Australian influenza report 2009 - 23 May to 5 June 2009 (#5/09)

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. 5
Week ending 5 June 2009

A print friendly version of this report is available as a PDF (92 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 11 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 the increased testing for H1N1 Influenza 09.
  • Notifications of H1N1 Influenza 09 continue to rise, with 75% of cases notified in Victoria - particularly in the Northern and Western suburbs of Melbourne.
  • 55% of H1N1 Influenza 09 cases in Australia and 63% of cases in Victoria to date have been in school aged children (5 – 17 years), with a median age of 16 years in Australia.
  • Six cases of H1N1 Influenza 09 have been reported in Aboriginal and/or Torres Strait Islander people.
  • Syndromic and laboratory surveillance indicates that ILI in the community has started to rise. Laboratory reports indicate that to 5 July the influenza season has not yet commenced in Australia.
  • Seasonal influenza notifications rates continue to be highest in children less than one year of age.
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Laboratory confirmed influenza

Influenza A is the predominant circulating type in Australia. YTD, 2,214 cases (89%) of influenza notifications to NNDSS have been influenza type A, 184 cases (7%) have been influenza type B and 90 cases (4%) were untyped (Figure 1).

Figure 1: Typing characteristics of notifications of laboratory-confirmed influenza, Australia, 1 January 2009 to 5 June 2009, week of diagnosis, NNDSS



Figure 1: Typing characteristics of notifications of laboratory-confirmed influenza, Australia, 1 January 2009 to 5 June 2009, week of diagnosis, NNDSS

Source: NNDSS


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H1N1 influenza 09 influenza in Australia

Since the outbreak of H1N1 Influenza 09 was first identified, there have been 1380 confirmed cases identified in Australia (as of 11 June, 2009). This rapid increase reflects the rise in the number of confirmed cases with infection acquired in Australia. As Table 1 below demonstrates, the bulk of these cases (80% of confirmed cases) were from Victoria. As of early June new cases in Victoria will not be subject to laboratory testing if they are part of an existing cluster. This decision will result in a decrease in the number of cases reported and the epidemic curve should be interpreted with this in mind.

Please note that the following 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 following figures are based.

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
9
0.7%
2.6
NSW
116
8.5%
1.7
NT
7
0.5%
3.3
Qld
71
5.2%
1.7
SA
20
1.5%
1.3
Tas
15
1.1%
3.0
Vic
1092
79.9%
21.0
WA
37
2.7%
1.8
Aus
1,367
100%
6.5

Note: 13 confirmed cases do not have a state or territory identifier.
Source: NetEpi 16 June 2009



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Figure 2: Number of laboratory-confirmed H1N1 Influenza 09 notifications, NetEpi, 26 April 2009 to 11 June 2009, by jurisdiction and date of onset, notification or detection

Figure 2: Number of laboratory-confirmed H1N1 Influenza 09 notifications, NetEpi, 26 April 2009 to 11 June 2009, by jurisdiction and date of onset, notification or detection

Source: NetEPI

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The median age of Australian cases is 16 years. The disease is predominantly affecting younger people with 29.1% of cases being aged 13 – 17 years and a further 25.9% of cases being aged 5 – 12 years (Figure 3).

There are more males than females among confirmed cases. Forty-five per cent (n=623) of cases are female and fifty five percent (n=752) of cases are male. Figure 3 shows the higher proportion of males in all age groups except those aged 25-49 years of age. This distribution may reflect the opportunity for the virus to spread with, for example, outbreaks occurring amongst members of single sex sporting teams and single sex schools in Cairns and Perth.

Indigenous status was complete for 122 of 872 cases, of which 6 were reported as Aboriginal and/or Torres Strait Islander people.

Figure 3: Notification rates of laboratory-confirmed H1N1 Influenza 09, Australia, to 11 June 2009, by age group and sex

Figure 3: Notification rates of laboratory-confirmed H1N1 Influenza 09, Australia, to 11 June 2009, by age group and sex

Source: NetEpi


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Seasonal influenza in Australia

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

Laboratory confirmed influenza

There have been 2,488 cases of laboratory confirmed influenza diagnosed year-to-date (YTD) in 2009 (Figure 4). There were 917 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 (Figures 4 and 5) is likely to be due to increased testing for influenza associated with H1N1 Influenza 09.
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Figure 4: Number of laboratory-confirmed influenza notifications, NNDSS, 1 January 2009 to 5 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 Queensland (643 notifications – 27%), Victoria (617 notifications – 26%), New South Wales (446 notifications – 19%), and South Australia (342 notifications – 15%). The Australian Capital Territory, Northern Territory, Tasmania and Western Australia accounted for the other 13% or 305 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 5 June 2009, NNDSS

State
Cases Percentage of total notifications Rate per 100,000 Average rate YTD 2004-2008
ACT
41
1.7%
12.1
18.9
NSW
446
19.0%
6.5
14.7
NT
83
3.5%
38.6
35.5
Qld
643
27.3%
15.4
22.7
SA
342
14.5%
21.6
4.4
Tas
15
0.6%
3.0
7.8
Vic
617
26.2%
11.9
5.5
WA
166
7.1%
7.9
13.3
Aus
2353
100%
11.2
2.6


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

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

Source: National Notifiable Diseases Surveillance System

National age-specific notification rates YTD show the highest rates of notifications occurred in females aged 10-14 and 20-24 years, followed by males aged 0-19 years old (Figure 6).
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Figure 6: Notification rates of laboratory-confirmed influenza, Australia, 1 January 2009 to 5 June 2009, by age group and sex


Figure 6: Notification rates of laboratory-confirmed influenza, Australia, 1 January 2009 to 5 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 5 June 2009, by Statistical Division of residence

Figure 7. Map of notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2008 to 5 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 viruses in Victoria (For full report see: www.vidrl.org.au).

South Australia have reported that in the fortnight ending 31 May 2009, picornavirus, adenovirus and Influenza A 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 17 cases per 1000 patients seen. This may be related to an increase in the number of people visiting their GPs with ILI as a result of the large amount of media around H1N1 Influenza 09.

As data from NT and VIDRL surveillance systems have been 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 and may indicate that seasonal influenza is not yet widespread in the community (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 10 June 2009.

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 11 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.