Australian influenza report 2009 - 30 May to 16 June 2009 (#6/09)

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: 01 July 2009

Report No. 6
Week ending 16 June 2009

A print friendly version of this report is available as a PDF (89 KB)

Prepared by the Vaccine Preventable Disease Surveillance Section

Disclaimer
This report aims to increase awareness of 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, this report is based on data available as at 12 June 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


In this report

  • Influenza notifications in Australia continue to rise, a reflection of ongoing transmission of H1N1 Influenza 09 in the Australian population and increased surveillance associated with the H1N1 Influenza 09 pandemic.
    • Confirmed cases of H1N1 Influenza 09 have been reported in all jurisdictions, with the per capita rates being highest in Victoria, the Northern Territory and the Australian Capital Territory.
    • The age distribution of confirmed cases is skewed towards younger age groups, with 80% of confirmed cases occurring in people under the age of 30. Approximately equal numbers of females and males are affected.
    • Risk factors for severe diseases associated with H1N1 Influenza 09 infection may include chronic heart or lung disease, diabetes, obesity, immunosuppression and pregnancy.
    • A total of 14 cases of H1N1 Influenza 09 have been reported in Aboriginal and/or Torres Strait Islander people, although community transmission among predominantly indigenous communities has not been reported.
    • The vast majority of confirmed cases have reported mild symptoms of fever and respiratory illness similar to those of seasonal influenza. The transition to PROTECT Phase, however, means that testing will be directed to identification of H1N1 Influenza 09 in people with moderate or severe illness.
  • Syndromic and laboratory surveillance indicates that the influenza season has not yet commenced in the Australian community.
    • Seasonal influenza notifications rates are highest in the 10-14 and 15-19 year age groups.
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    Influenza in Australia

    Influenza notifications are above the 5 year rolling mean for this period (Figure 1). The influenza notifications for weeks 17-24 are higher than for same reporting periods in previous seasons. The sharp increase in influenza notifications and notification rates in this reporting period (Figure 1) is likely to be due to increased testing for influenza associated with H1N1 Influenza 09.

    Figure 1: Number of laboratory-confirmed influenza notifications including H1N1 Influenza 09, NNDSS, 1 January 2009 to 12 June 2009, by jurisdiction and week of diagnosis



    Figure 1: Number of laboratory-confirmed influenza notifications including H1N1 Influenza 09, NNDSS, 1 January 2009 to 12 June 2009, by jurisdiction and week of diagnosis

    Source: NNDSS


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    H1N1 influenza 09 influenza in Australia

    National analysis of H1N1 influenza 09

    Source: NetEpi

    As of Tuesday 16 June 2009, there are 1,877 confirmed cases of H1N1 Influenza 09 in Australia. The majority (65%) of confirmed cases have been identified in Victoria (Table 1).

    Five hundred and ten new confirmed cases have been reported since the last Australian Influenza Surveillance Report was compiled on 11 June 2009. Of these, 124 were reported in Victoria and 386 across the other jurisdictions. Victoria moved to a ‘modified sustain’ phase on 3 June 2009 and began targeted clinical testing of suspect H1N1 Influenza 09 cases. Therefore suspected cases are no longer tested if they are considered to be part of a known cluster. This will result in a lesser proportion of infected people in Victoria being identified and reported as a confirmed case.

    Table 1: Number and rate of laboratory-confirmed H1N1 influenza 09 notifications, by jurisdiction

    State
    Cases Percentage of total H1N1 notifications Rate per 100,000
    ACT
    48
    2.6
    14.1
    NSW
    216
    11.6
    3.1
    NT
    32
    1.7
    14.9
    Qld
    157
    8.4
    3.8
    SA
    77
    4.1
    4.9
    Tas
    35
    1.9
    7.1
    Vic
    1,216
    65.3
    23.4
    WA
    82
    4.4
    3.9
    Aus
    1,863
    100%
    8.9

    Note: 14 confirmed cases do not have a State or Territory identifier.
    Source: NetEpi 16 June 2009



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    Figure 2: The temporal distribution of laboratory confirmed cases of H1N1 Influenza 09 reported in Australia, 26 April 2009 to 16 June 2009, by jurisdiction

    Figure 2: The temporal distribution of laboratory confirmed cases of H1N1 Influenza 09 reported in Australia, 26 April 2009 to 16 June 2009, by jurisdiction

    Source: NetEPI 16 June 2009

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    Age and sex distribution of Australian cases

    Of the 1,860 confirmed cases for which gender is known, 845 (45%) are female and 1,015 (55%) are male. The national gender distribution with each 10-year age group is presented in Figure 3.

    The number of confirmed cases has been greatest among younger people, with 1493 (80%) of all confirmed cases occurring in people under the age of 30 and 792 (42%) of all cases occurring in the 10–19 age group. The median age of confirmed cases is 16. Less than 5% of all cases have occurred in people under the age of five, and only 6% of all cases have occurred in people over the age of 60.

    Figure 3: The distribution of laboratory confirmed cases of H1N1 Influenza 09 reported in Australia, 26 April 2009 to 16 June 2009, by age group and sex

    Figure 3: The distribution of laboratory confirmed cases of H1N1 Influenza 09 reported in Australia, 26 April 2009 to 16 June 2009, by age group and sex

    Source: NetEpi

    The age distribution of cases in other regions of the world also appears skewed towards younger age groups. Of 409 cases reported in 21 European countries, 142 (35%) were aged between two and 20 years old, 195 (48%) were aged between 20 and 39 years old and 56 (14%) were aged between 40 and 59. The number of cases aged over 60 years old was 10 (2%).1

    Of 642 confirmed cases identified in the USA between 15 April and 5 May 2009, 60% were 18 years of age or younger and 40% were aged between 10 and 18 years of age.2

    Of the first 115 cases identified in China for whom age was known, 83 (72%) were less than 31 years old and 54 (47%) were less than 21 years old.3 The majority (87%) of these cases were ‘imported’, so this data may not reflect the age distribution of cases of secondary transmission within China.

    Of 361 cases identified in Japan of 1 June 2009, 287 (80%) were between 10 and 19 years of age.4

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    Hospitalisations

    Fifty confirmed cases of H1N1 Influenza 09 were hospitalised during the period 26 April 2009 to 16 June 2009. On 16 June 2009, 10 confirmed cases were in hospital, with 3 of these in intensive care units. Further data are available on 22 of the hospitalised cases. For these cases the age range is 2-77 years of age. The median age of the hospitalised cases is 36. This is higher than the median age of all confirmed cases (16) indicating that the more severe cases are in the older age groups. Of the 22 cases, 10 (45%) are female and 12 (55%) are males. The gender distribution for hospitalised cases is the same as for all confirmed cases.

    Risk factors

    Several risk factors for severe disease associated with H1N1 Influenza 09 infection are suggested by existing knowledge of seasonal influenza and an analysis of global hospitalisations due to H1N1 Influenza 09. These risk factors include the following:
  • Chronic heart disease
  • Chronic lung disease
  • Diabetes
  • Immunosuppression
  • Obesity
  • Pregnancy

    While people of the age of 65 are typically at greater risk of severe illness associated with seasonal influenza, the age distribution of all global cases of H1N1 Influenza 09, including hospitalised cases, appears to be skewed towards younger age groups.
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    Cases in Aboriginal and/or Torres Strait Islander people

    As of 16 June 2009, 14 confirmed cases were identified among Aboriginal and/or Torres Strait Islander peoples. Of these, 5 were reported in the Northern Territory, 2 in NSW, 2 in Queensland, 2 in Tasmania, 2 in Victoria, and 1 in Western Australia. No jurisdictions have reported community transmission among Indigenous communities.

    Outbreaks have been reported among the Indigenous people living in the Nunavut and Manitoba provinces of Canada. As of 15 June 2009, 310 confirmed cases had been reported from the two provinces. Local media reports suggest that Indigenous people are over-represented among severe (hospitalised) cases in Manitoba. http://www.pddnet.com/news-ap-hl-swine-flu-is-hitting-first-nations-in-manitoba--061509/

    Symtpoms

    The clinical spectrum of H1N1 Influenza 09 is still being defined by health services in affected countries. To date, available information suggests that the vast majority of confirmed cases of H1N1 Influenza 09 have been characterised by self-limiting, uncomplicated febrile respiratory illness and symptoms similar to those of seasonal influenza. Complications and severe disease requiring hospitalisation have been reported in a minority of cases and 163 deaths worldwide have been attributed to H1N1 Influenza 09. It should be noted that the criteria on which the WHO raised the pandemic alert to phase six is based on pattern of global transmission, rather than severity of illness.

    Schools

    As of Tuesday 16 June 2009, there were 17 Australian schools closed in order to minimize spread of H1N1 Influenza 09. These schools were in the ACT, NT, QLD, SA and WA.
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    Seasonal influenza in Australia

    SOURCE: NNDSS Note: This section EXCLUDES any notifications of H1N1 Influenza 09 that are identifiable in NNDSS

    Laboratory confirmed influenza

    There have been 3,611 cases of laboratory confirmed influenza diagnosed and reported to the National Notifiable Diseases Surveillance System (NNDSS) in 2009 (Figure 4). There were 977 laboratory confirmed influenza cases in the same period last year.
    Influenza notifications are above the 5 year rolling mean for this period (Figure 4). The sharp increase in influenza notifications and notification rates in this reporting period (Figure 4 and 5) is likely to be due to increased testing for influenza associated with H1N1 Influenza 09. Also, some jurisdictions do not enter subtyping data into NNDSS and it is therefore not possible to distinguish some notifications of H1N1 Influenza 09 from seasonal influenza.
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    Figure 4: Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 12 June 2009, by jurisdiction and week of diagnosis

    Figure 4: Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 12 June 2009, by jurisdiction and week of diagnosis

    Source: National Notifiable Diseases Surveillance System

    Notifications in 2009 have been predominantly from Victoria (1,283 notifications – 36%), Queensland (1,045 notifications – 29%), New South Wales (504 notifications – 14%), and South Australia (393 notifications – 11%). The Australian Capital Territory, Northern Territory, Tasmania and Western Australia accounted for the other 10% or 386 notifications (Table 2, Figure 5).
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    Table 2: Number and rate of laboratory-confirmed notifications by jurisdiction, NNDSS, 1 January 2009 to 12 June 2009, NNDSS

    State
    Cases Percentage of total notifications Rate per 100,000 Average rate YTD 2004-2008
    ACT
    59
    1.6%
    17.4
    19.8
    NSW
    504
    14.0%
    7.3
    15.5
    NT
    106
    2.9%
    49.3
    36.4
    Qld
    1045
    28.9%
    25.0
    24.4
    SA
    393
    10.9%
    24.8
    4.9
    Tas
    16
    0.4%
    3.2
    8.2
    Vic
    1283
    35.5%
    24.6
    6.6
    WA
    205
    5.7%
    9.7
    14.3
    Aus
    3,611
    100%
    17.2
    2.9


    Figure 5: Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 12 June 2009, by jurisdiction and week of diagnosis

    Figure 5: Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 12 June 2009, by jurisdiction and week of diagnosis

    Source: National Notifiable Diseases Surveillance System

    National age-specific notification rates year to date show the highest rates of notifications occurred in males aged 15-19 years, closely followed by both males and females aged 10-14 years (Figure 6).
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    Figure 6: Notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2009 to 12 June 2009, by age group and sex


    Figure 6: Notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2009 to 12 June 2009, by age group and sex

    Source: National Notifiable Diseases Surveillance System

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    Mapping of influenza notifications by statistical division of residence indicates that there are areas within states, with higher rates compared to the rest of the state or Australia (Figure 7). The numbers on the map indicate the number of cases occurring within each region.


    Figure 7. Map of notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2008 to 12 June 2009, by Statistical Division of residence

    Figure 7. Map of notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2008 to 12 June 2009, by Statistical Division of residence

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    Laboratory surveillance

    The Victorian Infectious Disease Reference Laboratory (VIDRL) has reported that in the fortnight ending 7 June 2009, picornavirus, RSV and Influenza A were the most commonly detected respiratory virus in Victoria (For full report see: www.vidrl.org.au).

    South Australia has reported that in the fortnight ending 7 June 2009, influenza A, rhinovirus, respiratory syncytial virus and adenovirus were the most commonly detected respiratory viruses in South Australia.

    Syndromic surveillance

    Sentinel general practice
    Data available from the Australian Sentinel Practices Research Network (ASPREN), the Northern Territory GP surveillance system, and VIDRL up until 7 June 2009 show that ILI consultation rates have increased during this reporting period (Figure 8). In the last week, the presentation rate to sentinel GPs in Australia was approximately 16 cases per 1,000 patients seen.

    As data from NT and VIDRL surveillance systems are being combined with ASPREN data, rates may not be readily comparable between 2007/2008 and 2009.

    Figure 8. Rate of ILI reported from GP ILI surveillance systems from 2007 to 2009 by week


    Figure 8. Rate of ILI reported from GP ILI surveillance systems from 2007 to 2009 by week
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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 have increased in recent weeks but continue to follow similar trends to recent years (Figure 9).

    Figure 9. Absenteeism rates, 1 January 2007 to 27 May 2009, by week and NNDSS influenza notifications, Rate per 100,000 population, 1 January 2009 to 29 May 2009, by week


    Figure 9. Absenteeism rates, 1 January 2007 to 27 May 2009, by week and NNDSS influenza notifications, Rate per 100,000 population, 1 January 2009 to 29 May 2009, by week

    Source: Absenteeism data


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    International

    New Zealand influenza activity

    The current rate of influenza in New Zealand is lower than at the same time last year (Figure 10).

    Figure 10. Weekly consultation rates for ILI in New Zealand, 2007, 2008 and 2009

    Figure 10. Weekly consultation rates for ILI in New Zealand, 2007, 2008 and 2009


    SOURCE: New Zealand Influenza Weekly Update

    For further information please contact: flu@health.gov.au

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    Data considerations

    NetEPI (Web based outbreak case reporting system)

    All jurisdictions are reporting H1N1 Influenza 09 cases using NetEPI. Data included in this report were extracted and analysed on 16 June 2009.

    Figures and Tables are based on data extracted from NetEPI, a web-based outbreak case reporting symptom used by all jurisdictions, and based on onset date where available. Where an onset date is not available in NetEPI 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.

    NNSSS (National Notifiable Diseases Surveillance System)

    NNDSS comprises of notifications from jurisdictions of laboratory-confirmed influenza cases. Influenza is notifiable in all jurisdictions in Australia. Data included in this report were extracted and analysed on 16 June 2009.

    Laboratory Surveillance data

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

    GP Surveillance

    ASPREN, the Australian Sentinel Practices Research Network, has Sentinel GPs who report 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, and are currently available up until 7 June 2009.

    Northern Territory GP surveillance data are sent to the Surveillance Branch on a weekly basis, and are currently available up to 7 June 2009.

    VIDRL influenza surveillance data are sent to the Surveillance Branch on a weekly basis, and are currently available up to 7 June 2009.

    Absenteeism Surveillance

    Absenteeism data are provided weekly to the Surveillance Branch by a national employer and are currently available up until 27 May 2009.
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    References

    1. ECDC SURVEILLANCE REPORT: Preliminary report on case-based analysis of influenza A(H1N1) in EU and EEA/EFTA countries, 6 June 2009
    2. New England Journal of Medicine 360;25, 18 June 2009
    3. ProMED/AH/EDR> Influenza A (H1N1) - worldwide (64), 16 June 2009
    3. Nishiura H, Castillo-Chavez C, Safan M, Chowell G. Transmission potential of the new influenza A(H1N1) virus and its age-specificity in Japan. Euro Surveill 2009;14(22):pii=19227. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19227