates have slightly decreased and are below levels seen in 2007 (Figure 4). In the last week, the presentation rate to sentinel GPs in Australia was approximately 24 cases per 1,000 patients seen.

    The first confirmed case of pandemic (H1N1) 2009 reported in Australia was on 9 May 2009 (week 20), corresponding with a subsequent increase in ILI consultations reported by sentinel GPs.

    As data from the Northern Territory and the VIDRL surveillance systems are being combined with ASPREN data, rates may not be directly comparable across 2007, 2008 and 2009.

    Figure 4. Rate of ILI reported from GP ILI surveillance systems from 2007 to 5 July 2009 by week*

    Rate of ILI reported from GP ILI surveillance systems from 2007 to 5 July 2009 by week

    * Delays in the reporting of data may cause data to change retrospectively.
    SOURCE: ASPREN, NT, VIDRL


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    Emergency departments

    The Western Australia Influenza Surveillance Program collects data from 8 Perth Emergency Departments (EDs). The number of ILI presentations reported in Western Australia EDs has increased in the week ending 5 July 2009, but is lower than in 2007 (Figure 5). The number of admissions through EDs of patients with ILI has slightly decreased from 33 to 31 admissions.

    Figure 5. Number of Emergency Department presentations due to ILI in Western Australia from 1 January 2007 to 5 July 2009 by week

    Number of Emergency Department presentations due to ILI in Western Australia from 1 January 2007 to 5 July 2009 by week

    In early July 2007 (week 26), several deaths associated with influenza infection were reported in children from Western Australia. The public response to these deaths could account for the sudden increase in ILI presentations to Perth EDs in 2007.
    SOURCE: WA ‘EDSS News’ Report


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    The New South Wales Influenza Surveillance Program collects data from 49 EDs across New South Wales. In the week ending 3 July 2009, ILI presentations to EDs increased significantly and are at the highest rate recorded since data became available (2002) (rate 26.4 per 1,000 presentations) (Figure 6). Presentations were mainly for mild illnesses, although 4% of presentations with ILI were admitted.

    Figure 6. Rate of ILI diagnosed in people presenting to selected Emergency Departments, NSW 1 January 2005 to 3 July 2009 by month*

    Rate of ILI diagnosed in people presenting to selected Emergency Departments, NSW 1 January 2005 to 3 July 2009 by month

    * Emergency department data are preliminary and may be updated in later weeks.
    SOURCE: NSW HEALTH ‘NSW Influenza Surveillance Report’


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    Paediatric hospital admissions

    The Australian Paediatric Surveillance Unit (APSU) conducts surveillance of severe complications of influenza in children aged 15 years and under. In 2009 surveillance began on 1 June, while in 2008 it commenced on 1 July. Details of admissions are reported on a weekly basis.

    In the last week up to 9 July 2009, the APSU reported 14 notifications of children hospitalised with severe complications of influenza. Of the 13 cases for which data are complete, seven cases are still hospitalised and two are in ICU. All cases were positive for influenza A and one of these cases was confirmed as positive for pandemic (H1N1) 2009. Complications were recorded in 12 of the 13 cases and 8 had underlying conditions.

    Since reporting began in 2009, 35 children have been reported as hospitalised with complications from influenza. Of the 24 cases for which data is available, the average age of children admitted to hospital is 2.5 years, with an age range from 1 month to 8 years.
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    Absenteeism

    A national organisation provides data on the number of employees who have been on sick leave for a continuous period of more than three days. These data are not influenza or ILI specific and absenteeism may be a result of other illnesses.

    Absenteeism rates continue to rise, possibly reflecting greater rates of illness in the community. Rates in 2009, are marginally higher and following similar trends to those seen in 2007 and 2008 (Figure 7).

    Figure 7. Absenteeism rates, 1 January 2007 to 24 June 2009, by week

    Absenteeism rates, 1 January 2007 to 24 June 2009, by week

    SOURCE: Absenteeism data


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    Pandemic (H1N1) 2009 Activity in Australia

    Epidemiology of H1N1 Influenza in Australia

    As of 10 July 2009 there were 7837 confirmed cases of pandemic (H1N1) 2009 in Australia, including 18 deaths (a Case Fatality Rate of 0.23). *

    * Please note that this figures differ from the one reported on the Situational Report released on 10 July 09 due to a lag in jurisdictional data entry.



    Distribution of cases over time

    The national epidemic curve shows the jurisdictional distribution of confirmed cases of pandemic (H1N1) 2009 over time in Australia (Figure 8). The epidemic curve shows several peaks, however the pattern is a surveillance artefact due to a change in testing policy. The vast majority of earlier confirmed cases occurred in Victoria, where case reporting peaked in late May before declining rapidly in early June due to a change to targeted laboratory testing implemented on 3 June 2009 as part of the modified SUSTAIN phase. The reported daily notification rate of confirmed cases in most other jurisdictions increased in the first half of June 2009 and has since declined as a result of targeted testing as part of the move to the PROTECT phase.

    Figure 8. Epidemic curve of confirmed cases of pandemic (H1N1) 2009 in Australia, by jurisdiction

    Epidemic curve of confirmed cases of pandemic (H1N1) 2009 in Australia, by jurisdiction

    Source: NetEPI database


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    Distribution of cases by age and sex

    The distribution of confirmed pandemic (H1N1) 2009 cases in Australia shows higher reporting rates in younger age groups, consistent with the age distribution of confirmed cases observed in other parts of the world.2 Of the 7737 confirmed Australian cases for whom age was known, the median age is 19 (same as in report period 27 June to 3 July). People aged less than 30 years accounted for 72% (5660) of all confirmed cases. The highest number of cases was in the 10–19 year age group (32% or 2517 cases), while children under five years accounted for 8% (624) of cases and people over 60 years accounted for 2.4% (185) of cases (Figure 9). The data need to be interpreted with caution, as case ascertainment could bias results. In the early weeks, active surveillance in schools may have skewed reporting, while the current focus on testing more severe cases or those with underlying illness may skew the age distribution towards an older age group.

    The gender distribution of cases in Figure 9 shows that males were over represented among confirmed cases in the younger age groups (from 0 to 19 years), while the number of females is slightly higher from age 20 years. Overall, the rate of confirmed cases of pandemic (H1N1) 2009 is slightly higher for males (37.8 per 100,000 population, compared to 36.1 for females).

    Figure 9. Laboratory confirmed cases of pandemic (H1N1) 2009 in Australia to 10 July 2009, by age group and sex

    Laboratory confirmed cases of pandemic (H1N1) 2009 in Australia to 10 July 2009, by age group and sex

    Source: NetEPI database



    The observation that there is more disease among younger age groups may indicate pre-existing immunity in older age groups from exposure to previously circulating H1N1 influenza viruses, or that there has been insufficient time for the virus to fully penetrate beyond the social networks of younger people initially infected. There may also have been bias in surveillance, for example through contact tracing of school contacts in the early stages of the pandemic in Australia.
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    Geographic distribution of cases

    Australia’s rate of pandemic (H1N1) 2009 notifications as at 10 July was 37.3 notifications per 100,000 population, an increase from 22.4 notifications per 100,000 population reported in the previous report.

    As at 10 July 2009, Victoria continued to have the greatest proportion (26.6%) of pandemic (H1N1) 2009 notifications reported in Australia, followed by Queensland (23.9%) and New South Wales (23.1%) (Table 1). Age standardised rates per capita vary across the jurisdictions, with the greatest rate per 100,000 population occurring in the Northern Territory (207.7 per 100,000), the Australian Capital Territory (68.3 per 100,000) and South Australia (48.3 per 100,000).

    The high rate of confirmed cases in the NT is primarily due to the high number of Indigenous cases when compared with other jurisdictions. Many of the confirmed Indigenous cases are from remote communities and have risk factors that make them vulnerable to infection. The higher rate may also reflect the increased laboratory testing of those who are most at risk under the PROTECT phase.

    Table 1. Notifications and age standardised rates of laboratory-confirmed pandemic (H1N1) 2009, by jurisdiction to 10 July 2009

    Jurisdiction Total H1N1 Influenza 09 notifications Percentage of pandemic (H1N1) 2009 notifications Age standardised rates per 100,000 Percentage of Australian population
    ACT
    248
    3.2%
    68.3
    1.6%
    NSW
    1814
    23.1%
    26.7
    32.6%
    NT
    499
    6.4%
    207.7
    1.0%
    QLD
    1875
    23.9%
    43.6
    20.0%
    SA
    733
    9.4%
    48.3
    7.5%
    TAS
    127
    1.6%
    26.7
    2.3%
    VIC
    2086
    26.6%
    40.8
    24.8%
    WA
    390
    5.0%
    18.1
    10.1%
    Australia
    7837*
    100%
    37.3
    100%

    * No jurisdiction identifier was available for 65 confirmed cases
    Source: NetEPI database


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    Aboriginal and Torres Strait Islander people/communities

    Due to the presence of underlying chronic disease, some of which is undiagnosed, and their higher level of social disadvantage, Indigenous Australians are vulnerable to complications from the pandemic H1N1 2009 virus.

    Figures to date show that Indigenous Australians are approximately three times more likely than non-Indigenous Australians to be or have been a confirmed case of pandemic (H1N1) 2009. As of the 10 July 2009, seven per cent (n=543) of confirmed cases are reported as Aboriginal and/or Torres Strait Islander* in the NetEpi database.**

    * It is estimated that 2.4 per cent of the total Australian population are Aboriginal and/or Torres Strait Islander.
    ** Note that in 15% of confirmed cases (1162/7837) reported in the NetEpi database the Indigenous field has not been completed.



    The median age of Aboriginal and/or Torres Strait Islander confirmed cases is 21 years of age (range 0-79 years of age) which is similar to the median age for all Australian confirmed cases (19 years). Sixty eight per cent (n=360) of confirmed cases are aged less than 30 years of age. As Figure 10) illustrates, age standardised rates for Indigenous peoples are higher across all age groups, when compared with non-Indigenous Australians. The discrepancy in rates is most marked in the 75+ year age group (26:1); the 55-59 year age group (13:1); and the 50-54 year age group (9:1).

    Fifty three per cent (n=287) are female and forty five per cent (n=246) are male. No data on gender is available for ten cases.

    Figure 10: Age standardised rates for confirmed cases of pandemic (H1N1) 2009 in Indigenous and non-Indigenous peoples in Australia, to 10 July 2009

    Age standardised rates for confirmed cases of pandemic (H1N1) 2009 in Indigenous and non-Indigenous peoples in Australia, to 10 July 2009

    Source: NetEpi database



    Sixty three per cent (n=343) of Aboriginal and/or Torres Strait Islander confirmed cases are in the Northern Territory, followed by 19% (n=104) in Queensland, 6% (n=35) in New South Wales, 5% (n=28) in Western Australia, 3% (n=18) in South Australia, 2% in the Australian Capital Territory (n=10), 1% in Victoria (n=3) and Tasmania has two cases.*3

    * New South Wales has the largest Indigenous population (30% or 152,685), followed by Queensland (28% or 144,885), Western Australia (14% or 70,966), Northern Territory (12% or 64,005), Victoria (7% or 33,517), South Australia (5% or 28,055), Tasmania (4% or 18,415) and the Australian Capital Territory has the smallest (0.8% or 4,282).



    An increasing number of Aboriginal and/or Torres Strait Islander communities in the Northern Territory are reporting outbreaks of pandemic (H1N1) 2009. Ten communities or towns are reporting ten or more confirmed cases, this compares with the last Australian Influenza Report where six communities reported outbreaks. Sixty eight confirmed cases have been reported in Aboriginal people in Alice Springs.

    Information on hospitalisation is available for 243 Aboriginal and/or Torres Strait Islander cases in the NetEpi database. Fifty nine of these cases are reported as having been hospitalised, with the majority of these (n=46) located in the Northern Territory. The states and territories are reporting that 101 (12%) of all 853 cases hospitalised since the beginning of the outbreak were Aboriginal and/or Torres Strait Islander.
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    Severe cases and hospitalisations of pandemic (H1N1) 2009, in Australia

    As of 10 July 2009, the jurisdictions have reported that 853 confirmed cases have been hospitalised, this will include people who are hospitalized for co-morbidities. The number of cases per day requiring hospitalisation has been increasing since mid June (Figure 11) and has increased by 80% in the last week (Week 28). This rise is to be expected with the increasing detection of pandemic (H1N1) 2009 in the community and may also reflect improved reporting of hospitalisation data by states and territories. Most hospitalised cases had underlying risk factors or co-morbidities, with the state of Victoria noting that 92% of their hospitalised cases had underlying risk factors. The proportion of cumulative cases requiring hospitalisation compared with the total number of confirmed cases increased from 3% on 15 June 2009 to 11% on 10 July 2009 (Figure 11). This reflects the change to the response phase PROTECT where laboratory testing is directed towards people with moderate or severe illness or those more vulnerable to severe illness who are more likely to require hospitalisation.

    For comparative purposes, for the period 2000-01 to 2006-07, an average of 1,925 people with influenza were admitted to hospital each year. For all influenzas and pneumonias, for the same period, an average of 73,271 people were admitted to hospital.4

    In Week 28, an average of 30 hospitalised cases required intensive care on any given day. This does not represent the number of new cases requiring admittance to an Intensive Care Unit (ICU) but is a repeated measure of the prevalence of confirmed cases in an ICU on a particular day. The length of stay in an ICU will differ depending on the severity of a particular case. Victoria has noted that the average length of stay in an ICU for a confirmed case is 8 days. In the last week, the average proportion of hospitalised cases in an ICU on any day was 28% (Figure12). This proportion is slightly lower than the previous week where 30% of cases were in an ICU. Most cases admitted to an ICU would be ventilated.

    Figure 11. Hospitalisations of pandemic (H1N1) 2009 and proportion of cumulative hospitalised cases compared with cumulative number of cases, 15 June 2009 to 10 July 2009, Australia

    Hospitalisations of pandemic (H1N1) 2009 and proportion of cumulative hospitalised cases compared with cumulative number of cases, 15 June 2009 to 10 July 2009, Australia

    * The jurisdictions report directly to the National Incident Room, Commonwealth Department of Health and Ageing, on hospitalisations and numbers admitted to ICUs.
    Source: Jurisdictions



    Figure 12. Proportion of hospitalised pandemic (H1N1) 2009 confirmed cases admitted to ICU compared with cases hospitalised,* 15 June 2009 to 10 July 2009, Australia

    Proportion of hospitalised pandemic (H1N1) 2009 confirmed cases admitted to ICU compared with cases hospitalised

    * The jurisdictions report directly to the National Incident Room, Commonwealth Department of Health and Ageing, on hospitalisations and numbers admitted to ICUs.
    From the beginning of the pandemic (H1N1) 2009 outbreak, 853 confirmed cases have been hospitalised. These numbers are small and the proportion reported as admitted to ICU should be interpreted with caution.
    Source: Jurisdictions



    Eighteen people in Australia* with confirmed pandemic (H1N1) 2009 infection died between 19 June 2009 and 10 July 2009. As a comparison, during the years 2001-2006 the average number of deaths from all influenzas for the month of June was 5 deaths and for July was 7 deaths. Deaths from all influenzas and pneumonias in June and July for the same period averaged 294 deaths and 347 deaths respectively. These account for 2-3% of all deaths in Australia during these months.5

    * For the most recent figures on hospitalisations and deaths please access the latest Situation Report at http://www.healthemergency.gov.au/internet/healthemergency/publishing.nsf/Content/updates



    The average age of confirmed cases that died was 47 years of age and the median age was 50 years (range 3-85 years of age). Most of the cases had underlying medical conditions; including cancer, diabetes mellitus and morbid obesity. Males are overrepresented in the deaths with thirteen (72%) of these cases male and five (28%) female.
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    Seasonal Influenza Activity in Australia

    Laboratory Confirmed Influenza

    There have been 8,283 cases of laboratory confirmed influenza diagnosed and reported to the National Notifiable Diseases Surveillance System (NNDSS) from 1 January 2009 to 10 July 2009 (Figure 13). There were 1,282 laboratory confirmed influenza cases in the same period last year
    (1 January 2008 to 10 July 2008).

    Influenza notifications are above the 5 year rolling mean for this period (Figure 14). The high notification rates are predominantly due to increased testing for influenza associated with the pandemic (H1N1) 2009 outbreak. Influenza notifications have decreased again in this reporting period (Figures 13 and 14). It is likely that this is related to the transition to the PROTECT phase as well as delays in reporting.

    Figure 13. Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 10 July 2009, by jurisdiction and week of diagnosis*

    Figure 13. Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 10 July 2009, by jurisdiction and week of diagnosis

    * NNDSS data excludes all the identifiable notifications of pandemic (H1N1) 2009. However, there are a small number of pandemic (H1N1) 2009 notifications reported in NNDSS as Influenza A, which will be correctly identified in future reports.
    SOURCE: NNDSS



    Notifications in 2009 have been predominantly from Victoria (39%), Queensland (25%), New South Wales (15%) and South Australia (10%). The Australian Capital Territory, the Northern Territory, Tasmania and Western Australia accounted for the other 12% (Table 2 and Figure 14).
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    The Northern Territory has reported the highest rate of seasonal influenza notifications per 100,000 population (119) followed by Victoria (62), the Australian Capital Territory (54), South Australia (51), and Queensland (50).

    Table 2. Number and rate of laboratory-confirmed notifications by jurisdiction, NNDSS, 1 January 2009 to 10 July 2009*

    State
    Cases Percentage of Total Notifications Crude rate per 100,000 Average Rate YTD 2004-2008 Percentage of Australian  population*
    ACT
    185
    2.2%
    54.4
    30.8
    1.6%
    NSW
    1210
    14.6%
    17.6
    22.0
    32.6%
    NT
    255
    3.1%
    118.6
    43.6
    1.0%
    Qld
    2074
    25.0%
    49.6
    39.4
    20.0%
    SA
    800
    9.7%
    50.5
    11.2
    7.5%
    Tas
    138
    1.7%
    28.0
    20.5
    2.3%
    Vic
    3242
    39.1%
    62.3
    14.1
    24.8%
    WA
    379
    4.6%
    18.0
    29.1
    10.1%
    Aus
    8283
    100%
    39.4
    4.8
    100%


    * NNDSS data excludes all the identifiable notifications of pandemic (H1N1) 2009. However, there are a small number of pandemic (H1N1) 2009 notifications reported in NNDSS as Influenza A, which will be correctly identified in future reports.
    SOURCE: NNDSS, ABS (2008 population)



    Figure 14. Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 10 July 2009, by jurisdiction and week of diagnosis*

    Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 10 July 2009, by jurisdiction and week of diagnosis

    * There are a small number of pandemic (H1N1) 2009 notifications reported in NNDSS as Influenza A. SOURCE: NNDSS


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    Subtyping information

    Of the 7,799 cases of influenza Type A notifications to NNDSS, 270 (3.5%) have been typed as A/H3N2, 148 (1.9%) have been typed as A/H1N1 and 7,381 (94.6%) as influenza A untyped. Influenza A untyped notifications in NNDSS may potentially be pandemic (H1N1) 2009. In some laboratories subtyping and pandemic (H1N1) 2009 testing is not carried out.
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    Age/ Sex Distribution

    National age-specific notification rates year to date show the highest rates of notifications continue to be in the 10–14 year age group (Figure 16). Rates of influenza across all ages are markedly different from those seen in 2008 when the highest rates were observed in children under 12 months and adults over 85 years. This year, rates of influenza are highest in those aged under 25 and this is likely to be a result of increase testing for pandemic (H1N1) 2009 across all age groups (Figure 15).

    Figure 15. Age standardised notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2009 to 10 July 2009, by age group and sex*

    Age standardised notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2009 to 10 July 2009, by age group and sex

    * NNDSS data excludes all the identifiable notifications of pandemic (H1N1) 2009. However, there are a small number of pandemic (H1N1) 2009 notifications reported in NNDSS as Influenza A, which will be correctly identified in future reports.
    SOURCE: NNDSS



    Mapping of influenza notifications by statistical division of residence indicates that there are areas within jurisdictions with higher rates compared to the rest of the jurisdiction or Australia (Figure 16). The numbers on the map indicate the number of cases occurring within each region. The rate of influenza is highest in the NT, likely due to cases of influenza occurring in areas where the population is quite small.

    Figure 16. Map of notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2008 to 9 July 2009, by Statistical Division of residence*

    Map of notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2008 to 9 July 2009, by Statistical Division of residence

    * NNDSS data excludes all the identifiable notifications of pandemic (H1N1) 2009. However, there are a small number of pandemic (H1N1) 2009 notifications reported in NNDSS as Influenza A, which will be correctly identified in future reports.
    SOURCE: NNDSS


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    Attachments

    International influenza surveillance

    As of 6 July 2009, the WHO has reported 94,512 cases of pandemic (H1N1) 2009 infection, including 429 deaths (a Case Fatality Rate of 0.45%).6 The WHO has since stopped reporting confirmed cases of pandemic (H1N1) 2009 infection.

    A number of countries with widespread transmission (the US, Mexico, Chile, Argentina, the UK) have moved towards a phase similar to the Australian phase PROTECT, where resources (including testing) are focused on providing the appropriate treatment for moderate to severe cases of pandemic (H1N1) 2009. These changes should be considered when looking at the following data.

    Countries in the Southern Hemisphere currently going through the winter influenza season have seen the highest increases in rates of pandemic (H1N1) 2009 notifications compared to the last reporting period.

    At 10 July 2009, the rate of pandemic (H1N1) 2009 notifications in Australia was 35.9 per 100,000 population. Chile continues to have the highest rate at 48.2 per 100,000 population, while Japan had the lowest at 1.2 per 100,000 population (Table 3).

    Table 3. Notification rates for pandemic (H1N1) 2009 in a selection of affected countries

    Country
    Crude rate per 100,000 population
    Southern Hemisphere
    Chile
    48.2
    Australia
    35.9
    New Zealand
    33.2
    Argentina
    6.2
    Northern Hemisphere
    Canada
    26.4
    UK
    12.1
    USA
    11.1
    Mexico
    9.4
    Japan
    1.2

    The above crude rates are calculated from the number of confirmed cases for each particular country as at 10 July 2009.



    New Zealand reported a sharp increase in ILI consultations through the sentinel surveillance in the week 6 to12 July (particularly in those aged under 19 years) with much higher consultation rates than previous years for the same week. About 74% of influenza viruses reported from sentinel surveillance and 54% of influenza viruses reported in non-sentinel surveillance were pandemic (H1N1) 2009. As of 12 July, New Zealand has reported a total of 1942 confirmed and probable cases of pandemic (H1N1) 2009, including 2 deaths and 345 hospitalisations. Of the 345 hospitalisations, pneumonia was recorded for 44 cases and acute respiratory distress syndrome was recorded of 6 cases. The highest notification and hospitalisation rates were seen in the under 1 year age group.7

    Chile has reported a similar situation up to 14 July, were pandemic (H1N1) 2009 represents 92% of the total circulating viruses in people over 5 years of age and 47% in those aged under 5 years. Of the pandemic (H1N1) 2009 confirmed cases as at 14 July (10,491), 62% are under 19 years of age, and 5.4% required hospitalisation. There has been 33 deaths associated with pandemic (H1N1) 2009.8

    Argentina has reported a total of 3,056 confirmed cases of pandemic (H1N1) 2009, including 137 deaths (mostly concentrated in the metropolitan region of Buenos Aires), becoming the second country with the highest number of reported deaths after the US (which reported 170 deaths).9
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    Antiviral Resistance Global update

    As per 10 July 2009, three cases of laboratory-confirmed oseltamivir resistance to the pandemic (H1N1) virus have been detected in Denmark, Japan and Hong Kong respectively. These viruses were found in three patients who did not have severe disease and all have recovered. The Hong Kong isolate was identified in a case who had not been treated with antivirals, meaning that she was infected with a resistant strain that was circulating in the community. It is likely that the case acquired the infection in the USA.10

    WHO considers that these were sporadic cases of resistance to oseltamivir and that there is no current evidence of widespread antiviral resistance. Based on this risk assessment, there are no changes in WHO’s clinical treatment guidance.11 A sample of Australian pandemic (H1N1) 2001 viruses is routinely tested for sensitivity to antivirals. All viruses tested to date continue to be sensitive to oseltamivir.
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    Data considerations

    The information in this report is reliant on the surveillance sources available to the Department of Health and Ageing. As access to sources increase and improve, this report will be refined and additional information will be included. This report aims to increase awareness of pandemic (H1N1) 2009 and seasonal influenza in Australia by providing an analysis of the various surveillance data sources throughout Australia. While every care has been taken in preparing this report, the Commonwealth does not accept liability for any injury or loss or damage arising from the use of, or reliance upon, the content of the report. Please note, the pandemic (H1N1) 2009 and seasonal influenza elements of this report are based on data available as at 10 July 2009. Delays in the reporting of data may cause data to change retrospectively. For further details about information contained in this report please contact the Influenza Team through flu@health.gov.au

    NetEpi

    All jurisdictions except QLD are reporting pandemic (H1N1) 2009 cases using NetEpi, a web-based outbreak case reporting system. Data from jurisdictional systems are being imported into NetEpi by VIC, NSW and WA, the remainder are entering directly into NetEpi. Qld ceased reporting into NetEpi on 6 July 2009.

    Analyses of Australian cases are based on clinical onset date, if this information is available. Where an onset date is not available, notification date has been used. Victorian cases use a calculated onset date which is the earliest available date calculated from specimen date, onset date, notification date or detection date. This assumption was made for all calculations and data on which the figures are based.

    State and Territory reporting

    The jurisdictions report directly to the National Incident Room, Commonwealth Department of Health and Ageing, on hospitalisations, numbers admitted to ICUs and deaths.

    National Notifiable Diseases Surveillance System (NNDSS)

    NNDSS comprises of notifications from jurisdictions of laboratory-confirmed influenza cases. Laboratory confirmed influenza is notifiable in all jurisdictions in Australia. Confirmed pandemic (H1N1) 2009 cases are being received from all jurisdictions through NNDSS except for Victoria and New South Wales. The Northern Territory and Tasmania are currently unable to distinguish between seasonal and pandemic (H1N1) 2009 cases and are reported as Influenza A.

    Laboratory Surveillance data

    Laboratory testing data are extracted from the ‘NSW Influenza Report,’ ‘The 2009 Victorian Influenza Vaccine Effectiveness Audit Report’ (VIDRL) and the ‘South Australian Seasonal Influenza Report’. These reports are provided weekly.

    WHO Collaborating Centre for Reference & Research on Influenza (WHO CC)

    Data are provided weekly to the Surveillance Branch from the WHO CC.

    Sentinel General Practice Surveillance

    The Australian Sentinel Practices Research Network (ASPREN) has Sentinel GPs who report influenza-like-illness (ILI) presentation rates in NSW, SA, ACT, VIC, QLD, TAS and WA. As jurisdictions joined ASPREN at different times and the number of GPs reporting has changed over time, the representativeness of ASPREN data in 2009 may be different from that of previous years. ASPREN data are sent to the Surveillance Branch on a weekly basis. Northern Territory GP surveillance data are sent to the Surveillance Branch on a weekly basis. VIDRL influenza surveillance data are sent to the Surveillance Branch on a weekly basis.
    A new testing protocol introduced through ASPREN requires GPs to test all patients presenting with an ILI on one day of the week. These data should provide a cross section of age, sex and severity of patients who seek GP assistance for ILI. This system is in the early stages of implementation and will be further developed over coming weeks.

    Sentinel Emergency Department (ED) data

    WA - ED surveillance data are extracted from the ‘EDSS News’ Report. This report is provided weekly.
    NSW - ED surveillance data are extracted from the ‘NSW Influenza Surveillance Report’. This report is provided weekly.

    Paediatric hospital admissions data

    Reports of ICU admissions are provided to the Surveillance Branch on a weekly basis by the Australian Paediatric Surveillance Unit.
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    References

    1. Kawaoka et al. In vitro and in vivo characterisation of new swine-origin H1N1 influenza viruses, published in Nature in July 2009: http://www.nature.com/nature/journal/vnfv/ncurrent/pdf/nature08260.pdf Accessed 15 July 2009.
    2. World Health Organisation: Weekly Epidemiological Record No. 25, 2009. Available at: http://www.who.int/wer/2009/en/; accessed 6 July 2009.
    3. Australian Bureau of Statistics, Experimental Estimates of Aboriginal and Torres Strait Islander Australians, June 2006. ABS cat. No. 3238.0.55.001, Canberra.
    4. Australian Institute of Health and Welfare (AIHW) National Hospital Morbidity Database. Available at: http://www.aihw.gov.au/hospitals/datacubes/index.cfm
    5. Australian Institute of Health and Welfare (AIHW). (2007) GRIM (General Record of Incidence of Mortality) Books. Retrospective mortality data: influenza and pneumonia. Available at: http://www.aihw.gov.au/mortality/data/grim_books_national.cfm
    6. World Health Organisation: Pandemic (H1N1) 2009 report update 58 (6 July 2009). Available at: http://www.who.int/csr/disease/swineflu/updates/en/index.html
    7. New Zealand Public Health Surveillance, Influenza Weekly Update. Available at: http://www.surv.esr.cri.nz/virology/influenza_weekly_update.php Accessed 16 July 2009.
    8. Chile Ministry of Health, Influenza A(H1N1) Weekly Report. Available at : http://www.redsalud.gov.cl/portal/url/page/minsalcl/g_varios/influenza.html Accessed 16 July 2009.
    9. Media report 14 July 2009. Available at: http://espanol.news.yahoo.com/s/reuters/090714/latinoamerica/latinoamerica_influenza_argentina_muertes
    10. Hong Kong Ministry of Health press release, 3 July 2009. Available from: http://www.dh.gov.hk/english/press/2009/090703-2.html Accessed 6 July 2009.
    11. WHO Pandemic (H1N1) 2009 briefing note: http://www.who.int/csr/disease/swineflu/notes/h1n1_antiviral_resistance_20090708/en/index.html Accessed 15 July 2009.