Australian influenza report 2009 - 25 - 31 July 2009 (#12/09)

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: 18 August 2009

Report No. 12
Week ending 31 July 2009

A print friendly version of this report is available as a PDF (208 KB)

Key Indicators



Is the situation changing?
Indicated by: laboratory confirmed cases reported to NetEpi/NNDSS; GP Sentinel ILI Surveillance; and ED presentations of ILI at sentinel hospitals (NSW and WA).
The counting of every case of pandemic influenza is no longer feasible in the PROTECT phase. Influenza activity, including influenza like illness (ILI) activity in the community is monitored by various surveillance systems.
Laboratory data are used to determine the proportion of pandemic A H1N1 circulating in the community.
How severe is the disease, and is severity changing?
Indicated by: number of hospitalisations, ICU admissions and deaths from sentinel hospital surveillance; emergence of more severe clinical picture in hospitalised cases and ICU admissions.
Is the virus changing?
Indicated by: emergence of drug resistance or gene drift/shift from laboratory surveillance.
What is ahead?
Forward projections of cases, morbidity and mortality.


Top of page

Key Points

As of 31 July 2009 there were 20,747 confirmed cases of pandemic (H1N1) 2009 in Australia, including 61 deaths. Notifications of laboratory confirmed pandemic (H1N1) 2009 has decreased nationally over the last week. All jurisdictions except Victoria and New South Wales have reported that they believe that they have yet to reach their peak. The number of cases reported is only a small proportion of pandemic (H1N1) 2009 circulating in the community.

Is the situation changing?

  • Overall, current national influenza activity is still increasing. Activity varies across jurisdictions.
  • Nationally, laboratory confirmed influenza notifications continue to increase.
  • ILI presentations to General Practitioners remain high and comparable to 2007 rates nationally. Decreases have been seen in Victoria and South Australia this reporting period.
  • Trends in the rates of ILI presentations to Emergency Departments varied this reporting period, with WA, SA and the ACT reporting an increase and NSW and NT reporting a decrease.
  • Absenteeism rates have increased in the last week, and are at similar levels to those seen at the same time in 2007.
  • Available information indicates about two thirds of cases of ILI are not due to influenza.
  • The pandemic strain appears to be replacing the current seasonal H1N1 virus. The proportion of influenza positive tests that were pandemic (H1N1) 2009 continues to increase and varied between jurisdictional reporting systems from 69% (NT) to 100% (Vic sentinel GP system) for this reporting period.
  • Type A is the predominant seasonal influenza type reported by all jurisdictions. Of the seasonal influenza A notifications, A/H3N2 is the predominant subtype reported by most jurisdictions.
    Top of page

    How severe is the disease?

  • The number of people with pandemic (H1N1) 2009 requiring hospitalisation continues to increase. As of 31 July there were 413 people in hospital, and 108 (26.2%) in ICU. In total, 2,525 people have been hospitalised.
  • Over the last week, the average proportion of hospitalised cases in an ICU* on any day was 27%, this has decreased from 40% in the previous week
  • The highest hospitalisation rate occurred in young children aged less than 5 years of age. There are also higher rates in hospitalisation among people aged 50 to 60 years.
  • 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. Indigenous Australians are approximately 5 times more likely than non-Indigenous Australians to be hospitalised for pandemic (H1N1) 2009. In total, 268 (10.6%) hospitalisations have been Indigenous Australians.
  • Three per cent of hospitalisations have been reported as pregnant, reinforcing the fact that pregnancy, particularly in the second and third trimesters, is a risk factor for pandemic H1N1 2009 infection.
  • In the week ending 30 July 2009 the Australian Paediatric Surveillance Unit (APSU) reported no notifications of children hospitalised with severe complications of influenza.
  • The number of people dying with pandemic (H1N1) 2009 continues to increase. As of 31 July, 61 people have died. Of these deaths, one was a pregnant woman and 6 (9.8%) were Indigenous.
  • The median age of confirmed cases that died is 54 years (range 3-86 years of age), compared to the media age for deaths from seasonal flu from 2001 to 2006 which is 83 years.
  • Reports from the jurisdictions in Australia indicate that most of the deaths had underlying medical conditions; including cancer, diabetes mellitus and morbid obesity.

    * Most cases admitted to an ICU would be ventilated.


    Top of page

    Is the virus changing?

    To date in Australia, all of the 78 pandemic influenza isolates tested are sensitive to the neuraminidase inhibitors oseltamivir and zanamivir.

    The proportions of Australian seasonal influenza isolates that are resistant to oseltamivir are: 97% of seasonal A/H1N1 isolates, 0% of A/H3N2 isolates, 0% of Type B isolates. None have tested resistant to zanamivir.
    Top of page

    Current influenza activity in Australia – Is the situation changing?

    Total laboratory confirmed influenza

    Nationally, laboratory confirmed influenza notifications continue to increase. As numbers have increased some laboratories have reduced the amount of subtyping conducted. As a result the proportion of influenza A notifications has increased. These may be seasonal influenza A or pandemic (H1N1) 2009.

    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 (starting 16 May 2009). The high number 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 means that the number of confirmed cases will not reflect how many people in the community have acquired pandemic (H1N1) 2009 infection, but reflects the number of confirmed cases among those most at risk.

    Figure 1: Influenza activity in Australia, by reporting week, years 2007, 2008 and 2009*

    Influenza activity in Australia, by reporting week, years 2007, 2008 and 2009

    * Data on pandemic (H1N1) 2001 cases is extracted from NetEPI; data on seasonal influenza is extracted from the NNDSS.
    Sources: NNDSS and NetEPI databases


    Top of page

    Pandemic (H1N1) 2009 Influenza activity in Australia

    As of 31 July 2009 there were 20,747 confirmed cases of pandemic (H1N1) 2009 in Australia, including 61 deaths. Notifications of laboratory confirmed pandemic (H1N1) 2009 has decreased nationally over the last week. All jurisdictions except Victoria and New South Wales have reported that they believe that they have yet to reach their peak. The number of cases reported is only a small proportion of pandemic (H1N1) 2009 circulating in the community.

    The national epidemic curve shows the jurisdictional distribution of confirmed cases of pandemic (H1N1) 2009 over time in Australia (Figure 2). The epidemic curve shows several peaks, however the pattern is a surveillance artefact due to a change in testing policy. The majority of earlier confirmed cases occurred in Victoria, where case reporting peaked in late May before declining rapidly in early June. This change was due to targeted laboratory testing implemented on 3 June 2009 as part of the modified SUSTAIN phase.

    Figure 2. Laboratory confirmed cases of pandemic (H1N1) 2009 in Australia, to 31 July 2009 by jurisdiction

    Laboratory confirmed cases of pandemic (H1N1) 2009 in Australia, to 31 July 2009 by jurisdiction

    Source: NetEPI database


    Top of page

    Influenza Like Illness activity in Australia

    Sentinel General Practice



    ILI presentations to General Practitioners remain high and comparable to 2007 rates nationally. Decreases have been seen in Victoria and South Australia this reporting period.

    Combined data available from the Australian Sentinel Practices Research Network (ASPREN), the Northern Territory GP surveillance system and VIDRL, up until 26 July 2009, show that nationally, influenza like Illness (ILI) consultation rates have dropped this reporting period to below levels seen in 2007 (Figure 3). In the last week, the presentation rate to sentinel GPs in Australia was approximately 33 cases per 1,000 patients seen.

    Figure 4a does not include GPs from Victoria reporting to ASPREN or VIDRL. Consultation rates of ILI (excluding Victoria) are higher than in 2007 and 2008, but have dropped slightly in this reporting period. Further analysis of the ILI data showed South Australian levels dropped in this period. Figure 4b shows that while overall the ILI presentation rates may have peaked in Victoria. Rates of ILI from Victorian ASPREN GPs have increased while rates reported by VIDRL GPs have dropped.

    Figure 3. Rate of ILI reported from GP ILI surveillance systems from 2007 to 26 July 2009 by week*

    Rate of ILI reported from GP ILI surveillance systems from 2007 to 26 July 2009 by week

    * Delays in the reporting of data may cause data to change retrospectively. As data from the NT and the VIDRL surveillance systems are combined with ASPREN data, rates may not be directly comparable across 2007, 2008 and 2009.
    SOURCE: ASPREN, NT, VIDRL


    Top of page
    Figure 4a. Rate of ILI reported from ASPREN and NT (excluding VIC) from 2007 to 26 July 2009 by week

    Rate of ILI reported from ASPREN and NT (excluding VIC) from 2007 to 26 July 2009 by week

    SOURCE: ASPREN, NT



    Figure 4b. Rate of ILI reported from VIC GPs reporting to ASPREN and VIDRL up to 26 July 2009 by week

    Rate of ILI reported from VIC GPs reporting to ASPREN and VIDRL up to 26 July 2009 by week

    SOURCE: ASPREN (VIC) & VIDRL


    Top of page
    Emergency departments
    Trends in ILI presentations to EDs varied this reporting period, with WA (Figure 5), SA and the ACT reporting an increase and NSW (Figure 6) and NT reporting a decrease.

    The number of ILI presentations reported in Western Australian EDs has increased in the week ending 26 July 2009, with a slower rate of increase compared to previous periods (Figure 5). The proportion of ILI presentations admitted to hospital increased from 4.3% to 5.7%.

    Figure 5. Number of Emergency Department presentations due to ILI in Western Australia from 1 January 2007 to 26 July 2009 by week

    Number of Emergency Department presentations due to ILI in Western Australia from 1 January 2007 to 26 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 ‘Virus Watch’ Report



    In the week ending 24 July 2009, ILI presentations to New South Wales EDs decreased (rate 38 per 1,000 presentations) (Figure 6). Presentations were mainly for mild illnesses and 8% of presentations with ILI were admitted.

    Figure 6. Rate of ILI diagnosed in people presenting to selected Emergency Departments, NSW 1 January 2005 to 24 July 2009 by month*

    Rate of ILI diagnosed in people presenting to selected Emergency Departments, NSW 1 January 2005 to 24 July 2009 by month

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



    ILI presentations to South Australian EDs increased this reporting period from 180 to 217, the number of admissions also increased from 7 to 13.
    Top of page
    Absenteeism
    Absenteeism rates have increased in the last week and are much higher than at the same time in 2008 but at around the same level as in 2007 (Figure 7).

    Figure 7. Rates of absenteeism of greater than 3 days absent, National employer, 1 January 2007 to 15 July 2009, by week[

    Rates of absenteeism of greater than 3 days absent, National employer, 1 January 2007 to 15 July 2009, by week

    SOURCE: Absenteeism data


    Top of page
    Laboratory surveillance
    Proportion of Laboratory Confirmed Influenza Pandemic (H1N1) 2009 to seasonal influenza
    Influenza A was the most commonly detected respiratory viruses reported by sentinel laboratories in Victoria, South Australia and New South Wales. Respiratory syncytial virus (RSV) and picornavirus were also common.

    As shown in Table 1, the overall trend in virology testing is generally increasing. The proportion of respiratory tests positive for influenza varied between jurisdictional reporting laboratories from 24% and 41% for this reporting period.

    Table 1. Percentage of laboratory tests that tested positive for influenza

      17 / 19 July 24 / 26 July

     

    Number tested % positive for influenza Number tested % positive for influenza
    ASPREN – national*
    112
    42%
    80
    41%
    NSW Sentinel Labs
    3356
    30.8%
    3755
    24%
    WA NIC
    1777
    29.6%
    2143
    32%
    VIDRL Sentinel GPs
    68
    43%
    59
    41%

    * ASPREN tests are collected every Tuesday. Results are reported for a rolling fortnight as data changes retrospectively.


    Top of page
    The proportion of influenza positive tests that were pandemic (H1N1) 2009 continues to increase and varied between jurisdictional reporting laboratories from 69% (NT) to 100% (Victoria) for this reporting period (Table 2).

    The proportion of pandemic (H1N1) 2009 to seasonal influenza varies across jurisdictions and continues to increase. Recent reports from jurisdictional sources in New South Wales sentinel laboratories (70.4%, week ending 24 July), Victoria NIC (92%, week ending 31 July), VIDRL Sentinel GP (100%, week ending 26 July), Western Australia NIC (92%, week ending 26 July) and the Northern Territory (68.9%, week ending 31 July) showed that the average proportion of confirmed influenza in Australia which was pandemic (H1N1) 2009 was just over 80%. (Table 2)

    Over the last two weeks, for the days on which surveillance testing was conducted, ASPREN GPs reported 129 people presenting with ILI. Of these, 62% (80/129) were tested for influenza. Forty-one per cent (33/80) of these cases were influenza positive; 88% (29/33) were pandemic (H1N1) 2009 and 12% (4/33) were influenza A unspecified.

    Table 2. Percentage of laboratory tests that tested positive for pandemic (H1N1) 2009

      17 / 19 July 24 / 26 July

     

    Number of positive tests for influenza % positive for pandemic (H1N1) 2009 Number of positive tests for influenza % positive for pandemic (H1N1) 2009
    ASPREN – national*
    30
    83% (25)
    33
    88% (29)
    NSW Sentinel Labs
    1037
    59% (607)
    911
    70% (642)
    WA NIC
    526
    85% (420)
    519
    92% (496)
    NT NIC
    191
    82% (157)
    54
    69%(51)
    VIC (NIC)
    n/a
    n/a
    88
    92% (74)**
    VIDRL Sentinel GPs
    29
    90% (26)
    24
    100% (24)


    *ASPREN tests are collected every Tuesday. On Tuesdays 14 July and 21 July, 30 samples tested positive for influenza, while on Tuesdays 21 July and 28 July, 33 samples tested positive for influenza.
    ** 8 Flu A were untyped



    The proportion of pandemic (H1N1) 2009 compared with seasonal influenza in Australia is very similar to that reported by a number of other countries in both the Northern and Southern Hemispheres. Canada is reporting that pandemic (H1N1) 2009 represents 98.7% of all influenzas,1 while Chile is reporting that 93% of the total circulating influenza viruses in people aged over 5 years are pandemic (H1N1) 2009.2 In New Zealand, pandemic (H1N1) 2009 represents 68% of influenza viruses reported from sentinel surveillance and 61% of influenza viruses reported in non-sentinel surveillance.3
    Top of page

    How severe is the disease, and is severity changing?

    Pandemic morbidity (hospitalisations)

    Hospitalisations of Pandemic (H1N1) 2009 confirmed cases[

    As of 31 July 2009, the jurisdictions have reported that 2,525 confirmed cases of pandemic (H1N1) 2009 have been hospitalized (this figure include people who are hospitalized for associated conditions). The number of cases per day requiring hospitalisation has been increasing since mid June and 649 additional cases have been hospitalised over the last week.*

    * The numbers hospitalised should be treated with caution as there may be case ascertainment bias in the reporting of confirmed cases being hospitalized. All paediatric cases admitted to hospital are being tested for pandemic (H1N1) 2009 while not all adults are tested. There may be a significant underestimation of the numbers of adults hospitalized from pandemic (H1N1) 2009 due to limited testing.



    Indigenous Australians are approximately 5 times more likely than non-Indigenous Australians to be hospitalised for pandemic (H1N1) 2009. The states and territories have reported that 268 (10.6%) of all 2,525 cases hospitalised since the beginning of the outbreak were Aboriginal and/or Torres Strait Islander.

    The proportion of all cases that required hospitalisation compared with the total number of confirmed cases increased from 3% on 15 June 2009 to 12% on 31 July 2009. This figure has remained relatively constant for the last couple of weeks and 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 hospitalization (Figure 8).

    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

    * ICD10-AM codes J10, J11
    ** ICD10-AM codes J12-J18



    Figure 8. Hospitalisations of pandemic (H1N1) 2009 and proportion of cumulative hospitalised cases compared with cumulative number of cases, 15 June 2009 to 31 July 2009, Australia

    Hospitalisations of pandemic (H1N1) 2009 and proportion of cumulative hospitalised cases compared with cumulative number of cases, 15 June 2009 to 31 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


    Top of page

    Age and sex distribution of hospitalised confirmed cases

    Limited further information is available for 1,547 (61%) of the 2,525 hospitalised confirmed cases. Of these cases, the highest hospitalisation rates are in males aged less than 5 years of age (24.9 per 100,000 population). Figure 9 illustrates that the age distribution of hospitalized cases of pandemic (H1N1) 2009 is different to previous influenza seasons. Young children aged less than 5 years of age continue to be hospitalised at a higher rate than other age groups but for pandemic (H1N1) 2009 there is a peak in the 50 to 60 years age group and a marked decrease in those aged more than 75 years.

    As a comparison with hospitalised confirmed cases in the United Kingdom (n=840) to 23 July 2009, identical proportions have been hospitalised in those aged less than 5 years of age (20%); Australia has higher proportions in the 16-64 year age group (61% compared with 52%); and only 8% of Australian hospitalised cases are aged 65+ years compared with 18% in the United Kingdom.

    Figure 9. Age specific rates of hospitalised confirmed cases of pandemic (H1N1) 2009 to 31 July 2009, compared with average annual age specific rates of hospitalisations from seasonal influenza 2004-05 to 2006-07*, Australia

    Age specific rates of hospitalised confirmed cases of pandemic (H1N1) 2009 to 31 July 2009, compared with average annual age specific rates of hospitalisations from seasonal influenza 2004-05 to 2006-07*, Australia

    * The rates for pandemic (H1N1) 2009 are for a six week period 15 June to 24 July 2009 whereas the rates for seasonal influenza are averaged annual rates (i.e. for a full influenza season).
    Source: NETEPI database


    Top of page

    Pregnancy as a risk factor for pandemic (H1N1) 2009

    Forty seven (3%) of the 1,547 hospitalised confirmed cases for whom further information was known were pregnant women. Thirteen per cent (n=6) were in their first trimester (weeks 1-12); 28% (n=13) were in their second trimester (weeks 13-26); and 60% were in their third trimester (weeks 27-40) (Figure 10). Eight of the 47 pregnant women were admitted to ICU, all in their second or third trimester. One pregnant woman is known to have died.

    Figure 10. Hospitalised confirmed cases of pandemic (H1N1) 2009 in pregnant women by weeks of gestation, to 31 July 2009, Australia

    Hospitalised confirmed cases of pandemic (H1N1) 2009 in pregnant women by weeks of gestation, to 31 July 2009, Australia

    Source: NETEPI database



    Top of page

    Paediatric hospital admissions

    There were no influenza notifications in the week up to 30 July 2009 reported by the Australian Paediatric Surveillance Unit (APSU).

    Since reporting began in 2009, 43 children have been reported as hospitalised with complications from influenza. Of the 32 cases for which data is available, the average age of children admitted to hospital was three years, with an age range from one month to 16 years. Complications were mostly pneumonia and encephalitis. Thirteen of the 24 (54%) cases for which data is available had underlying conditions.

    Confirmed cases requiring intensive care[

    In Week 31 (week ending 31 July 2009), an average of 105 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. Over the last week, the average proportion of hospitalised cases in an ICU Most cases admitted to an ICU would be ventilated. on any day was 27%, this has decreased from 40% in the previous week (Figure 11). This is much higher than figures from the United Kingdom for 22 July 2009, where 8% of hospitalised cases required critical care beds.5

    Figure 11. Proportion of hospitalised pandemic (H1N1) 2009 confirmed cases admitted to ICU compared with cases hospitalised,* 15 June 2009 to 31 July 2009, Australia

    Proportion of hospitalised pandemic (H1N1) 2009 confirmed cases admitted to ICU compared with cases hospitalised, 15 June 2009 to 31 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


    Top of page

    Snapshot on Queensland hospitalised confirmed cases

    Five hundred and sixty four people have been hospitalised in Queensland for pandemic (H1N1) 2009 between 25 May 2009 and 31 July 2009, an age standardised rate of 13.1 per 100,000 population. Fifty five per cent (n=313) of hospitalisations were in females, an age standardised rate of 14.6 per 100,000 population. Forty five per cent (n=251) of hospitalisations were in males, an age standardised rate of 11.6 per 100,000 population.

    Of these 564 hospitalised cases, co-morbidities were reported in 61% (n=345) of cases. Co-morbidities included chronic respiratory 46% (n=160); diabetes 13% (n=45); pregnancy 11% (n=38); chronic cardiac 10% (n=36); immunocompromised 10% (n=36); morbid obesity 8% (n=26); and renal 5% (n=16). Information on the length of time between onset of symptoms and admittance to hospital were available for 379 confirmed cases. Fifty one per cent (195/379) of these cases were admitted within 48 hours of onset of symptoms.

    Figure 12 illustrates that the 0-4 years age group is more likely to be hospitalised but that the length of stay is usually of less than 3 days duration. Twenty three per cent (n=127) of cases were hospitalised for less than 3 days; 39% (n=222) for 3-7 days; 11% (n=61) for 8-13 days; and 7% (n=37) for 14 or more days. These figures include cases that are still hospitalised.

    Of these hospitalised cases, 76 were admitted to an ICU or special care with twice as many male being admitted than females. Seventy six per cent (n=51) of cases were in ICU for 1-10 days (range 1-29 days). The age of cases admitted to ICU ranged from 0-84 years with the highest number of cases in the age groups 25-29 years and 50-54 years, which each accounted for 16% (n=12) of the cases. Thirty nine per cent (n=30) of cases in ICU had no reported co-morbidities.

    Figure 12. Hospitalised confirmed cases of pandemic (H1N1) 2009, by length of hospital stay and age group, to 31 July 2009, Queensland

    Hospitalised confirmed cases of pandemic (H1N1) 2009, by length of hospital stay and age group, to 31 July 2009, Queensland

    Source: Qld Health


    Top of page

    Influenza mortality

    Deaths associated with pandemic (H1N1) 2009

    Sixty one people in Australia* with confirmed pandemic (H1N1) 2009 infection died between 19 June 2009 and 31 July 2009, with 22 reported in New South Wales, 17 in Victoria, eight in Queensland, six in South Australia, three both in the Northern Territory and Tasmania and two in Western Australia. Reports from the jurisdictions in Australia indicate that most of the cases had underlying medical conditions; including cancer, diabetes mellitus and morbid obesity. Of the 61 deaths, 6 (9.8%) were Indigenous.

    * 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



    Further information was available on 46 of the 61 deaths in Australia. Sixty one per cent (n=28) of deaths were in males. The median age of confirmed cases that died was 54 years (range 3-86 years of age). This compares with deaths from seasonal influenza where the median age, for the period 2001-2006, was 83 years. As illustrated in Figure 13, the highest proportion of deaths (35%) have occurred in the 25-49 year age group (n=16), followed by 28% in both the 50-64 year age group (n=13) and 65+ year age groups (n=13), and 9% in the 0-20 year age group (n=4). This is similar to the proportion of deaths in hospitalised cases in the USA. The CDC reported that the number of deaths was highest among people 25-49 years of age (39%), followed by people aged 50-64 years of age (25%) and people aged 5-24 years of age (16%). The CDC also commented that for seasonal influenza an estimated 90% of deaths occur in people aged 65 years and older.

    The pattern of deaths in the different age groups is very different to the age.

    Figure 13. Numbers of deaths among confirmed cases of pandemic (H1N1) 2009, by age group and sex, compared with total pandemic (H1N1) 2009 notifications by age group, to 24 July 2009, Australia

    Numbers of deaths among confirmed cases of pandemic (H1N1) 2009, by age group and sex, compared with total pandemic (H1N1) 2009 notifications by age group, to 24 July 2009, Australia

    Source: NETEPI database


    Top of page

    Deaths associated with influenza and pneumonia

    There are difficulties estimating the number of deaths due to influenza in Australia. Deaths coded as being due to laboratory confirmed influenza are known to underestimate the true number. Influenza may not be listed on the death certificate if it wasn’t recognised as the underlying cause. Coding of pneumonia and influenza provides an additional measure, although this will overestimate the number of deaths, as it will include other causes of pneumonia.

    The median number of annual deaths in Australia for the years 2001 to 2006 from influenza and pneumonia is 3,089. Forty Australians who died had laboratory diagnosed influenza. In 2007 (the latest year for which data has been released) there were 2,623 deaths attributed to influenza and pneumonia as the underlying cause of death. In 2007, influenza and pneumonia was the 13th leading cause of death in Australia (Source: ABS, Causes of Death 2007). Mortality figures are likely to be an underestimate due to inherent difficulties in assigning causes of death and therefore appropriate ICD codes. ABS mortality data are released two years in arrears.

    In Western Australia, in the final week of June, pneumonia and influenza deaths accounted for 19.9% of all deaths compared to 15.5% for the same time in 2008 (Figure 14).

    Figure 14: Total number of deaths classified as influenza and pneumonia, WA Registry of Births, Deaths and Marriages, 1 January 2008 to 27 June 2009

    Total number of deaths classified as influenza and pneumonia, WA Registry of Births, Deaths and Marriages, 1 January 2008 to 27 June 2009

    SOURCE: WA ‘Virus Watch’ Report


    Top of page
    In NSW, death certificate data as of 10 July 2009 show that there were 136 influenza or pneumonia deaths per 1,000 deaths in NSW, which was below the expected seasonal threshold for this time of year of 153 per 1,000 (Figure 15).

    Figure 15: Rates of deaths classified as influenza and pneumonia, NSW Registry of Births, Deaths and Marriages, 1 January 2004 to 10 July 2009

    Rates of deaths classified as influenza and pneumonia, NSW Registry of Births, Deaths and Marriages, 1 January 2004 to 10 July 2009

    SOURCE: NSW Health ‘Weekly Influenza Epidemiology Report’


    Top of page

    Is the virus changing?

    Laboratory Confirmed Influenza

    While total influenza activity in NNDSS in 2009 is 10.6 times higher than the 5-year weekly rolling mean, it is not possible to determine accurately the number of notifications due to seasonal influenza.

    Increasingly, not all influenza viruses are subtyped and the large proportion of influenza A (11,966 notifications) reported to NNDSS could be either pandemic (H1N1) 2009 or seasonal influenza. Laboratory reports in recent weeks estimate that 80% of all influenza positive tests are due to pandemic (H1N1) 2009 but this has varied since the start of the pandemic.

    From 1 January to 31 July 2009, type A is the predominant seasonal influenza type reported by all jurisdictions of cases that do have influenza. Of type A notifications for which there is subtyping information in NNDSS, 1.8% (217) are seasonal H1N1 and 2.9% (352) are H3N2.
    Top of page

    Antigenic characteristics

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

    In 2009 up to 2 August 2009, 526 Australian influenza isolates have been subtyped by the WHO CC in Melbourne. Of these, 223 influenza isolates have been antigenically characterized.
    In general, seasonal influenza A strains circulating this influenza season are the same as strains in the vaccine, with the A(H3N2) virus showing some drift. Influenza B strains match more closely with those in the 2009-10 Northern Hemisphere vaccine.

    Antiviral resistance

    Pandemic (H1N1) 2009

    WHO reported on 4 August 2009 that a total of 6 pandemic (H1N1) 2009 influenza isolates resistant to oseltamivir have now been detected: one from Denmark, one Hong Kong, one from Canada and three from Japan. All patients had received oseltamivir with the exception of one and have recovered well. All resistant viruses had the characteristic mutation at position 274/275 associated with resistance.6

    Media reported on 29 July that in Viet Nam at least four A/H1N1 flu patients had not responded normally to treatment at the HCM City Tropical Diseases Hospital.7
    All the 78 Australian Pandemic (H1N1) 2009 isolates tested for resistance to oseltamivir up to 5 August 2009 have been sensitive to oseltamivir.
    In New Zealand, all the 26 pandemic (H1N1) 2009 viruses tested up to 19 July 2009 continue to be sensitive to oseltamivir.8
    The US CDC reported in the week ending 18 July that all the pandemic (H1N1) 2009 viruses tested were susceptible to oseltamivir and zanamivir, and resistant to amantadine and rimantadine.9

    Seasonal Influenza

    The last WHO report on oseltamivir resistance to seasonal strains was released on 4 June 2009, during the Northern Hemisphere influenza season 2008-2009. This report stated that 96% of seasonal influenza A (H1N1) isolates tested from 36 countries worldwide were resistant to oseltamivir, indicating a substantial increase in seasonal influenza A (H1N1) resistance to oseltamivir from 15% in the 2007-2008 Northern Hemisphere influenza season.10,11

    In New Zealand, all of the 53 seasonal influenza A (H1N1) isolates tested up to 19 July 2009 were resistant to oseltamivir12
    The US CDC reported in the ending 18 July that 99.5% of the seasonal A(H1N1) tested was resistant to oseltamivir and 100% of the Influenza A(H3N2) tested was resistant to adamantanes.1
    Top of page

    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 27 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 ‘Virus Watch’ Report. This report is provided weekly. The Western Australia Influenza Surveillance Program collects data from 8 Perth Emergency Departments (EDs).

    NSW - ED surveillance data are extracted from the ‘NSW Influenza Surveillance Report’. This report is provided weekly. The New South Wales Influenza Surveillance Program collects data from 49 EDs across New South Wales.

    SA – ED surveillance data are extracted from the ‘South Australian Seasonal Influenza Report’. This report is provided weekly. The South Australian Influenza Surveillance Program collects data from 4 EDs in South Australia.
    Top of page

    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.

    Mortality data

    Mortality data are extracted from the NSW Health ‘Weekly Influenza Epidemiology Report’ and the WA ‘Virus Watch’ Report.

    Paediatric hospital admissions data

    Reports of ICU admissions are provided to the Surveillance Branch on a weekly basis by the Australian Paediatric Surveillance Unit. APSU conducts surveillance of severe complications of influenza in children aged 15 years and under. Surveillance began on 1 June 2009.
    Top of page

    References

    1. Canada Public Health Agency, Flu Watch: http://www.phac-aspc.gc.ca/fluwatch/08-09/. Accessed 17 July 2009.
    2. Sociedad Chilena de Infectologia. Available at http://www.sochinf.cl/sitio/. Accessed 30 July 2009.
    3. New Zealand Public Health Surveillance, Influenza Weekly Updates. Available at: http://www.surv.esr.cri.nz/virology/influenza_weekly_update.php. Accessed 30 July 2009.
    4. Australian Institute of Health and Welfare (AIHW) National Hospital Morbidity Database. Available at: http://www.aihw.gov.au/hospitals/datacubes/index.cfm
    5. Letter ‘Pandemic Flu Service’ from CMO, 23 July 2009. UK Department of Health.
    6. WHO Pandemic (H1N1) 2009 - update 60. Available from: http://www.who.int/csr/don/2009_08_04/en/index.html. Accessed 5 August 2009.
    7. Vietnam Net Bridge News, H1N1 flu shows sign of resistance to treatments. Available from: http://english.vietnamnet.vn/Health/2009/07/860674/. Accessed 30 July2009
    8. New Zealand Public Health Surveillance, Influenza Weekly Updates. Available at: http://www.surv.esr.cri.nz/virology/influenza_weekly_update.php Accessed 30 July 2009.
    9. CDC Influenza reports http://www.cdc.gov/h1n1flu/pubs/. Accessed 30 July 2009.
    10. WHO Influenza A virus resistance to oseltamivir and other antiviral medicines, 4 June 2009. Available from:
    http://www.who.int/csr/disease/influenza/en/. Accessed 30 July 2009.
    11.
    12. New Zealand Public Health Surveillance, Influenza Weekly Updates. Available at: http://www.surv.esr.cri.nz/virology/influenza_weekly_update.php. Accessed 30 July 2009.
    13. CDC Influenza reports http://www.cdc.gov/h1n1flu/pubs/. Accessed 30 July 2009.