Australian influenza report 2009 - 27 June - 3 July 2009 (#8/09)

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: 03 July 2009

Report No. 8
Week ending 3 July 2009

A print friendly version of this report is available as a PDF (470 KB)

Key Points

The information in the influenza report is obtained from the national influenza surveillance system which is used to monitor seasonal influenza. This system collects data from many different sources. While it does contain some gaps, Australia’s influenza surveillance system is one of the most comprehensive among developed countries. A program to close the gaps and improve the system has been a long term project with still some years to go. While some modifications have been made to accommodate pandemic (H1N1) 2009 it is difficult to implement effective surveillance systems in a short time frame.

Influenza in Australia

  • Influenza notifications have started earlier that in 2008, most likely due to increased testing of ILI for Pandemic H1N1 influenza 09 and possibly because of the amount of Pandemic H1N1 influenza 09 in Australia.
  • The average proportion of positive influenza tests which were Pandemic H1N1 influenza 09 to the week ending June 28 was 70% nationally (75% WA, 71% NT, 51% NSW, 99% Vic), an increase from 64% the previous week.
  • ILI presentations in 2009 to the sentinel GP network is tracking similar to 2007, (the highest influenza season in recent years) with 25 cases per 1,000 patients seen.
  • ILI presentations in 2009 to Emergency Departments WA is similar to that seen in 2007 winter presentations. The rate of ILI presentations NSW EDs is much greater that in 2007 and 2008 but dropped in the last week reported.
  • Absenteeism for 2009 is tracking the same as the 2007 winter.
  • From 1 June to 3 July 2009 the Australian Paediatric Surveillance Unit (APSU) reported 21 notifications of children hospitalised with complications of influenza with data on 11. These have an average age of 2.7 years.

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    Pandemic H1N1 09

  • As expected in the PROTECT phase and as recommended by the WHO, the weekly number of cases confirmed with Pandemic H1N1 09 has fallen as testing focuses on those admitted to hospital, those in ICUs or those in special populations.
  • The median age of confirmed Pandemic H1N1 influenza 09 is 19 years and this may rise as the focus changes from testing around schools to testing of severely affected or hospitalised individuals.
  • Males and females appear similarly at risk of infection.

    Currently the percentage of national notifications are:
      % Notifications per 100,000
    Australia
    100
    22.4
    NT
    6.1
    134.4
    ACT
    3.9
    54.7
    Vic
    37.0
    33.5
    Tas
    2.0
    19.3
    Qld
    16.1
    18.2
    NSW
    24.1
    16.5
    WA
    6.2
    13.8
    SA
    3.6
    10.7


    However, these notifications also reflect the level of testing and do not accurately indicate the percentage of the population affected in each jurisdiction.
  • The daily number of cases of Pandemic H1N1 influenza 09 requiring hospitalisation continues to increase. The proportion of confirmed cases hospitalised was 3% before the PROTECT phase but has increased to 8% since PROTECT, reflecting the focus on testing only the more severe cases.
  • 21% of hospitalised cases have been admitted to an intensive care unit.
  • Several isolated cases of Tamiflu resistant viruses have been reported. In Hong Kong, the resistant strain was identified in a case who had not been treated with an antiviral. The WHO Collaborating Centre conducts resistance testing on Australian viruses. So far all have tested sensitive to oseltamivir. We will continue to monitor for evidence of oseltamivir resistance circulating in the community in Australia and overseas.
  • Indigenous cases are overrepresented in the number of confirmed cases of Pandemic H1N1 influenza 09, with 6% of cases compared to 2.4% of the population. Seventy five per cent of the indigenous cases were in the Northern Territory. Twelve per cent of Indigenous cases have been hospitalised compared to 8% in the total population.
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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 influenza 09

    Currently the percentage of national notifications are:
      % Notifications per 100,000
    Australia
    100
    22.4
    NT
    5.4
    182.3
    Vic
    40.2
    56.6
    SA
    9.9
    45.8
    ACT
    1.9
    41.8
    Qld
    23.5
    41.2
    WA
    4.5
    15.6
    NSW
    13.6
    14.5
    Tas
    0.9
    13.4


    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 55 years old. This difference is likely to be a result of increased testing for Pandemic H1N1 2009 across all age groups.

    The Northern Hemisphere 2008-09 influenza season saw a large rise in oseltamivir resistance in A/H1N1 viruses, up to 96% from 15% in 2007-8.
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    Other Issues

    Data has started to be reported from the laboratory testing component of the ASPREN GP sentinel surveillance system. For the next report the ratio of patients presenting with ILI, and who are tested, that test positive for influenza will be reported. For the week ending 3 July, data showed 75% of ILI patients were tested for influenza. The percentage positive and whether they were Pandemic H1N1 2009 is yet to be determined.
    Media have reported this week that Pandemic H1N1 2009 has resulted in large absenteeism rates from businesses in NSW. This is not reflected in the national absenteeism in this report but will be monitored over the coming weeks.

    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 20. The high rates of seasonal influenza seen during May and June are most likely due to the increase in testing for pandemic (H1N1) 2009.

    The total number of confirmed influenza cases started decreasing after 17 June 2009 as result of Australia’s 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.

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

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

    Sources: NNDSS and NetEPI
    NNDSS data excludes all notifications that are identifiable as pandemic (H1N1) 2009 but some influenza A may be pandemic (H1N1) 2009 if subtyping is not carried out by some laboratories.



    The proportion of pandemic (H1N1) 2009 to seasonal influenza varies across jurisdictions. Most jurisdictions have reported that the proportion of positive influenza tests that are 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 average proportion of tests positive for influenza that were pandemic (H1N1) 2009 for the week ending 27 June 2009 was 70% nationally (75% WA, 71% NT, 51% NSW, 99% Vic), an increase from 64% in the previous week.
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    Sentinel Data

    Laboratory surveillance

    The Victorian Infectious Disease Reference Laboratory (VIDRL) has reported that in the week ending 28 June 2009, Influenza A, picornavirus, and respiratory syncytial virus (RSV) were the most commonly detected respiratory viruses in Victoria. The proportion of tests positive for influenza among ILI patients increased from 6% in week 1 of surveillance to 63% in week 9 (for full report see: www.vidrl.org.au).

    South Australia has reported that in the week ending 28 June 2009, influenza A, was the most commonly detected respiratory virus in South Australia.

    New South Wales reported that in the week ending 26 June 2009, seasonal influenza A (H3N2) was the most commonly identified respiratory virus circulating.

    In the week ending 26 June 2009, both the number of virology samples tested in New South Wales and the percentage of tests positive for influenza increased. The percentage of respiratory tests positive for influenza is approximately 25% and is much higher than at the same time in 2007 and 2008 (Figure 2). The expected decrease in testing as a result of the introduction of the PROTECT phase is not yet reflected in this graph.

    Figure 2. Number of All Virology Tests for Respiratory Illness and Percentage of tests positive for influenza, NSW, 2007 to 26 June 2009

    Number of All Virology Tests for Respiratory Illness and Percentage of tests positive for influenza, NSW, 2007 to 26 June 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 28 June 2009 show that ILI consultation rates have increased indicating a greater level of ILI in the community. Rates in recent weeks are following similar trends to those seen in 2007 (Figure 3). In the last week, the presentation rate to sentinel GPs in Australia was approximately 25 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 an increase of ILI consultations to 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 3. Rate of ILI reported from GP ILI surveillance systems from 2007 to 2009, by week
    Rate of ILI reported from GP ILI surveillance systems from 2007 to 2009, by week

    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 decreased over the last few weeks (Figure 4). The number of admissions through EDs of patients with ILI has increased during the period from 22 to 33 admissions.

    Figure 4. Number of Emergency Department presentations due to ILI in Western Australia from 1 January 2007 to 28 June 2009 by week

    Number of Emergency Department presentations due to ILI in Western Australia from 1 January 2007 to 28 June 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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    Paediatric hospital admissions

    The Australian Paediatric Surveillance Unit (APSU) conducts surveillance of severe complications of influenza in children aged 15 years and under. For 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 3 July 2009, APSU reported 11 notifications of children hospitalised with severe complications of influenza. Since reporting began, 21 children have been hospitalised. Of the 11 cases for which data is available, the average age of children admitted to hospital is 2.7 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 that 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 following similar trends to those seen in 2007 and 2008 (Figure 5).

    Figure 5. Absenteeism rates, 1 January 2007 to 17 June 2009, by week

    Absenteeism rates, 1 January 2007 to 17 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 3 July 2009 there were 4713 confirmed cases of pandemic (H1N1) 2009 in Australia. The cumulative number of cases continued to rise in all jurisdictions, although the reported daily rate of notifications declined after 17 June 2009, reflecting the targeted approach to the laboratory testing of suspect cases as part of the PROTECT phase measures.

    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 6). The epidemic curve shows two 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 the change to targeted laboratory testing implemented on 3 June 2009 as part of the modified SUSTAIN phase in Victoria. The reported daily notification rate of confirmed cases in most other jurisdictions increased in the first half of June 2009 and has since declined.
    Figure 6. Temporal distribution of confirmed cases of pandemic (H1N1) 2009 in Australia, by jurisdiction

    Temporal distribution of confirmed cases of pandemic (H1N1) 2009 in Australia, by jurisdiction

    Source: NetEPI


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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.1 Of the 4693 confirmed Australian cases for whom age was known, the median age is 19. The greatest number of cases was reported in the 10–19 year age group and these accounted for 35% (n=1649) of all confirmed cases (Figure 7). Children under five years of age accounted for five per cent (n=238) of cases and people over the age of 60 years accounted for two per cent (n=110) of cases. Again, these 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.

    Males and females in Australia appear to be similarly at risk of infection with pandemic (H1N1) 2009 (Figure 7), consistent with the age and sex distribution of confirmed cases reported in other parts of the world.1

    Figure 7. Laboratory confirmed cases of pandemic (H1N1) 2009 in Australia to 3 July 2009, by age group and sex

    Laboratory confirmed cases of pandemic (H1N1) 2009 in Australia to 3 July 2009, by age group and sex

    Source: NetEPI



    There are some differences in the age distribution among confirmed cases in different states and territories, reflecting the predominance of school based outbreaks in some states and territories or the importation of cases from areas with a high incidence of the disease. In the Northern Territory the proportion of confirmed numbers has increased in the 50 to 59 year age group, of which seventy five per cent are Aboriginal and/or Torres Strait Islander people.

    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 a 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

    The greatest proportion of all cases reported in Australia to 3 July 2009 have occurred in Victoria (37%), followed by New South Wales (24%) and Queensland (16%) (Table 1). Crude rates per capita vary across the jurisdictions, with the greatest rates per 100,000 populations occurring in the Northern Territory, Australian Capital Territory and Victoria. It should also be noted that the crude rates do not take into account differences in population structure.

    Table 1. Notifications and crude rates of laboratory-confirmed pandemic (H1N1) 2009, by jurisdiction to 3 July 2009
    Jurisdiction
    Total H1N1 Influenza 09 notifications Percentage of national H1N1 Influenza 09 notifications Crude notification rate per 100,000 population
    ACT
    186
    3.9%
    54.7
    NSW
    1135
    24.1%
    16.5
    NT
    289
    6.1%
    134.4
    Qld
    760
    16.1%
    18.2
    SA
    169
    3.6%
    10.7
    Tas
    95
    2.0%
    19.3
    Vic
    1743
    37.0%
    33.5
    WA
    291
    6.2%
    13.8
    Aus
    4713*
    100%
    22.4

    *No jurisdiction identifier was available for 45 confirmed cases
    Source: NetEPI


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    Aboriginal and Torres Strait Islander people/communities

    As of the 3 July 2009, six per cent (n=280) of confirmed cases are reported as Aboriginal and/or Torres Strait Islander in the NetEpi database. This population group is overrepresented among confirmed cases as it is estimated that 2.4 per cent of the total Australian population are Aboriginal and/or Torres Strait Islander. Note that in eighteen per cent of the cases (869/4713) the Indigenous field in the NetEpi database has not been completed.

    The median age of Aboriginal and/or Torres Strait Islander confirmed cases is 22 years of age (range 0-58 years of age), compared with a median age of 19 years of age for all Australian cases. Sixty eight per cent (n=189) of confirmed cases are aged less than 30 years of age. Fifty three per cent (n=147) are female and forty five per cent (n=126) are male. No data on gender is available for seven cases.

    Seventy per cent (n=196) of Aboriginal and/or Torres Strait Islander confirmed cases are in the Northern Territory, followed by eighteen per cent (n=51) in Queensland, six per cent (n=18) in New South Wales, three per cent (n=8) in Western Australia and one per cent in Victoria (n=3), Tasmania (n=2) and the Australian Capital Territory (n=2). In the Northern Territory, the number of cases within the Aboriginal population is higher than would be expected given the proportion (30%) of Aboriginal people in the Territory. An increasing number of Aboriginal and/or Torres Strait Islander communities in the Northern Territory are reporting outbreaks of pandemic (H1N1) 2009, with six communities reporting more than ten confirmed cases. Forty seven confirmed cases have been reported in Aboriginal people in Alice Springs.

    Thirty six out of the two hundred and eighty Aboriginal and/or Torres Strait Islander cases are reported as having been hospitalised in the NetEpi database. The majority of these cases (n=27) have been in the Northern Territory, with fourteen per cent of confirmed cases requiring hospitalisation.
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    Severe cases and hospitalisations

    As of 3 July 2009, eight per cent (402/4958) of confirmed cases of pandemic (H1N1) 2009 in Australia have been reported as hospitalised by the jurisdictions. The number of cases per day requiring hospitalisation has been increasing since mid June (Figure 8) and has doubled in the previous week (Week 27). 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. The proportion of cumulative cases requiring hospitalisation compared with the total number of confirmed cases also increased from three per cent on 15 June 2009 to eight per cent on 3 July 2009. 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.

    Twenty one per cent (n=85) of hospitalised cases have been admitted to an intensive care unit (ICU), with the proportion of cases requiring admittance to ICU on any given day ranging from twenty two per cent to thirty nine per cent (Figure 9). It is likely that most cases admitted to an ICU would be ventilated.

    Figure 8. Hospitalisations of pandemic (H1N1) 2009 and proportion of cumulative hospitalised cases compared to cumulative number of cases, 15 June 2009 to 3 July 2009, Australia

    Hospitalisations of pandemic (H1N1) 2009 and proportion of cumulative hospitalised cases compared to cumulative number of cases

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



    Figure 9. Proportion of hospitalised pandemic (H1N1) 2009 confirmed cases admitted to ICU compared to cases hospitalised,* 15 June 2009 to 3 July 2009, Australia

    Proportion of hospitalised pandemic (H1N1) 2009 confirmed cases admitted to ICU compared to 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, 402 confirmed cases have been hospitalised. These numbers are small and the proportion admitted to ICU should be interpreted with caution.
    Source: Jurisdictions


    Eleven people in Australia* with confirmed pandemic (H1N1) 2009 infection had died as of the 3 July 2009 (Figure 6), this is an increase of seven deaths since the last report. The average age of cases who died was 47 years of age (range 3-85 years of age). Most of the cases had underlying medical conditions; including cancer, diabetes mellitus and morbid obesity. Eight (73%) of these cases were male and three (27%) were female.

    * 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


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    Seasonal Influenza Activity in Australia

    Laboratory Confirmed Influenza

    There have been 7,318 cases of laboratory confirmed influenza diagnosed and reported to the National Notifiable Diseases Surveillance System (NNDSS) to 3 July 2009 (Figure 10). There were 1,185 laboratory confirmed influenza cases in the same period last year.

    Influenza notifications are above the 5 year rolling mean for this period (Figure 10). The high notification rates are predominantly due to increased testing for influenza associated with the pandemic (H1N1) 2009 outbreak. Influenza notifications have decreased in this reporting period (Figures 10 and 11). It is likely that this is related to the transition to the PROTECT phase as well as delays in reporting.

    Source: Jurisdictions



    Figure 10. Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 3 July 2009, by jurisdiction and week of diagnosis*

    Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 3 July 2009, by jurisdiction and week of diagnosis

    * NNDSS data excludes all notifications that are identifiable as pandemic (H1N1) 2009 but some influenza A may be pandemic (H1N1) 2009 if subtyping is not carried out by some laboratories.
    SOURCE: NNDSS



    Notifications in 2009 have been predominantly from Victoria (40%), Queensland (24%), New South Wales (14%) and South Australia (10%). The Australian Capital Territory, the Northern Territory, Tasmania and Western Australia accounted for the other 13% (Table 1 and Figure 11).
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    The Northern Territory has reported the highest rate of seasonal influenza notifications per 100,000 population (182) followed by Victoria (57), South Australia (46), the Australian Capital Territory (42) and Queensland (41). All other jurisdictions reported notification rates under 16 per 100,000 population.

    Table 2. Number and rate of laboratory-confirmed notifications by jurisdiction, NNDSS, 1 January 2009 to 3 July 2009*

    State
    Cases Percentage of Total Notifications Rate per 100,000 Average Rate YTD 2004-2008 Percentage of Australian  population*
    ACT
    142
    1.9%
    41.8
    24.4
    1.6%
    NSW
    998
    13.6%
    14.5
    19.4
    32.6%
    NT
    392
    5.4%
    182.3
    40.9
    1.0%
    Qld
    1721
    23.5%
    41.2
    34.5
    20.0%
    SA
    726
    9.9%
    45.8
    8.9
    7.5%
    Tas
    66
    0.9%
    13.4
    14.7
    2.3%
    Vic
    2944
    40.2%
    56.6
    12.1
    24.8%
    WA
    329
    4.5%
    15.6
    21.8
    10.1%
    Aus
    7318
    100%
    34.8
    4.0
    100.00%


    * NNDSS data excludes all notifications that are identifiable as pandemic (H1N1) 2009 but some influenza A may be pandemic (H1N1) 2009 if subtyping is not carried out by some laboratories.
    SOURCE: NNDSS, ABS (2008 populations)
    Source: Jurisdictions


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    Figure 11. Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 3 July 2009, by jurisdiction and week of diagnosis*


    Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 3 July 2009, by jurisdiction and week of diagnosis


    * NNDSS data excludes all notifications that are identifiable as pandemic (H1N1) 2009 but some influenza A may be pandemic (H1N1) 2009 if subtyping is not carried out by some laboratories.
    SOURCE: NNDSS



    National age-specific notification rates year to date show the highest rates of notifications occurred in the 10–14 year age group (Figure 12). Rates of influenza across all ages are markedly different to those seen at the same time in 2008 when the highest rates were observed in children under 12 months and adults over 55 years. This year, rates of influenza are highest in those aged under and this is likely to be a result of increase testing for pandemic (H1N1) 2009 across all age groups (Figure 12).
    Source: Jurisdictions
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    Figure 12. Notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2009 to 3 July 2009, by age group and sex*


    Notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2009 to 3 July 2009, by age group and sex

    * NNDSS data excludes all notifications that are identifiable as pandemic (H1N1) 2009 but some influenza A may be pandemic (H1N1) 2009 if subtyping is not carried out by some laboratories.
    SOURCE: NNDSS


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    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 13). The numbers on the map indicate the number of cases occurring within each region.

    Source: Jurisdictions



    Figure 13. Map of notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2008 to 3 July 2009, by Statistical Division of residence*

    Map of notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2008 to 3 July 2009, by Statistical Division of residence

    * NNDSS data excludes all the identifiable notifications of pandemic (H1N1) 2009. However, there is 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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    Antiviral Resistance Global update

    Although the WHO has not released a report on oseltamivir resistance since 4 June 2009, during the northern hemisphere influenza season 2008-2009, ninety six per cent of seasonal influenza A (H1N1) isolates tested from 36 countries worldwide were resistant to oseltamivir. This indicates a substantial increase in seasonal influenza A (H1N1) resistance to oseltamivir, from the 2007-2008 northern hemisphere influenza season which was fifteen percent.2,3

    The US CDC continues to report that the all the pandemic (H1N1) 2009 viruses tested were susceptible to oseltamivir and zanamivir and resistant to amantadine and rimantadine.4

    Media have reported that an isolate of pandemic (H1N1) 2009 has been identified in Denmark as showing resistance to oseltamivir. Anti-viral resistance is not uncommon in flu viruses, and the World Health Organization (WHO) has stated that the Danish case has no public health implications (i.e. this does not cause changes to the current recommendations for the use of oseltamivir).5

    Media have reported that Japan has identified a case of genetic mutation in the pandemic (H1N1) 2009 virus that shows resistance to oseltamivir in a patient who was given a prophylactic course but who still developed symptoms. The mutated virus does not appear to be spreading and there is no immediate threat to public health.6

    Hong Kong Ministry of Health has confirmed during routine testing that a pandemic (H1N1) 2009 isolate has shown resistance to oseltamivir, but is sensitive to zanamivir.7 The resistant strain was identified in a case who had not been treated with an antiviral, meaning that she was already infected with a resistant strain that was circulating in the community. It is likely that the case acquired the infection in the USA.
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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 3 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 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.

    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 to 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.

    Sentinel Emergency Department (ED) data

    WA ED surveillance data are extracted from the ‘EDSS News’ 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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    Attachments

    International influenza surveillance

    As of 3 July 2009,* the WHO has reported 89921 cases of pandemic (H1N1) 2009 infection, including 382 deaths (a Case Fatality Rate of 0.42%).8

    * WHO has reported a total of 429 deaths this report was compiled. For the most WHO recent figures see http://www.who.int/csr/don/en/



    A number of countries with widespread transmission have either moved (US, Mexico, Chile, Argentina) or are moving (UK) towards a phase similar to the Australian phase PROTECT, where the resources are focused on providing the appropriate treatment to people with pandemic (H1N1) 2009.

    The rate of pandemic (H1N1) 2009notifications in Australia (21.6 per 100,000 population) is similar to that of New Zealand (Table 3). Chile and Canada have higher rates (43.6 and 23.7 respectively per 100,000 population) than Australia, while the rates for UK, the USA, Mexico, Argentina and Japan are lower.

    Table 3. Notification rates for pandemic (H1N1) 2009 in a selection of affected countries9

    Country
    Rate per 100,000 population
    Chile
    43.6
    Canada
    23.7
    Australia
    21.6
    New Zealand
    21.1
    UK
    12.1
    USA
    11.1
    Mexico
    9.4
    Argentina
    4.0
    Japan
    1.1


    The above rates are calculated from the number of confirmed cases for each particular country as provided in the WHO pandemic (H1N1) 2009 report update as at 3 July 09

    Although the rate of confirmed cases per 100,000 population for Argentina is significantly lower than that of Chile, the reported deaths associated with pandemic (H1N1) 2009 are higher (60 confirmed deaths in Argentina, compared to 16 deaths for Chile).10 This could be the result of underreporting of confirmed cases in Argentina. Argentinean media is reporting that some young patients are presenting to health services with pneumonia symptoms who then rapidly deteriorate.11
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    Southern Hemisphere

    During weeks 23-24, there were widespread seasonal influenza outbreaks reported in Brazil and South Africa due to seasonal influenza A(H3). Low levels of influenza B were also detected in Brazil and South Africa.

    In Chile, ILI activity and GP consultations for adult respiratory illness continues to increase more rapidly than in the previous four years.12

    In New Zealand, seasonal influenza A (H1N1) has been the predominant strain of all subtyped isolates and low levels of seasonal influenza A(H3) activity were also reported. All of the 28 seasonal influenza A (H1N1) isolates tested were resistant to oseltamivir.13

    In Hong Kong, since 2009 seasonal influenza reporting commenced influenza A (H3N2) has been the predominant strain of all subtyped isolates. Seasonal influenza activity has remained at baseline levels, however pandemic (H1N1) 2009 cases continue to increase and dominate all influenza subtypes.14
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    Northern Hemisphere

    In the northern hemisphere, seasonal influenza was at or below base line levels, however local seasonal influenza activity was still reported in a number of regions. Canada currently has higher levels of ILI activity when compared to the previous 11 seasons.15

    During the week of 21-27 June 2009, influenza activity decreased in the United States, however there were still higher levels of influenza-like illness than is normal for this time of year. Over 98% of all subtyped influenza A viruses being reported to CDC were pandemic (H1N1) 2009 viruses.16

    From 22 to 28 June 2009, all European countries reporting indicated low levels of seasonal influenza activity except the UK, which reported medium activity.17

    Characteristics of pandemic (H1N1) 2009—global perspectives

    Transmission dynamics

    The basic reproduction number (R0) is the average number of cases generated by a case over the course of their infectious period in a wholly susceptible population. It is useful for estimating the transmission potential of an infectious agent. Three different epidemiological analyses of data from Mexico gave basic reproduction number estimates in the range of 1.4 to 1.6, whereas a genetic analysis gave a central estimate of 1.2.18 This suggests that transmissibility of pandemic (H1N1) 2009 is substantially higher than that of seasonal influenza, and comparable with lower estimates of R0 obtained from previous influenza pandemics.18 A study in Japan estimated the R0 to be as high as 2.3, although the authors suggested that this relatively high value may have been influenced by high contact rates among adolescents.19

    The secondary attack rates of seasonal influenza within households range from 5% to 15%. Current estimates of the secondary household attack rates of pandemic (H1N1) 2009 range from 22% to 33%.1

    Clinical characteristics

    Globally, most cases have been mild, although severe disease has been reported both among known groups at higher risk of adverse outcomes following influenza and in previously healthy young adults, leading WHO to classify the severity of this pandemic to date as ‘moderate’.1
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    References

    1. World Health Organisation: Weekly Epidemiological Record No. 25, 2009. Available at: http://www.who.int/wer/2009/en/; accessed 6 July 2009.
    2. WHO Influenza A virus resistance to oseltamivir and other antiviral medicines, 4 June 2009. Available from:
    http://www.who.int/csr/disease/influenza/2008-9nhemisummaryreport/en/index.html. Accessed 3 July 2009.
    3. WHO Influenza A (H1N1) virus resistance to oseltamivir – Last quarter 2007 to 2 June 2008.
    Available from: http://www.who.int/csr/disease/influenza/ResistanceTable200806013.pdf Accessed 3 July 2009.
    4. CDC Influenza reports http://www.cdc.gov/h1n1flu/pubs/ Accessed 3 July 2009.
    5. Reuters news: http://www.reuters.com/article/healthNews/idUSTRE55S3UM20090629 Accessed 2 July 2009.
    6. Reuters news: http://www.reuters.com/article/rbssPharmaceuticals%20-%20Diversified/idUSSP52739320090702 Accessed 2 July 2009.
    7. 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.
    8. World Health Organisation: Pandemic (H1N1) 2009 report update 57 (3 July 2009). Available at: http://www.who.int/csr/disease/swineflu/updates/en/index.html
    9. World Health Organisation: Pandemic (H1N1) 2009 report update 57 (3 July 2009). Available at: http://www.who.int/csr/disease/swineflu/updates/en/index.html
    10. PanAmerican Health Organization, 6 July 2009. Available from: http://new.paho.org/hq/index.php?option=com_content&task=view&id=1570&Itemid=1167
    11. Media release, 28 June 2009. Available at http://crofsblogs.typepad.com/h5n1/2009/06/argentina-lungs-that-burn-in-hours.html
    12. Pan American Health Organization. Weekly monitoring of Pandemic H1N1 2009 in the Americas Region. June 29th, 2009.
    13. New Zealand Public Health Surveillance Weekly Influenza Update, weeks 24 & 25. Available from: http://www.surv.esr.cri.nz/virology/influenza_weekly_update.php Accessed 2 July 2009.
    14. Flu Express, weeks 24 & 25. Available from: http://www.chp.gov.hk/guideline1_year.asp?lang=en&id=304&pid=134&ppid=29. Accessed 3 July 2009.
    15. Pan American Health Organization. Weekly monitoring of Pandemic H1N1 2009 in the Americas Region. June 29th, 2009.
    16. CDC Influenza reports http://www.cdc.gov/h1n1flu/pubs/ Accessed 3 July 2009.
    17. EISS Weekly Electronic Bulletin Influenza Season 2008-2009, week 26.
    Available from: http://ecdc.europa.eu/en/Activities/Surveillance/EISN/ Accessed 6 July 2009.
    18. Fraser C et al. Pandemic potential of a strain of influenza A (H1N1): early findings. Science Express, 11 May 2009 – doi: 10.1126/science.1176062. Available at http://www.sciencemag.org/cgi/content/full/324/5934/1557; accessed 23 June 2009.
    19. Nishiura H et al. Transmission potential of the new influenza A (H1N1) virus and its age-specificity in Japan. Eurosurveillance, 2009, 14(22):pii=19227. Available at http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19227; accessed 23 June 2009.