Australian influenza report 2011 - 20 August to 2 September 2011 (#12/11)

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. A more in-depth annual report is also published in Communicable Diseases Intelligence.

Page last updated: September 2011

Report No.12
Week ending 2 September 2011

A print friendly version of this report is available as a PDF (275 KB)

The Department of Health and Ageing acknowledges the providers of the many sources of data used in this report and greatly appreciates their contribution.

Key Indicators

Influenza activity and severity in the community is monitored using the following indicators and surveillance systems:

Is the situation changing?Indicated by trends in:
  • laboratory confirmed cases reported to the National Notifiable Diseases Surveillance System;
  • GP Sentinel influenza-like illness (ILI) Surveillance;
  • emergency department (ED) presentations for ILI;
  • ILI-related absenteeism and call centre calls: and
  • sentinel laboratory test results.
How severe is the disease, and is severity changing?Indicated by trends in:
  • hospitalisations, ICU admissions and deaths from sentinel systems; and
  • clinical severity in hospitalised cases and ICU admissions.
Is the virus changing?Indicated by trends in:
  • drug resistance; and
  • genetic drift or shift from laboratory surveillance.

Summary

  • Levels of influenza-like illness (ILI) in the community continued to increase through both sentinel general practitioner surveillance systems and ILI presentations to emergency departments.
  • Notifications have continued to decrease in Queensland and New South Wales and recently have also started to decrease in other states and territories, except the Northern Territory. Currently the weekly number of notifications in the ACT, New South Wales, Queensland and Tasmania remain above the peak frequency of notifications observed in 2010.
  • During this fortnights reporting period there were 2,589 laboratory confirmed notifications of influenza, with Queensland reporting the highest number of notifications, followed by South Australia. Nationally, the majority of virus detections have been pandemic (H1N1) 2009, with co-circulation of influenza B.
  • The majority of states and territories have predominately reported pandemic (H1N1) 2009, with co-circulation of influenza B. However in Tasmania and New South Wales influenza B is the dominant strain, and in Western Australia, where mostly pandemic (H1N1) 2009 is reported, almost a quarter of reports are A/H3N2 and there is very little influenza B.
  • As at 2 September 2011, there have been 19,987 confirmed cases of influenza reported to the National Notifiable Diseases Surveillance System (NNDSS) in 2011. Nationally weekly notifications for this season have peaked. This season’s peak appears to have occurred in the week ending 5 August 2011 with 1,952 influenza notifications, and was above the peak frequency experienced in previous years, except 2009.
  • In addition to the previously reported cluster of pandemic (H1N1) 2009 influenza viruses showing resistance to oseltamivir within the Hunter New England region of New South Wales, a further two cases linked to this cluster have been detected in other regions of NSW. These additional cases had no prior travel history to the Hunter New England region. All of the viruses are sensitive to zanamivir and have not shown any antigenic changes that would affect their recognition by vaccine-induced antibodies.
  • The WHO has reported that influenza activity in the temperate regions of the northern hemisphere remains low. Influenza transmission continues to occur in a few countries of the tropical region. After peaking in early June, influenza transmission in South Africa has declined to low levels. In New Zealand, rates of national ILI consultations are now above baseline activity levels and influenza type B is currently the predominant strain circulating.
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1. Influenza activity in Australia

Influenza-Like Illness

Sentinel General Practice Surveillance

Sentinel general practitioner ILI consultation rates have remained relatively stable in recent weeks. In the week ending 28 August 2011, the national ILI consultation rate to sentinel GPs was 16 cases per 1,000 consultations, a similar consultation rate to the previous fortnight (Figure 1).

Figure 1. Weekly rate of ILI reported from GP ILI surveillance systems from 1 January 2008 to 28 August 2011*
Figure 1. 	Weekly rate of ILI reported from GP ILI surveillance systems from 1 January 2008 to 28 August 2011

* Delays in the reporting of data may cause data to change retrospectively. As data from the VIDRL surveillance system is combined with ASPREN data for 2010 and 2011, rates may not be directly comparable across 2008 and 2009.
SOURCE: ASPREN and VIDRL GP surveillance system1.


In the fortnight ending 28 August 2011, specimens were collected from half of ASPREN ILI patients. Of these patients, 58 specimens (32%) were positive for influenza, which is a decrease from the proportion that were positive in the previous fortnight. Twenty-six specimens were typed as influenza type A, and were mostly pandemic (H1N1) 2009; and the remainder (32) were influenza type B. Forty-five specimens were positive for other respiratory viruses, with the majority of these being rhinovirus (15) (Table 1).

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Table 1. ASPREN ILI consultations laboratory respiratory viral tests that were positive for influenza or other respiratory virus, 1 January 2011 to 28 August 2011.
        ASPREN Fortnight
        (15-28 August 2011)
        ASPREN YTD
        (1 Jan – 28 August 2011)
Total specimens tested
180
1245
Total Influenza Positive
58
346
Influenza A
26
225
Pandemic (H1N1) 2009
16
177
Seasonal A/H3N2
5
19
Influenza A untyped
5
29
Influenza B
32
121
Total Positive other Resp. Viruses*
45
339

* Other respiratory viruses include RSV, para-influenza, adenovirus and rhinovirus.


Western Australia Emergency Departments

In the fortnight ending 4 September 2011, respiratory viral presentations to WA EDs increased, and presentations remain well above baseline levels. Over this period there were 1,279 presentations, including 104 admissions (Figure 2). The proportion of presentations admitted to hospital over this period remained stable and represented 8% of presentations.

Figure 2. Number of respiratory viral presentations to WA EDs from 1 January 2008 to 4 September 2011, by week
Figure 2. Number of respiratory viral presentations to WA EDs from 1 January 2008 to 4 September 2011, by week

Source: WA ‘Virus Watch’ Report2


New South Wales Emergency Departments

In the week ending 2 September 2011 the number of patients presenting to NSW EDs with ILI decreased and remained within the usual range for this time of year. Just over half of ILI presentations were reported in people aged 15 to 34 years (51%). Total admissions to critical care units for ILI and pneumonia increased slightly this week, and remained within the usual range for this time of year. 3

FluTracking

FluTracking, a national online system for collecting data on ILI in the community, noted that in the week ending 4 September 2011 fever and cough was reported by 2.9% of vaccinated participants and 3.3% of unvaccinated participants. 4 Fever, cough and absence from normal duties was reported by 1.6% of vaccinated participants and 1.6% of unvaccinated participants. Rates of ILI among FluTracking participants has remained relatively stable this season, compared to previous years (Figure 3).

Up to 4 September 2011, 5,680 out of 10,186 (55.8%) participants reported having received the seasonal vaccine so far. Of the 2,324 participants who identified as working face-to-face with patients, 1,699 (73.1%) have received the vaccine.

Figure 3. Rate of fever and cough among FluTracking participants by week, between May and October, 2007 to 2011.
Figure 3.  Rate of fever and cough among FluTracking participants by week, between May and October, 2007 to 2011

Source: FluTracking


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National Health Call Centre Network

The number of ILI-related calls to the National Health Call Centre Network (NHCCN) remained relatively stable compared to the previous fortnight. The percentage of total calls also remained relatively stable. In the week ending 4 September 2011 9% of calls to the NHCCN were ILI related, which is slightly above the same period in 2010 (Figure 4).

Figure 4. Number of calls to the NHCCN related to ILI and percentage of total calls, Australia, 1 January 2010 to 4 September 2011
Figure 4.  Number of calls to the NHCCN related to ILI and percentage of total calls, Australia, 1 January 2010 to 4 September 2011

Note: National data do not include QLD and VIC
Source: NHCCN data


Laboratory Confirmed Influenza

Laboratory Confirmed Cases Notified to Health Departments

During this reporting period there were 2,589 laboratory confirmed influenza notifications reported to the NNDSS. Of these notifications, there were 1,081 in Qld, 476 in SA, 368 in Vic, 338 in NSW, 219 in WA, 49 in the NT, 36 in TAS, and 22 in the ACT (Figure 5). A weekly breakdown of trends by state and territory highlights that notifications have continued to be highest in Queensland and South Australia, with New South Wales also still high. Among these states however, notifications are decreasing or have plateaued following recent peaks. In the other states and territories, notifications are also starting to decrease, except in the Northern Territory. The weekly number of influenza notifications currently being reported in the ACT, New South Wales, Queensland and Tasmania are higher than the peak frequency experienced in 2010 (Figure 7).

Figure 5. Laboratory confirmed cases of influenza in Australia, 1 January to 2 September 2011, by state, by week.
Figure 5. Laboratory confirmed cases of influenza in Australia, 1 January to 2 September 2011, by state, by week

Source: NNDSS 2011


Up to 2 September, there have been 19,987 laboratory confirmed notifications of influenza diagnosed during 2011 (Figure 6). Of these notifications, there have been 8,749 notified in Qld, 4,219 in NSW, 3,324 in SA, 1,805 in Vic, 998 in WA, 422 in the NT, 257 in Tas and 213 in the ACT. Nationally weekly notifications for this season have peaked. This season’s peak appears to have occurred in the week ending 5 August 2011 with 1,952 influenza notifications, and was above the peak frequency experienced in previous years, except 2009. Over the summer months, all jurisdictions reported higher than usual numbers of notifications, especially in the Northern Territory and Queensland. The reason for this unusually high activity is not clear, but it does not appear to be due solely to increased testing.

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Figure 6. Laboratory confirmed cases of influenza in Australia, 1 January 2005 to 2 September 2011
Figure 6. Laboratory confirmed cases of influenza in Australia, 1 January 2005 to 2 September 2011
Source: NNDSS 2011
Figure 7. State breakdowns of laboratory confirmed cases of influenza, 1 January to 2 September 2011, by week
Figure 7.  State breakdowns of laboratory confirmed cases of influenza, 1 January to 2 September 2011, by week: ACT
Figure 7.  State breakdowns of laboratory confirmed cases of influenza, 1 January to 2 September 2011, by week: NSW
Figure 7.  State breakdowns of laboratory confirmed cases of influenza, 1 January to 2 September 2011, by week: NT
Figure 7.  State breakdowns of laboratory confirmed cases of influenza, 1 January to 2 September 2011, by week: QLD
Figure 7.  State breakdowns of laboratory confirmed cases of influenza, 1 January to 2 September 2011, by week:SA
Figure 7.  State breakdowns of laboratory confirmed cases of influenza, 1 January to 2 September 2011, by week: TAS
Figure 7.  State breakdowns of laboratory confirmed cases of influenza, 1 January to 2 September 2011, by week: VIC
Figure 7.  State breakdowns of laboratory confirmed cases of influenza, 1 January to 2 September 2011, by week: WA

Source: NNDSS 2011


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Of the 2,589 influenza notifications reported to the NNDSS this reporting period, 1,684 were influenza A (1,149 were influenza A (untyped), 459 were pandemic (H1N1) 2009 and 76 were A/H3N2), 896 were influenza B, 3 were influenza A&B and 6 notifications were reported as untyped (Figure 8). Compared to the beginning of the year, there appears to be very little A/H3N2 circulating.

The majority of states and territories have reported mostly pandemic (H1N1) 2009, with co-circulation of influenza B. However, in Tasmania and more recently New South Wales, influenza B is the dominant strain, and in Western Australia there is very little influenza B circulating and of the small number of A/H3N2 notifications nationally these are also mostly from Western Australia.

So far in 2011, 14,222 (71%) cases were reported as influenza A (35% influenza A (untyped), 31% pandemic (H1N1) 2009 and 5% A/H3N2) and 5,620 (28%) were influenza B. A further 59 (<1%) were influenza type A&B and 86 (<1%) were untyped (Figure 8).

Note: Northern Territory sub-typing results reported to the NNDSS as "Influenza A/Not Pandemic" have been counted as influenza A/H3N2 notifications.

Figure 8. Laboratory confirmed cases of influenza in Australia, 1 January 2011 to 2 September 2011, by sub-type and week
Figure 8. Laboratory confirmed cases of influenza in Australia, 1 January 2011 to 2 September 2011, by sub-type and week

Source: NNDSS 2011


Sentinel Laboratory Surveillance

Results from sentinel laboratory surveillance systems for this reporting period show that 15.6% (274/1,759) of the respiratory viral tests conducted over this period were positive for influenza (Table 2). Positive influenza specimens were reported from all sentinel laboratories.

Table 2. Sentinel laboratory respiratory virus testing results, 23 July to 2 September 2011
NSW NICWA NICNT
(Reported by WA NIC)
VIC NICTAS
PCR Testing Data
Total specimens tested4189092302128
Total Influenza Positive1216816825
Positive Influenza A514813610
Pandemic (H1N1) 20090980143
A/H3N24491212
Influenza A untyped11015
Positive Influenza B72003215
The most common respiratory virus detectedRhinovirus & RSVInfluenza A-Influenza A-
In 2011 a total of 10.6% of specimens have been positive for influenza. A breakdown of subtypes within this positive proportion by fortnight is highlighted in Figure 9.

Figure 9. Proportion of sentinel laboratory* tests positive for influenza, by subtype and fortnight, 30 April to 2 September 2011.
Figure 9.  Proportion of sentinel laboratory* tests positive for influenza, by subtype and fortnight, 30 April to 2 September 201

* Tasmanian PCR testing data included from 9 July 2011


Influenza Hospitalisations

Influenza Complications Alert Network (FluCAN) – Victoria and the Australian Capital Territory

The Influenza Complications Alert Network (FluCAN) sentinel hospital system in Victoria, South Australia, Western Australia and the ACT has reported 118 hospitalisations, including 13 ICU admissions, associated with influenza since 1 May 2011 (Figure 10). Over half (56%) of the hospitalisations and 77% of ICU admissions have been associated with pandemic (H1N1) 2009 infection. The mean age of patients hospitalised has been 46.6 years.

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Figure 10. Number of influenza hospitalisations at sentinel hospitals, Victoria, South Australia, Western Australia and the ACT, by week and influenza subtype, 1 May to 1 September 2011
Figure 10.  Number of influenza hospitalisations at sentinel hospitals, Victoria, South Australia, Western Australia and the ACT, by week and influenza subtype, 1 May to 1 September 2011

Source: FluCAN Sentinel Hospitals


Australian Paediatric Surveillance

The Australian Paediatric Surveillance Unit (APSU) conducts seasonal surveillance of children aged 15 years and under who are hospitalised with severe complications of influenza. Between 1 July and 6 September 2011, there have been 39 hospitalisations associated with severe influenza complications in children, including 17 ICU admissions. The majority of these hospitalisations were associated with pandemic (H1N1) 2009 infection. Of the 29 hospitalisations with completed questionnaires, 11 were noted as having underlying chronic medical conditions.

Deaths associated with influenza and pneumonia

Nationally Notified Influenza Associated Deaths

In 2011, 11 influenza associated deaths have been notified to the NNDSS, with a median age of 45 years. Eight of these cases were reported as having a pandemic (H1N1) 2009 infection, two with influenza type B and the other case reported as having influenza type A (untyped).

New South Wales Influenza and Pneumonia Death Registrations

Death registration data up to 19 August 2011 showed that there were 1.2 pneumonia or influenza associated deaths per 100,000 population in NSW, which is below the seasonal threshold of 1.8 per 100,000 NSW population for this period (Figure 11).3

Figure 11. Rate of deaths classified as influenza and pneumonia from the NSW Registered Death Certificates, 2006 to 19 August 2011
Figure 11.  Rate of deaths classified as influenza and pneumonia from the NSW Registered Death Certificates, 2006 to 19 August 2011
Source: NSW ‘Influenza Weekly Epidemiology Report’3
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2. Virology

Typing and antigenic characterisation

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

From 1 January to 4 September 2011, there were 1,695 Australian influenza isolates subtyped by the WHO CC with half of these isolates subtyped as pandemic (H1N1) 2009 (Table 3).

Table 3. Typing of influenza isolates from the WHO Collaborating Centre, from 1 January 2011 to 4 September 2011
Type/SubtypeACTNSWNTQLDSATASVICWATOTAL
Pandemic (H1N1) 2009
9
317
31
308
53
22
83
27
850
A(H3N2)
1
17
48
137
13
6
32
10
264
B
1
109
37
105
211
9
104
5
581
Total
11
443
116
550
277
37
219
42
1695

SOURCE: WHO CC
Please note: There may be up to a month delay on reporting of samples.
Isolates tested by the WHO CC are not necessarily a random sample of all those in the community.


Antigenic characterisation has shown influenza isolates to be a close match with the composition of the 2011 southern hemisphere influenza vaccine with some viruses showing reduced reactivity, however there has been insufficient testing to date to determine any general trends.

Antiviral Resistance

The WHO Collaborating Centre in Melbourne has reported that from 1 January to 11 September 2011, 15 influenza viral isolates (out of 1,649 tested) have shown resistance to the neuraminidase inhibitor oseltamivir by enzyme inhibition assay (EIA). A further 18 specimens, out of a total of 203 tested by pyrosequencing, have shown the H275Y mutation known to confer resistance to oseltamivir. A total of 33 influenza viruses have shown resistance to oseltamivir in 2011, all have been the pandemic (H1N1) 2009 subtype.

The recent increases in oseltamivir resistance in pandemic (H1N1) 2009 influenza isolates have predominately occurred in the Hunter New England region of New South Wales between June and August 2011. The cluster consists of 25 cases, of which 6 were hospitalised and three were pregnant. A further two oseltamivir-resistant pandemic (H1N1) 2009 viruses, sampled in July and August, have also been found to belong to the cluster. Both of these cases were detected outside the Hunter New England region with no recent travel history to this region. None of the cases reported so far were treated with oseltamivir prior to their positive test for influenza. All of the viruses are sensitive to zanamivir and have not shown any antigenic changes that would affect their recognition by vaccine-induced antibodies.

3. International Influenza Surveillance

The WHO5 has reported that as at 26 August 2011 influenza activity in the temperate regions of the northern hemisphere remains low or undetectable. In the tropical zone, influenza activity is mostly reported as low, with some ongoing transmission reported in countries of the Americas (Dominican Republic, Cuba, Honduras and Brazil); western Africa (Ghana, Cameroon and Senegal); and southern Asia (India, Bangladesh, Thailand and Singapore). In South America, the influenza season has been reported as being very mild with variation in the predominant type and subtype of viruses circulating in different countries of the area. Influenza activity in South Africa is continuing at low levels, after peaking in early to mid June. Viral transmission within South Africa was dominated by pandemic A (H1N1) 2009, with smaller numbers of influenza type B.

In New Zealand6, for the week ending 4 September 2011, the national rate of ILI consultations are now above the baseline activity levels with 13 of the twenty district health boards above the national average weekly consultation rate. Influenza type B continues to be the predominant strain.

National Influenza Centres in 70 countries have reported that for the period 31 July to 13 August 2011, a total of 923 specimens were reported as positive for influenza viruses, 660 (72%) were typed as influenza A and 263 (28%) as influenza B. Of the sub-typed influenza A viruses reported, 52% were pandemic (H1N1)2009 and 48% were influenza A(H3N2) 7.

WHO have released a summary review of the northern hemisphere winter influenza season8. The summary review notes that the most commonly detected virus was different in North America, where influenza A(H3N2) and influenza type B co-circulated with pandemic (H1N1) 2009, and Europe, where influenza A(H1N1)2009 was by far the most commonly detected virus. Although it was no longer the predominant influenza virus circulating in many parts of the world, pandemic (H1N1) 2009 otherwise behaved much the same way as it had during the pandemic in terms of the age groups most affected and the clinical pattern of illness. More than 90% of viruses detected around the world during the northern hemisphere influenza season were similar antigenically to those found in the seasonal trivalent influenza vaccine. Antiviral resistance in pandemic (H1N1)2009 remained at a very low level.

The WHO has released their recommendation for the antigen composition of 2011-2012 northern hemisphere influenza season trivalent flu vaccine9. It is recommended that vaccines contain the following:
  • an A/California/7/2009 (H1N1)-like virus;
  • an A/Perth/16/2009 (H3N2)-like virus;
  • a B/Brisbane/60/2008-like virus.
This recommended composition is the same as the 2010-2011 Northern Hemisphere and the 2011 Southern Hemisphere vaccine compositions.

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4. 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 as the season progresses, this report will be updated with the additional information.

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. 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 Surveillance Team through flu@health.gov.au.

Sentinel General Practice Surveillance

The Australian Sentinel Practices Research Network (ASPREN) has Sentinel GPs who report ILI presentation rates in NSW, NT, 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 2011 may be different from that of previous years. ASPREN data and VIDRL influenza surveillance data are sent to the Department on a weekly basis. Approximately 30% of all ILI patients presenting to ASPREN sentinel GPs are swabbed for laboratory testing. Please note the results of ASPREN ILI laboratory respiratory viral tests now include Western Australia.

Further information on Sentinel GPs’ Influenza Surveillance and ASPREN activities are available at www.dmac.adelaide.edu.au/aspren.

Sentinel Emergency Department 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 eight Perth EDs.

NSW - ED surveillance data are extracted from the ‘Weekly Influenza Report, NSW’. The New South Wales Influenza Surveillance Program collects data from 56 EDs across New South Wales.

FluTracking

FluTracking is a project of the University of Newcastle, the Hunter New England Area Health Service and the Hunter Medical Research Institute. FluTracking is an online health surveillance system to detect epidemics of influenza. It involves participants from around Australia completing a simple online weekly survey, which collects data on the rate of ILI symptoms in communities.
Further information on FluTracking is available at www.flutracking.net/index.html.

National Notifiable Diseases Surveillance System (NNDSS)

Laboratory confirmed influenza (all types) is notifiable under public health legislation in all jurisdictions in Australia. Confirmed cases of influenza are notified through the NNDSS by all jurisdictions. The national case definition is available at: http://www.health.gov.au/internet/main/publishing.nsf/Content/cda-surveil-nndss-casedefs-cd_flu.htm.

Analyses of Australian cases are based on the diagnosis date, which is the earliest of the onset date, specimen date or notification date.

Sentinel Laboratory Surveillance data

Laboratory testing data are provided weekly directly from PathWest (WA), VIDRL (VIC), ICPMR (NSW), Tasmanian laboratories reporting PCR results, and ASPREN (national).

Influenza Complications Alert Network (FluCAN)

The Influenza Complications Alert Network (FluCAN) sentinel hospital system monitors influenza hospitalisations at the following sites:
  • Victoria – Geelong Hospital, Royal Melbourne Hospital, Monash Medical Centre and Alfred Hospital;
  • Australian Capital Territory – Canberra Hospital and Calvary Hospital;
  • South Australia – Royal Adelaide Hospital;
  • Western Australia – Royal Perth Hospital.
  • Influenza counts are based on active surveillance at each site for admissions with PCR-confirmed influenza in adults. Some adjustments may be made in previous periods as test results become available. ICU status is as determined at the time of admission and does not include patients subsequently transferred to ICU.

Australian Paediatric Surveillance Unit

The Australian Paediatric Surveillance Unit (APSU) conducts seasonal surveillance of children aged 15 years and under who are hospitalised with severe complications of influenza. Reports are collated on a weekly basis from approximately 1,300 paediatricians and other child health clinicians around Australia. The protocol and case definition is available at:
http://www.apsu.org.au/download.cfm?DownloadFile=96DE7B48-0CC2-E99A-525BCD4BD6A2CB80.

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

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

Deaths associated with influenza and pneumonia

Nationally reported influenza associated deaths are notified by jurisdictions to the NNDSS which is maintained by the Department of Health and Ageing. However these are an underestimation of the true number of deaths occurring in the community associated with influenza.

NSW influenza and pneumonia deaths data are collected from the NSW Registry of Births, Deaths and Marriages. Figure 12 is extracted from the ‘Weekly Influenza Report, NSW’. NSW Registered Death Certificates are routinely reviewed for deaths attributed to pneumonia or influenza. While pneumonia has many causes, a well-known indicator of seasonal and pandemic influenza activity is an increase in the number of death certificates that mention pneumonia or influenza as a cause of death. The predicted seasonal baseline estimates the predicted rate of influenza or pneumonia deaths in the absence of influenza epidemics. If deaths exceed the epidemic threshold, then it may be an indication that influenza is beginning to circulate widely.

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5. References

1 The 2011 Victorian Influenza Vaccine Effectiveness Audit Report #17, 28 August 2011. Available from: www.victorianflusurveillance.com.au. Accessed 9 September 2011.
2 WA Virus Watch Report, 4 September 2011. Available from: http://www.public.health.wa.gov.au/3/487/3/virus_watch.pm. Accessed 9 September 2011
3 NSW Influenza Weekly Epidemiology Report, 27 August to 2 September 2011. Available from: http://www.health.nsw.gov.au/resources/publichealth/infectious/influenza/pdf/week_ending_02092011.pdf, Accessed 9 September 2011.
4 Flutracking Weekly Interim Report #18, 4 September 2011. Available from: http://www1.hnehealth.nsw.gov.au/hneph/HNEPHApplications/FluSurvey/Reports/LatestReport.pdf. Accessed 9 September 2011.
5 WHO Weekly Influenza Update 141 (26 August 2011). Available from: http://www.who.int/csr/disease/influenza/latest_update_GIP_surveillance/en/index.html#. Accessed 9 September 2011.
6 New Zealand Influenza Weekly Update, Week Ending 4 September 2011. Available from: http://www.surv.esr.cri.nz/virology/influenza_weekly_update.php, Accessed 9 September 2011.
7 WHO Laboratory confirmed data from the Global Influenza Surveillance Network – 26 August 2011. Available from: http://www.who.int/csr/disease/influenza/influenzanetwork/flunet/summaryreport/en/index.html. Accessed 9 September 2011.
8 WHO Summary review of the 2010-2011 northern hemisphere winter influenza season. Available from: http://www.who.int/csr/disease/influenza/2010_2011_GIP_surveillance_seasonal_review/en/index.html. Accessed 16 June 2011.
9 WHO Recommended composition of influenza virus vaccines for use in the 2011-2012 northern hemisphere influenza season. Available from: http://www.who.int/csr/disease/influenza/recommendations_2011_12north/en/index.html. Accessed 3 June 2011.