Australian influenza report 2010 - 17 to 23 April 2010 (#16/10)

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: 03 April 2010

Report No. 16
Week ending 23 April 2010

A print friendly version of this report is available as a PDF (256 KB)

Key Indicators

The counting of every case of pandemic influenza is no longer feasible in the PROTECT phase. Influenza activity and severity in the community is instead monitored by the surveillance systems listed below.

Is the situation changing?

Indicated by laboratory confirmed cases reported to NetEpi and/or National Notifiable Diseases Surveillance System (NNDSS); GP Sentinel influenza-like illness (ILI) Surveillance; and emergency department (ED) presentations of ILI at sentinel hospitals (New South Wales and Western Australia).

Laboratory data are used to determine the proportion of pandemic (H1N1) 2009 influenza 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 as well as 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 or shift from laboratory surveillance.


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Summary

  • In 2010, as at 23 April, there have been 60 confirmed cases of pandemic (H1N1) 2009 influenza reported in Australia, bringing the total of confirmed cases to 37,696 since May 2009. There have been no new confirmed cases of pandemic (H1N1) 2009 influenza reported in Australia during this reporting period.
  • Of the 448 confirmed cases of influenza diagnosed during 2010 up to 23 April, 13% have been sub-typed as pandemic (H1N1) 2009, 72% as type A not sub-typed and 0.9% as A/H3N2. A further 11% have been characterised as type B.
  • Sentinel hospitals have reported no hospitalisations associated with pandemic (H1N1) 2009 influenza this reporting period.
  • Levels of influenza-like illness (ILI) in the community remain relatively low and reporting from laboratories indicates that little of this ILI is due to influenza. Respiratory syncytial virus was the most common respiratory virus diagnosed by NSW and WA sentinel laboratories in the last reporting period.
  • Pandemic (H1N1) 2009 influenza accounted for 79.9% of all influenza A viruses subtyped globally in the last reporting week. Seasonal Influenza B viruses are predominant across East Asia, Central Africa and Northern and Eastern Europe.
  • In China, Influenza B accounted for more than 88.7% of all influenza viruses detected in the week to 11 April 2010. From 1 September 2009 to 11 April 2010, 90.3% of antigenically characterised influenza B viruses were B/Victoria and 9.7% were B/Yamagata viruses. Of the B/Victoria viruses, 47.7% were related to B/Brisbane/60/2008, which is included in the 2010 Southern Hemisphere seasonal influenza vaccine, and 52.3% were related to B/Malaysia/2506/2004-like.
  • As at 18 April 2010, the WHO Regional Offices reported over 17,853 deaths associated with pandemic (H1N1) 2009 influenza worldwide. In the Northern Hemisphere the areas of highest transmission are West and Central Africa.
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1. Influenza activity in Australia

Laboratory Confirmed Cases

Pandemic influenza activity remains low and sporadic cases of pandemic influenza continue to be reported without evidence of sustained community transmission. There were no laboratory confirmed pandemic (H1N1) 2009 cases diagnosed during this reporting period in Australia (Figure 1).

In the same period, there have been a total of 24 cases diagnosed as influenza. They included 20 of type A not sub-typed (15 in Queensland, four in South Australia and one in the
Australian Capital Territory), three of type B (all in Queensland) and one un-typed (in
Western Australia).

There has been a total of 37,696 confirmed cases of pandemic (H1N1) 2009 in Australia as at 23 April 2010, including 191 pandemic influenza-associated deaths. Of these, 37,636 cases were reported in 2009 and 60 cases were reported in 2010.

Figure 1. Laboratory confirmed cases of pandemic (H1N1) 2009 and total influenza in Australia, to 23 April 2010

Figure 1. Laboratory confirmed cases of pandemic (H1N1) 2009 and total influenza in Australia, to 23 April 2010

Note: Total influenza series starts on 1 January 2010.
Source: NetEpi (2009; NSW 2010) and NNDSS (2010)


There have been 448 confirmed cases of influenza of all types diagnosed during 2010 up to 23 April. Of those, 60 (13%) have been sub-typed as pandemic (H1N1) 2009, 324 (72%) as influenza type A not sub-typed and 4 (0.9%) as A/H3N2. A further 51 (11%) have been characterised as influenza type B (Figure 2).
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Influenza type A not further sub-typed is the predominant type in Australia to date this year. While it is expected that this is pandemic influenza (H1N1) 2009, it has a higher age profile (median age 40 years) than cases confirmed as the pandemic (H1N1) 2009 strain (27 years in 2010).
The proportion of women diagnosed with Influenza type A not further sub-typed is also higher (51%) compared to that diagnosed with the pandemic (H1N1) 2009 strain (42% in 2010).

Figure 2. Laboratory confirmed cases of influenza (pandemic (H1N1) 2009 and seasonal) in Australia, 1 January 2010 to 23 April 2010, by week and type

Figure 2. Laboratory confirmed cases of influenza (pandemic (H1N1) 2009 and seasonal) in Australia, 1 January 2010 to 23 April 2010, by week and type

Source: NNDSS and NetEpi (NSW).


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Influenza-Like Illness

Sentinel General Practice Surveillance

Combined data available from the Australian Sentinel Practices Research Network (ASPREN) and the Northern Territory GP surveillance system up until 18 April 2010 show that national ILI consultation rates remain low, and are below levels seen in 2008 and 2009.

In the last week, the presentation rate to sentinel GPs in Australia was approximately four cases per 1,000 consultations (Figure 3).

Figure 3. Weekly rate of ILI reported from GP ILI surveillance systems from 1 January 2007 to 18 April 2010*

Figure 3. Weekly rate of ILI reported from GP ILI surveillance systems from 1 January 2007 to 18 April 2010

* Delays in the reporting of data may cause data to change retrospectively. As data from the NT surveillance system is combined with ASPREN data for 2010, rates may not be directly comparable across 2007, 2008 and 2009.
SOURCE: ASPREN, and NT GP surveillance system.


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WA Emergency Departments

The number of respiratory viral presentations reported in Western Australian EDs decreased slightly in the week ending 18 April 2010. Levels are similar to those seen at the same time in 2008 (Figure 4).

Figure 4. Number of respiratory viral presentations to Western Australia EDs from 1 January 2007 to 18 April 2010 by week

Figure 4. Number of respiratory viral presentations to Western Australia EDs from 1 January 2007 to 18 April 2010 by week

Source: WA ‘Virus Watch’ Report



NSW Emergency Departments

In March 2010, there were 90 presentations of ILI to New South Wales EDs. This is a similar number of presentations to the previous month (88 presentations), but more than that recorded in March 2009 (49 presentations).
There were five hospital admissions following presentation to EDs with ILI in March 2010, compared with four in February 2010 and one in March 2009.

Source: NSW Health ‘Influenza Monthly Epidemiology Report1


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Flutracking

Flutracking, a national online system for collecting data on ILI in the community, reported that in the week ending 25 April 2010 ILI levels have remained low and relatively stable at the national level (Figure 5).

Figure 5. Rate of ILI symptoms and absence from regular duties among Flutracking participants by week (from 3 May 2009 to week ending 25 April 2010)

Figure 5. Rate of ILI symptoms and absence from regular duties among Flutracking participants by week (from 3 May 2009 to week ending 25 April 2010)

Source: Flutracking Interim Weekly Report



National Health Call Centre Network

There were 43 ILI-related calls to the National Health Call Centre Network (NHCCN) in the week ending 23 April 2010, compared to 60 calls in the previous reporting period. The number of calls is currently at baseline levels (Figure 6).

Figure 6. Number of calls to the NHCCN related to ILI, Australia, 1 January 2009 to 16 April 2010

Figure 6. Number of calls to the NHCCN related to ILI, Australia, 1 January 2009 to 16 April 2010

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


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Deaths associated with influenza and pneumonia

Death registration data show that as at 12 March 2010, there were 69 pneumonia or influenza deaths per 1,000 deaths in NSW, which is below the seasonal threshold of 99 per 1,000 (Figure 7).

Figure 7. Rate of deaths classified as influenza and pneumonia from the NSW Registered Death Certificates, 2005 – 2010

Figure 7. Rate of deaths classified as influenza and pneumonia from the NSW Registered Death Certificates, 2005 – 2010

Source: NSW ‘Influenza Monthly Epidemiology Report’


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Absenteeism

The most recent data indicate that in the week ending 14 April 2010, national absenteeism rates remained similar to levels seen in previous years (Figure 8).

Figure 8. Rates of absenteeism (greater than 3 days absent), national employer, from 28 January 2007 to 14 April 2010, by week.

Figure 8. Rates of absenteeism (greater than 3 days absent), national employer, from 28 January 2007 to 14 April 2010, by week. <

SOURCE: Absenteeism data


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Sentinel Laboratory Surveillance - confirmed influenza notifications

Results from sentinel laboratory surveillance systems for this reporting period show that two of the respiratory tests conducted over this period were positive for influenza. Both were pandemic (H1N1) 2009 (Table 1).

Table 1. Laboratory respiratory tests that tested positive for influenza
  ASPREN* – national NSW NIC WA NIC NT
(Reported by WA NIC)
Number of specimens tested
1
67
74
N/A
Number tested which were Influenza A
0
0
2
0
Number tested which were pandemic     (H1N1) 2009
0
0
2
0
Number tested which were seasonal   A/H1N1
0
0
0
0
Number tested which were A/H3N2
0
0
0
0
Number tested which were Influenza A untyped
0
0
0
0
Number tested which were Influenza B
0
0
0
0

*ASPREN tests are collected every Tuesday. Results are reported for a rolling fortnight as data changes retrospectively. [/p>]

Respiratory syncytial virus was the most common respiratory virus diagnosed by NSW and WA sentinel laboratories in the last reporting period.
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2. Overview of influenza severity - to 23 April 2010a

While pandemic (H1N1) 2009 is generally considered a mild disease at the community level, it has had serious consequences at the acute end of the disease. Figures of hospitalisations, ICU admissions and deaths are currently used as indicators of the severity of the disease in Australia (Table 2).

Note that while the analysis of severity is on-going, updates are presented as required when there are significant changes detected. With the current low levels of pandemic (H1N1) 2009 influenza activity in Australia it is anticipated that the indicators of pandemic severity will not vary significantly.



Pandemic (H1N1) data for 2009 are currently being finalised through cleaning and validation processes. It is possible that these processes will result in some changes in the data presented here. Validated data will be progressively reported as these steps are completed.

Table 2. Summary of severity indicators of pandemic (H1N1) in Australia, 2009 and 2010 up to 23 April 2010

2009#  2010a
  Confirmed pandemic
(H1N1) 2009 cases
Hospitalised cases ICU cases Deaths Confirmed (H1N1) 2009 cases
Total number
37,636
13% (4,992/37,636) confirmed cases)
14%
(681/4,992 hospitalisations)
191
60
Crude rate per 100,000 population
172.1
22.8
3.1
0.9
0.3
Median age (years)
21
31
44^
53^
27
Females
51% (19,139/37,636)
51% (2,528/4,992)
53%
(364/681)
44%
42%
(25/60)
Vulnerable groups (Indigenous persons, pregnant women & individuals with at least 1 co-morbidity)
n/a
58% (2,892/4,992)
74%
(504/681)
67%
n/a
Indigenous people~
11% (3,877/34,750)
20%
(808/4,048)
19%
(102/533)
13%
2%
(1/60)
Pregnant women*
n/a
27%
(287/1,056 hospitalised females aged
15-44 years)
16%
(47/289) hospitalised pregnant women)
4%
n/a
Cases with at least 1 co-morbidity
n/a
46% (2,303/4,992)
67%
(457/681)
62%
n/a

a Data for 2009 from NetEpi, Data for 2010 from NNDSS and NetEpi (NSW).
#Data are extracted from a number of sources depending on the availability of information. Figures used in the analysis have been provided in parentheses. Data are not always complete for each summarised figure.
~The denominator for this row is the number of confirmed cases for which Indigenous status is known.
* Includes women in the post-partum period.
^ Validation of data has identified anomalies affecting median ages for ICU cases and deaths in reports #28-33 2009 and report #1 2010. Correction has resulted in a change in the median ages of ICU cases and deaths from report #2, 2010.


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Influenza Hospitalisations

The Influenza Complications Alert Network (FluCAN) reported no influenza hospitalisations for the week ending 23 April 2010. However, for the period 1 March to 23 April 2010, FluCAN has reported three influenza hospitalisations. Of those, two were associated with pandemic (H1N1) 2009 and one was associated with Type A/H3N2 (Table 3 and Figure 9). One of these hospitalisations involved ICU admission. FluCAN data has been collected from 11 participating sentinel hospitals from all jurisdictions except NT.

Table 3. Number of influenza hospitalisations, sentinel hospitals, Australia, 1 March to 23 April 2010

Type of influenza
Week ending
23 April 2010
Total
1 March – 23 April
Pandemic (H1N1)
0
2
Type A/H3N2
0
1
All types
0
3

Source: Influenza Complications Alert Network (FluCAN). Data are from 11 sentinel hospitals from all jurisdictions except NT.

Figure 9. Number of influenza hospitalisations, sentinel hospitals, Australia, 1 March to 23 April 2010

Figure 9. Number of influenza hospitalisations, sentinel hospitals, Australia, 1 March to 23 April 2010

Source: FluCAN data from 11 sentinel hospitals in all jurisdictions except ACT and NT
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3. Virology

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

From 1 January 2010 to 18 April 2010, there were 30 Australian influenza isolates subtyped by the WHO CC (Table 4). Twenty were Pandemic (H1N1) 2009, three were A(H3N2) and seven were type B.

Table 4. Typing of influenza isolates from the WHO Collaborating Centre, from 1 January 2010 to 18 April 2010

Type/Subtype
ACT NSW NT Qld SA Tas Vic WA TOTAL
A(H1N1)
0
0
0
0
0
0
0
0
0
Pandemic (H1N1) 2009
1
0
3
7
0
1
6
2
20
A(H3N2)
0
0
0
0
0
0
3
0
3
B
0
0
0
0
0
0
7
0
7
Total
1
0
3
7
0
1
16
2
30

SOURCE: WHO CC
Please note: There may be up to a months delay on reporting of samples.
Isolates tested by the WHO CC are not necessarily a random sample of all those in the community, hence proportions of pandemic (H1N1) 2009 to seasonal are not representative of the proportions circulating.



Of the 30 subtyped influenza isolates, 11 have been confirmed as pandemic A/H1N1 2009 (A/California/7/2009-like).
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INTERNATIONAL UPDATES

The Global Influenza Surveillance Network (GISN) continues to monitor the global circulation of influenza viruses, including pandemic, seasonal and other influenza viruses infecting, or with the potential to infect, humans. Since the beginning of the pandemic on 19 April 2009 to 17 April 2010, 155 countries shared a total of 25,206 specimens (19,352 clinical samples and 5,864 virus isolates) with WHO Collaborating Centres for further characterisation.1
Pandemic (H1N1) 2009 influenza virus accounted for 79.9% of all influenza A viruses subtyped globally. Seasonal Influenza B viruses are now the predominant circulating influenza viruses across East Asia, Central Africa and Northern and Eastern Europe.

In China, influenza B accounted for 88.7% of all influenza viruses detected in the week to 11 April 2010. From 1 September 2009 to 11 April 2010, 2790 influenza B viruses have been antigenically characterised. Of those, 2519 (90.3%) were B/Victoria viruses; 52.3% (1318) related to B/Malaysia/2506/2004-like and 47.7% (1201) related to B/Brisbane/60/2008 (included in 2010 Southern Hemisphere seasonal influenza vaccine). The remaining 271 (9.7%) were B/Yamagata viruses related to B/Florida/4/2006-like.2
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ANTIVIRAL RESISTANCE

Pandemic (H1N1) 2009

The WHO has reported that 285 oseltamivir resistant pandemic (H1N1) 2009 viruses had been detected and characterised worldwide. All but one of these isolates showed the same H275Y mutation but were sensitive to zanamivir. One case of pandemic (H1N1) 2009 in an immunocompromised child has shown reduced susceptibility to zanamivir and oseltamivir due to an amino acid mutation in the neuraminidase. No onward transmission was detected.3

The WHO Collaborating Centre in Melbourne has reported that from 1 January 2010 to 25 April 2010, no isolates have shown resistance to oseltamivir by enzyme inhibition assay (EIA) and two clinical specimens collected in Australia have shown the H275Y mutation known to confer resistance to oseltamivir (Table 5).

Table 5. Neuraminidase resistance testing of Australian pandemic (H1N1) 2009 influenza viruses

  2009 2010
  Viral isolates Clinical specimens Viral isolates Clinical specimens
No. tested
587
276
2
3
EIA Resistant
4
N/A
0
N/A
H275Y mutation
N/A
9
N/A
2

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Seasonal Influenza

The last WHO report on resistance of seasonal influenza strains to oseltamivir was released on 4 June 2009, during the Northern Hemisphere influenza season 2008-2009 and stated that 96% of seasonal influenza A (H1N1) isolates tested from 36 countries worldwide were resistant to oseltamivir.4 Australian oseltamivir resistance testing data on seasonal influenza strains are shown in Table 6.

Table 6. Resistance Testing – Seasonal Influenza – Australia 1 January 2009 to 18 April 2010

% of H1N1 viruses % of A(H3N2) % of B viruses
92.6% (38/41) resistant to oseltamivir
0% (0/54) resistant to oseltamivir
0% (0/6) resistant to oseltamivir

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4. International Influenza Surveillance

WHO Summary as at 18 April 2010

  • There have been over 17,853 deaths associated with pandemic (H1N1) 2009 worldwide.
  • Northern Hemisphere
      • The most active areas of pandemic influenza virus transmission are in parts of West and Central Africa, however, transmission is also still occurring in South East Asia and Central America.
      • Seasonal influenza type B viruses have been increasingly detected over a larger area and are now the predominant circulating influenza viruses across East Asia, Central Africa and Northern and Eastern Europe.
          • Southern Hemisphere
      • Chile has reported regional increases in ILI activity for the past four weeks. In some areas, ILI levels are above the epidemic threshold.
      • In Australia and New Zealand, there is no evidence yet of the start of winter-time community transmission of the influenza virus.

    Recent influenza activity in selected areas of the Northern and Southern Hemispheres is shown in Table 7.

    Table 7. International influenza surveillance by country/region for the most recent reporting week

    Country/region

    End date of most recent reporting week in 2010

    Overall influenza activity level

    Proportion of GP visits that were for ILI

    Proportion of

    Respiratory tests positive for Influenza

    Influenza which was influenza A

    Influenza A which was Pandemic (H1N1) 2009

    Influenza
    A which was
    untyped

    Northern Hemisphere
    USA5
    17 April
    Low
    1.1%
    2.1%
    94.6%
    57.1%
    42.9%
    Canada6
    17 April
    Low
    0.9%
    0.07%
    --^
    --^
    --^
    Europe7
    11 April
    Low
    Not reported
    7.6%
    11.1%
    0.0%
    100%
    UK8
    18 April
    Low
    ≤0.03%
    15.0%
    66.6%
    100.0%
    0.0%
    China2
    11 April
    Not reported
    3.4% - 3.9%
    16.6%
    6.5%
    34.3%
    0.0%
    Southern Hemisphere*
    NZ9
    25 April
    Low
    0.02%
    0.06%
    --^
    --^
    --^
    Australia
    23 April
    Low
    0.4%
    0.7%**
    83.3%***
    0.0%***
    100%***

    ^Percentages not calculated due to very small numbers.
    * Chile and Argentina have not been included in this table this reporting period, because the online influenza surveillance reports for these countries have not been updated since January and February, respectively.
    **Source: Sentinel Laboratory Surveillance (see Table 1)
    ***Source: NNDSS (see Figure 2)


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    5. 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. 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

    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 does not reflect how many people in the community have acquired pandemic (H1N1) 2009 infection.

    NetEpi

    In 2009, NetEpi, a web-based outbreak case reporting system for pandemic (H1N1) 2009, was used as the primary source of enhanced data on confirmed cases, hospitalisations and ICU admissions in all jurisdictions. In 2010, only data for NSW are sourced from NetEpi.

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

    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 except NSW. NSW data are sourced from NetEpi.

    Data Analysis

    Analysis of confirmed influenza cases is conducted on combined NetEpi and NNDSS data. Analysis of morbidity (hospitalisations and ICU admissions) and mortality data in 2009 has been conducted on combined NetEpi and QLD hospitalisation data.

    Laboratory Surveillance data

    Laboratory testing data are extracted from the ‘NSW Influenza Report,’ and the ‘The 2009 Victorian Influenza Vaccine Effectiveness Audit Report’ (VIDRL) ‘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 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.
    Further information on Sentinel GPs’ Influenza Surveillance and ASPREN activities are available at www.dmac.adelaide.edu.au/aspren
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    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 ‘Influenza Monthly Epidemiology Report, NSW’. This report is provided monthly. The New South Wales Influenza Surveillance Program collects data from 49 EDs across New South Wales.

    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.

    National Health Call Centre Network

    A national organisation provides call centre data for calls relating to ILI or influenza. Data are provided daily and are collated weekly and have been presented in this report to show the pattern of calls to this Call Centre over the 2009 season. Data is available for all jurisdictions other than QLD and VIC.

    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.
    Data have been provided weekly and have been presented in this report to show the pattern of self reported ILI in the community over the 2009 season.

    Further information on FluTracking is available at www.flutracking.net/index.html

    FluCAN

    The Influenza Complications Network (FluCAN) collects detailed clinical information on all hospitalised cases of influenza and pneumonia from a sample of 13 sentinel hospitals across Australia. The data for this reporting period are sourced only from eleven hospitals and do not include NT.
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    6. References


    1. WHO Pandemic (H1N1) 2009 - Update 96 & Virological Surveillance Weekly Update. Available from http://www.who.int/csr/don/en/ Accessed 29 April 2010.
    2. Chinese National Influenza Centre Influenza Weekly Report 11 April 2010. Available from: http://www.cnic.org.cn/eng/ Accessed 20 April 2010.
    3. EuroFlu Weekly Electronic Bulletin. Week 13 ending 4 April 2010. Available from: http://www.euroflu.org/cgi-files/bulletin_v2.cgi Accessed 20 April 2010.
    4. WHO Influenza A virus resistance to oseltamivir and other antiviral medicines, 4 June 2009. Available from: http://www.who.int/csr/disease/influenza/2008-9nhemisummaryreport/en/index.html Accessed 29 April 2010.
    5. CDC FluView Weekly report, Week 15 ending 17 April 2010. Available from: http://www.cdc.gov/flu/weekly/ Accessed 29 April 2010.
    6. Canada FluWatch Weekly report, week 15 ending 17 April 2010. Available from:
    http://www.phac-aspc.gc.ca/fluwatch/09-10/index-eng.php Accessed 29 April 2010.
    7. ECDC pandemic update, week 14 ending 11 April 2010. Available from: http://ecdc.europa.eu/en/activities/surveillance/EISN/Pages/EISN_Bulletin.aspx Accessed 29 April 2010.
    8. HPA weekly pandemic flu media update. Week 16, ending 22 April 2010. Available from: http://www.hpa.org.uk/web/HPAweb&Page&HPAwebAutoListName/Page/1243928258560 Accessed 29 April 2010.
    9. New Zealand Ministry of Health Influenza Weekly Update. Week 16, ending 25 April 2010. Available from: http://www.surv.esr.cri.nz/virology/influenza_weekly_update.php Accessed 29 April 2010.