Australian influenza report 2011 - 16to 29 April 2011 (#3/11)

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: 10 May 2011

Report No. 3
Week ending 16 to 29 April 2011

A print friendly version of this report is available as a PDF (208 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.
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Summary

Levels of influenza-like illness (ILI) in the community have increased slightly compared to recent weeks, however they continue to remain low through the majority of ILI surveillance systems this reporting period.
All jurisdictions have been reporting higher than usual numbers of laboratory confirmed influenza notifications over the summer months, however in recent weeks there has been a decline in the number of notifications in most jurisdictions.

During this reporting period there were 175 laboratory confirmed notifications of influenza, which included 103 cases of influenza A untyped, 31 cases of pandemic (H1N1) 2009, 3 of A/H3N2 and 37 cases of influenza B. Queensland reported the highest number of notifications.

As at 29 April 2011, there have been 3,141 confirmed cases of influenza reported to the National Notifiable Diseases Surveillance System (NNDSS) in 2011, compared with 651 for the same period in 2010.

The WHO has reported that influenza activity in the Northern Hemisphere has returned to baseline levels in most areas, indicating the season is now ending.

1. Influenza activity in Australia

Influenza-Like Illness

Sentinel General Practice Surveillance
In the week ending 24 April 2011, the national ILI consultation rate to sentinel GPs was 8.3 cases per 1,000 consultations, which is a slight increase from the previous week (Figure 1). The overall trend in ILI rates for 2011 are similar to those reported in 2008 to 2010.

Figure 1. Weekly rate of ILI reported from GP ILI surveillance systems from 1 January 2008 to 24 April 2011*

Figure 1. 	Weekly rate of ILI reported from GP ILI surveillance systems from 1 January 2008 to  24 April 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, rates may not be directly comparable across 2007, 2008 and 2009.
SOURCE: ASPREN and VIDRL GP surveillance system.


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Of the ASPREN ILI specimens collected in the fortnight ending 22 April 2011, 4 specimens (18%) were positive for influenza with 2 of those being positive for pandemic (H1N1) 2009 and 2 for influenza B. This is an increase in influenza positivity from the previous fortnight’s report where 8% were positive, however due to the small number of specimens tested it is difficult to determine any general trends. Twelve specimens were positive for other respiratory viruses, with the majority of those being rhinovirus (4) (Table 1). Please note the results of ASPREN ILI laboratory respiratory viral tests do not currently include Western Australia.

Table 1. ASPREN ILI consultations laboratory respiratory viral tests that were positive for influenza or other respiratory virus, 1 January 2011 to 22 April 2011

  ASPREN
(Fortnight 9 April –
22 April 2011)
ASPREN
(YTD 1 Jan – 8 April 2011)
Total specimens tested
22
162
Total Influenza Positive
4
25
   Influenza A
2
22
      Pandemic (H1N1) 2009
2
17
     Seasonal A/H3N2
0
0
     Influenza A untyped
0
5
   Influenza B
2
3
Total Positive other Resp. Viruses*
12
68


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


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WA Emergency Departments
The number of respiratory viral presentations reported in WA EDs have been slightly higher than in previous years, however the current trend appears to be consistent with previous years (Figure 2). In the fortnight ending 24 April 2011 there were 703 respiratory viral presentations, including 47 admissions.

Figure 2. Number of respiratory viral presentations to WA EDs from 1 January 2008 to 24 April 2011, by week

Figure 2.	Number of respiratory viral presentations to WA EDs from 1 January 2008 to 24 April 2011, by week

Source: WA ‘Virus Watch’ Report



NSW Emergency Departments
In April 2011 there were 146 ILI presentations to NSW EDs (a rate of 1.0 per 1,000 presentations), which was slightly more than the 124 presentations seen in March 2011. Compared to previous years for the same period, the number of presentations observed in April 2011 were higher than the 85 presentations seen in April 2010, however they were similar to April totals in 2006-2009.1

National Health Call Centre Network
The number of ILI-related calls to the National Health Call Centre Network (NHCCN) in this reporting period continued to be low and similar to previous weeks. The percentage of total calls remained low and stable (Figure 3).

Figure 3. Number of calls to the NHCCN related to ILI and percentage of total calls, Australia, 1 January 2009 to 29 April 2011

Figure 3. Number of calls to the NHCCN related to ILI and percentage of total calls, Australia, 1 January 2009 to 29 April 2011

Note: national data does not include QLD and VIC
Source: NHCCN data


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Laboratory Confirmed Cases Notified to Health Departments

During this reporting period there were 175 influenza notifications reported to the NNDSS (94 in Qld, 29 in SA, 14 in Tas, 13 in Vic, 12 in NSW, 9 in WA, and 4 in the NT). They included 103 cases of influenza A (untyped), 31 cases of pandemic (H1N1) 2009, 3 cases of influenza A/H3N2, 37 of influenza B and 1 of influenza untyped (Figure 4).

There have been 3,141 confirmed cases of influenza of all types diagnosed during 2011 up to
29 April (Figure 4). Of these, 1,465 (47%) have been sub-typed as influenza A (untyped), 722 (23%) as pandemic (H1N1) 2009, 508 (16%) as type A/H3N2, and 19 (<1%) were type A&B. A further 395 (13%) have been characterised as influenza type B and 32 (1%) were untyped.

Please note, Northern Territory sub-typing results reported to the NNDSS as "Influenza A/Not Pandemic" have been counted as influenza A/H3N2 notifications.
Figure 4. Laboratory confirmed cases of influenza in Australia, 1 January 2005 to 29 April 2011

Figure 4. Laboratory confirmed cases of influenza in Australia, 1 January 2005 to 29 April 2011

Source: NNDSS 2011


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As at 29 April 2011, the number of laboratory confirmed cases of influenza in 2011 was 1,530 in Qld, 406 in NSW, 391 in Vic, 329 in the NT, 243 in SA, 196 cases in WA, 29 cases in Tas and 17 cases in the ACT (Figure 5). All jurisdictions have reported higher than usual numbers of notifications for this time of the year, especially in the Northern Territory and Queensland. Based on sub-typing information, Queensland are reporting circulation of mostly pandemic (H1N1) 2009 and type A/H3N2. The majority of the Northern Territory cases have been type A/H3N2. A breakdown of trends by state and territory, highlights that in recent weeks there has been a slight decline in the number of notifications in most jurisdictions, noting that some of these declines in the past fortnight are due to lags in reporting (Figure 6).


Figure 5. Laboratory confirmed cases of influenza in Australia, 1 January to 29 April 2011, by state, by week

Figure 5.	Laboratory confirmed cases of influenza in Australia, 1 January to 29 April 2011, by state, by week

Figure 6. State breakdowns of laboratory confirmed cases of influenza, 1 January to 29 April 2011, by week

Figure 6. 	State breakdowns of laboratory confirmed cases of influenza, 1 January to 29 April 2011, by week, australian capital territory

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Figure 6. 	State breakdowns of laboratory confirmed cases of influenza, 1 January to 29 April 2011, by week, new south wales

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Figure 6. 	State breakdowns of laboratory confirmed cases of influenza, 1 January to 29 April 2011, by week, northern territory

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Figure 6. 	State breakdowns of laboratory confirmed cases of influenza, 1 January to 29 April 2011, by week, queensland

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Figure 6. 	State breakdowns of laboratory confirmed cases of influenza, 1 January to 29 April 2011, by week, tasmania

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Figure 6. 	State breakdowns of laboratory confirmed cases of influenza, 1 January to 29 April 2011, by week, south australia

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Figure 6. 	State breakdowns of laboratory confirmed cases of influenza, 1 January to 29 April 2011, by week, victoria
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Figure 6. 	State breakdowns of laboratory confirmed cases of influenza, 1 January to 29 April 2011, by week, western australia

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Deaths associated with influenza and pneumonia

Nationally notified influenza associated deaths
In 2011, 3 influenza associated deaths have been notified to the NNDSS, with all cases having pandemic (H1N1) 2009.

NSW
Death registration data show that for the week ending 8 April 2011, there were 1.3 pneumonia or influenza associated deaths per 100,000 deaths in NSW, which is below the seasonal threshold for this period of 1.4 per 100,000 deaths (Figure 7).

NSW death registration data cross-matched with laboratory cases of influenza show that up to 8 April 2011 there was one person with laboratory confirmed influenza who died.1

Figure 7. Rate of deaths classified as influenza and pneumonia from the NSW Registered Death Certificates, 2006 to 8 April 2011

Figure 7. 	Rate of deaths classified as influenza and pneumonia from the NSW Registered Death Certificates, 2006 to 8 April 2011

Source: NSW ‘Influenza Monthly Epidemiology Report’


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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 1 May 2011, there were 377 Australian influenza isolates subtyped by the WHO CC with the majority of isolates subtyped as pandemic (H1N1) 2009 (45%) or type A/H3N2 (39%) (Table 2).

Table 2. Typing of influenza isolates from the WHO Collaborating Centre, from 1 January 2011 to 1 May 2011

Type/Subtype
ACT NSW NT Qld SA Tas Vic WA TOTAL
Pandemic (H1N1) 2009
0
5
28
102
0
1
14
20
170
A(H3N2)
0
1
45
85
0
1
4
10
146
B
0
3
32
19
0
0
3
4
61
Total
0
9
105
206
0
2
21
34
377

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 but there has been insufficient testing to date to determine any general trends.
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Antiviral Resistance

The WHO Collaborating Centre in Melbourne has reported that from 1 January 2011 to 1 May 2011, one isolate (out of 668 tested) has shown resistance to oseltamivir or zanamivir by enzyme inhibition assay (EIA). One isolate out of a total of 7 pandemic H1N1 (2009) tested, have shown the H275Y mutation known to confer resistance to oseltamivir.

3. International Influenza Surveillance

The WHO has reported that influenza activity in the Northern Hemisphere temperate regions has returned to baseline levels in most areas, indicating the season is now ending. In countries in the tropical zone, influenza activity is generally low with localised transmission of influenza A/H3N2 in central Africa. Reports from National Influenza Centres from 69 countries report that from 27 March – 9 April 2011, 51% of specimens reported as influenza positive were influenza type A and 49% were influenza type B. Of the sub-typed influenza A viruses, 60% were pandemic (H1N1) 2009 and 40% were influenza A(H3N2).2

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

Sentinel 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 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.

National Notifiable Diseases Surveillance System (NNDSS)

Laboratory confirmed influenza (all types) is notifiable in all jurisdictions in Australia. Confirmed cases of influenza are notified through NNDSS by all jurisdictions.

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

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

Data are provided weekly to the Communicable Disease 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 6 is extracted from the ‘Weekly Influenza Report, NSW’

5. References

1. NSW Influenza Monthly Epidemiology Report, April 2011. Available from http://www.health.nsw.gov.au/resources/publichealth/infectious/influenza/pdf/20110311_monthly_report.pdf Accessed 5 May 2011.

2. WHO Influenza update – 21 April 2011. Available from http://www.who.int/csr/disease/influenza/latest_update_GIP_surveillance/en/index.html Accessed 6 May 2011