Australian influenza report 2010 - 9 July 2010 (#27/10)

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: July 2010

Report No. 27

Week ending 9 July 2010

A print friendly version of this report is available as a PDF (217 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
gene drift or shift from laboratory surveillance.

Summary

  • Levels of influenza-like illness (ILI) in the community are continuing to show signs of increasing through some surveillance systems (ASPREN, absenteeism, WA and NSW Emergency Departments and NHCCN calls).
  • Reporting from laboratories suggests that influenza activity is increasing. The most common respiratory viruses diagnosed by sentinel laboratories this reporting period were respiratory syncytial virus (RSV) in WA and NSW and picornavirus in VIC.
  • Of the 1,247 confirmed cases of influenza of all types diagnosed during 2010 up to 9 July, 157 (13%) have been sub-typed as pandemic (H1N1) 2009, 945 (76%) as influenza type A not sub-typed, 9 (1%) as A/H3N2 and 8 (1%) as type A&B. A further 110 (9%) have been characterised as influenza type B and 18 (1%) have been untyped.
  • This reporting period, sentinel laboratory reporting suggests circulation of A(H3N2) as well as pandemic (H1N1) 2009 in the community.
  • Sentinel hospitals have reported two hospitalisations for influenza, with ANZICS also reporting three ICU admissions for influenza during this period.
  • In 2010, there have been 157 confirmed cases of pandemic (H1N1) 2009 influenza reported in Australia, bringing the total of confirmed cases to 37,793 since May 2009. There have been 12 new confirmed cases of pandemic (H1N1) 2009 influenza diagnosed and reported in Australia (Qld, NT and WA) during this reporting period.
  • In China, influenza B accounted for 53.5% of influenza viruses detected in the week to 4 July 2010. Of these, approximately 50.8% are the same strain as that in the 2010 Southern Hemisphere vaccine.
  • As at 27 June 2010, the WHO Regional Offices have reported over 18,311 deaths associated with pandemic (H1N1) 2009 influenza worldwide. Current pandemic influenza transmission remains low.
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1. Influenza activity in Australia

Geographic spread of influenza and ILI – Jurisdictional Surveillance

In the fortnight ending 9 July 2010, influenza and ILI activity as reported by state and territory Health Departments indicated that there was 'sporadic' activity in four states (NSW, VIC, QLD and SA), 'local' activity in WA and NT, and TAS reported 'syndromic only' (Figure 1).

'Syndromic only' activity is defined as an increase in syndromic surveillance systems with no laboratory confirmed cases. 'Sporadic' activity is defined as small numbers of laboratory-confirmed influenza cases or a single laboratory-confirmed influenza outbreak during the reporting period, but no increase in cases in syndromic surveillance systems. 'Local' activity is defined as outbreaks of influenza or increases in cases in syndromic surveillance systems and recent laboratory-confirmed influenza in a single region of the state.

Figure 1. Map of influenza and ILI activity, by state and territory, during fortnight ending 25 June 2010
Figure 1. Map of influenza and ILI activity, by state and territory, during fortnight ending 25 June 2010

Influenza-Like Illness

Sentinel General Practice Surveillance

In the week ending 4 July 2010, national ILI consultation rates to sentinel GPs was approximately 8 cases per 1,000 consultations (Figure 2).

Figure 2. Weekly rate of ILI reported from GP ILI surveillance systems from 1 January 2007 to 4 July 2010*
Figure 2. Weekly rate of ILI reported from GP ILI surveillance systems from 1 January 2007 to 4 July 2010*

* 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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WA Emergency Departments

Respiratory viral presentations reported in Western Australian EDs continue to show an upward trend (Figure 3). In the week ending 4 July 2010 there were 503 respiratory viral presentations, an increase compared to 459 in the previous reporting week.

Figure 3. Number of respiratory viral presentations to Western Australia EDs from 1 January 2007 to 4 July 2010 by week
Figure 3. Number of respiratory viral presentations to Western Australia EDs from 1 January 2007 to 4 July 2010 by week

Source: WA 'Virus Watch' Report


NSW Emergency Departments

In the week ending 2 July 2010, ILI presentations to NSW EDs remained low and similar to levels seen at the same time in 2008 (Figure 4). There were 14 admissions to hospital following presentation to emergency departments with ILI in June 2010.

Figure 4: ILI presentations to NSW EDs from 2007-2010, by week
Figure 4: ILI presentations to NSW EDs from 2007-2010, by week

Source: NSW Health 'Influenza Weekly Epidemiology Report


Flutracking


Flutracking, a national online system for collecting data on ILI in the community, reported that ILI levels remained low and stable in the week ending 11 July 2010 (Figure 5).

Figure 5. Rate of ILI symptoms and absence from regular duties among Flutracking participants by week, from week ending 5 May 2009 to week ending 11 July 2010
Figure 5. Rate of ILI symptoms and absence from regular duties among Flutracking participants by week, from week ending 5 May 2009 to week ending 11 July 2010

Source: Flutracking Interim Weekly Report


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National Health Call Centre Network

The number of calls to the National Health Call Centre Network (NHCCN) remained steady this reporting period (Figure 6).

Although ILI-related calls have been increasing gradually since the start of 2010, the number of ILI calls, and percent of total calls, remain at levels similar to late 2009 (Figure 6). Call numbers cannot be compared between early 2009 and early 2010 as not all call centres were online in early 2009. The difference in operating call centre numbers accounts for this apparent increase in recorded ILI calls (and baseline levels) between the two years.

Figure 6. Number of calls to the NHCCN related to ILI and percentage of total calls, Australia, 1 January 2009 to 9 July 2010
Figure 6. Number of calls to the NHCCN related to ILI and percentage of total calls, Australia, 1 January 2009 to 9 July 2010

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


Absenteeism

In the week ending 30 June 2010, there was a slight increase in absenteeism nationally compared to the previous week. This is consistent with an overall increasing trend since the beginning of 2010 (Figure 7).

Figure 7. Rates of absenteeism (greater than 3 days absent on sick leave), national employer, from 28 January 2007 to 30 June 2010, by week

Figure 7. Rates of absenteeism (greater than 3 days absent on sick leave), national employer, from 28 January 2007 to 30 June 2010, by week

SOURCE: Absenteeism data


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Laboratory confirmed influenza

Sentinel Laboratory Surveillance

Results from sentinel laboratory surveillance systems for this reporting period show that 3.2% (18/568) of the respiratory tests conducted over this period were positive for influenza, a decrease compared with 5.8% last reporting period (Figure 8).

Figure 8. Total number of specimens tested by sentinel laboratories, and proportion positive, 1 January 2010 to 9 July 2010, by week
 Figure 8. Total number of specimens tested by sentinel laboratories, and proportion positive, 1 January 2010 to 9 July 2010, by week

SOURCE: Sentinel laboratory data from ASPREN, NSW NIC, WA NIC, VIC NIC & TAS Labs


There were a total of 18 specimens positive for influenza during this period, of which 15 were pandemic (H1N1) 2009, and 3 were A/H3N2 (Table 1).

Table 1. Laboratory respiratory tests that tested positive for influenza
ASPREN – national
NSW NIC
WA NIC
NT(Reported by WA NIC)
VIC NIC
TASlaboratories
Total specimens tested
96
127
171
N/A
152
22
Positive Influenza A
1
0
12
1
4
0
Pandemic (H1N1) 2009
1
0
11
1
2
0
Seasonal A/H1N1
0
0
0
0
0
0
Seasonal A/H3N2
0
0
1
0
2
0
Influenza A untyped
0
0
0
0
0
0
Positive Influenza B
0
0
0
0
0
0
The most common respiratory virus detected
Rhinovirus
RSV
RSV
N/A
Picornavirus
N/A
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Laboratory Confirmed Cases Notified to Health Departments

During this reporting period, 50 confirmed cases of influenza were notified. They included 34 of type A not sub-typed (23 in QLD, 7 in Vic, 4 in NSW) and four of type B (all in QLD).

Pandemic influenza activity remains low, and sporadic cases of pandemic influenza continue to be reported without evidence of sustained community transmission (Figure 9). During this period, there were 12 laboratory confirmed pandemic (H1N1) 2009 cases (3 in NT, 3 in QLD and 6 in WA) diagnosed during this reporting period.

Figure 9. Laboratory confirmed cases of influenza in Australia, 1 January 2005 to 9 July 2010
Figure 9. Laboratory confirmed cases of influenza in Australia, 1 January 2005 to 9 July 2010

Source: NetEpi (2009; NSW 2010) and NNDSS (2010)
Note: The scale in this figure has been limited to 1600 notifications per week to allow for comparison
between 2010 and previous years. In 2009, notifications peaked at approximately 8,300 in Week 30.


In 2010, the distribution of influenza notifications is consistent across age groups and similar to distributions observed in 2008 (Figure 11). In 2009 the distribution of influenza notifications tended to occur in persons aged less than 55 years, with substantially higher rates observed in persons aged less than 30 years, compared to older age groups.

Figure 10. Laboratory confirmed cases of influenza (pandemic (H1N1) 2009 and seasonal) in Australia, 1 January 2008 to 9 July 2010, by age group
Figure 10. Laboratory confirmed cases of influenza (pandemic (H1N1) 2009 and seasonal) in Australia, 1 January 2008 to 9 July 2010, by age group

Source: NNDSS and NetEpi (NSW).


There have been 1,247 confirmed cases of influenza of all types diagnosed during 2010 up to 9 July. Of those, 157 (13%) have been sub-typed as pandemic (H1N1) 2009, 945 (76%) as influenza type A not sub-typed, 9 (1%) as A/H3N2 and 8 (1%) as type A&B. A further 110 (9%) have been characterised as influenza type B and 18 (1%) have been untyped (Figure 10).

Figure 11. Laboratory confirmed cases of influenza (pandemic (H1N1) 2009 and seasonal) in Australia, 1 January 2010 to 9 July 2010, by type
Figure 11. Laboratory confirmed cases of influenza (pandemic (H1N1) 2009 and seasonal) in Australia, 1 January 2010 to 9 July 2010, by type

Source: NNDSS and NetEpi (NSW).


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2. Influenza severity to 18 June 2010 1

Pandemic (H1N1) 2009

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

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.

Since the first case of pandemic (H1N1) 2009 in Australia in May 2009, there have been a total of 37,772 confirmed cases of pandemic (H1N1) 2009 in Australia as at 2 July 2010, including 191 pandemic influenza-associated deaths. Of these, 37,636 cases were reported in 2009 and 157 cases were reported in 2010.

Table 2. Summary of severity indicators of pandemic (H1N1) in Australia, 2009 and 2010 (up to 9 July 2010)
2009#
2010a
Confirmed pandemic
(H1N1) 2009 cases
Hospitalised cases ICU casesDeaths Confirmed (H1N1) 2009 cases
Total number37,63613% (4,992/37,636) confirmed cases)14%
(681/4,992 hospitalisations)
191157
Crude rate per 100,000 population172.122.83.10.90.7
Median age (years)213144^53^26
Females51% (19,139/37,636) 51% (2,528/4,992)53%
(364/681)
44%47.1%
(74/157)
Vulnerable groups (Indigenous persons, pregnant women & individuals with at least 1 co-morbidity)n/a58% (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%6.4%
(9/140)
Pregnant women*n/a27%
(287/1,056 hospitalised females aged
15-44 years)
16%
(47/289) hospitalised pregnant women)
4% n/a
Cases with at least 1 co-morbidityn/a46% (2,303/4,992)67%
(457/681)
62%n/a
aData 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. In 2010, 27 cases had Indigenous status unknown.
*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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1Note 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 associated severity will not vary significantly.


Influenza Hospitalisations

The Influenza Complications Alert Network (FluCAN) reported two pandemic (H1N1) 2009 influenza hospitalisations from selected hospitals for the week ending 9 July 2010. For the period of 1 March to 9 July 2010, FluCAN has reported a total of 18 influenza hospitalisations (Figure 12). Of those, 10 have been associated with pandemic (H1N1) 2009, including 3 with ICU admission.

Figure 12. Number of influenza hospitalisations, sentinel hospitals, Australia, 1 March to 9 July 2010
Figure 12. Number of influenza hospitalisations, sentinel hospitals, Australia, 1 March to 9 July 2010

Source: Influenza Complications Alert Network (FluCAN). Data from 11 sentinel hospitals from all jurisdictions except NT.
Note: two cases have been retrospectively added for the first week of March.


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Intensive care admissions

The Australian and New Zealand Intensive Care Society (ANZICS) has reported a total of ten ICU admissions for influenza in 2010, of which three occurred during this reporting period. In total, five ICU admissions have been associated with pandemic (H1N1) 2009 and five with influenza A (not subtyped) (Figure 13).

Of the 5 pandemic (H1N1) 2009 ICU admissions in 2010, 3 had known co-morbidities and the median age at admission was 29 years (range 10-59).

Figure 13. Number of ICU admissions for influenza, ANZICS, Australia, 1 January to 9 July 2010
Figure 13. Number of ICU admissions for influenza, ANZICS, Australia, 1 January to 9 July 2010

Source: Australian and New Zealand Intensive Care Society (ANZICS) data base


Deaths associated with influenza and pneumonia


Death registration data show that for the week ending 18 June 2010, there were 93 pneumonia or influenza associated deaths per 1,000 deaths in NSW, which is below the seasonal threshold of 122 per 1,000 (Figure 14).

Figure 14. Rate of deaths classified as influenza and pneumonia from the NSW Registered Death Certificates, 2005 to 18 June 2010
Figure 14. Rate of deaths classified as influenza and pneumonia from the NSW Registered Death Certificates, 2005 to 18 June 2010

Source: NSW 'Influenza Monthly Epidemiology Report'


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3. Virology

Typing and antigenic characterisation - WHO Collaborating Centre for Reference & Research on Influenza (WHO CC) in Melbourne

From 1 January to 11 July 2010, there were 94 Australian influenza isolates subtyped by the WHO CC (Table 3).

Table 3. Typing of influenza isolates from the WHO Collaborating Centre, from 1 January 2010 to 11 July 2010
Type/SubtypeACTNSWNTQLDSATASVICWATOTAL
A(H1N1)000000000
Pandemic (H1N1) 200911381101101173
A(H3N2)0002004410
B0100009111
Total12381301231694

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, hence proportions of pandemic (H1N1) 2009 to seasonal are not representative of the proportions circulating.


Antigenic characterisation of 13 pandemic (H1N1) 2009 isolates has shown 12 to be the A/California/7/2009-like strain and one a low reactor version of this strain. Antigenic characterisation of 1 type A/H3N2 isolate has shown to be the A/Perth/16/2009-like low reactor version of the strain (Attachment A).

International Virology

In the week ending 26 June 2010, based on FluNet reporting by National Influenza Centres from 29 countries, 45.5% of positive specimens were typed as influenza B and 54.5% were typed as influenza A. In the Northern Hemisphere, the number of influenza B detections exceeded that of influenza A. Influenza B detections were particularly high in China (69.3% of all influenza detections) and the Russian Federation (93.7%). In the Southern Hemisphere, there is an increasing number of influenza A virus detections with co-circulation of pandemic a(H1N1) and seasonal A(H3N2) viruses.

In China, influenza B accounted for 56.5% of all influenza viruses detected in the week to 4 July 2010. From 1 January 2010 to 4 July 2010, 3070 influenza B viruses have been antigenically characterised. Of those, 2,655 (86.5%) were B/Victoria viruses, including 49.2% (1307) related to B/Malaysia/2506/2004-like and 50.8% (1348) related to B/Brisbane/60/2008 (included in 2010 Southern Hemisphere seasonal influenza vaccine). The remaining 415 (13.5%) were B/Yamagata viruses related to B/Florida/4/2006-like.<sup>]1

Antiviral Resistance – Pandemic (H1N1) 2009

The WHO has reported that 298 oseltamivir resistant pandemic (H1N1) 2009 viruses have been detected and characterised worldwide since May 2009. All of these isolates showed the same H275Y mutation and all remain sensitive to zanamivir.2

The WHO Collaborating Centre in Melbourne has reported that from 1 January 2010 to 11 July 2010, no isolates (out of 28 tested) have shown resistance to oseltamivir or zanamivir by enzyme inhibition assay (EIA) and two isolates (out of 33 tested) have shown the H275Y mutation known to confer resistance to oseltamivir.

4. International Influenza Surveillance

The WHO has reported that have been over 18,311 deaths associated with pandemic (H1N1) 2009 influenza worldwide. Overall pandemic activity worldwide remains low.2

Northern Hemisphere

  • Pandemic and seasonal influenza viruses have been detected sporadically or at very low levels during the past month.2
  • Active circulation of pandemic influenza virus persists in South and Southeast Asia, the Caribbean and West Africa.2
  • Increasing seasonal influenza activity has been observed in several countries in Central America.2
  • In China, Hong Kong, Taiwan and the Republic of Korea, seasonal influenza B continued to circulate.
  • In India, transmission of pandemic influenza virus remains active but stable in Kerala.
  • In Singapore, substantial co-circulation of pandemic and seasonal influenza H3N2 viruses was detected in May and June 2010.

Southern Hemisphere

  • In South Africa, a sharp increase in the levels of seasonal influenza (H3N2 and type B) viruses occurred in June.2
  • In New Zealand, ILI rates increased during June.
  • New Zealand has recorded its first death from pandemic (H1N1) 2009 influenza in 2010.
  • In Chile and Argentina, ILI rates remained low.

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.
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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 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 'Influenza Monthly Epidemiology Report, NSW'. This report is provided monthly. The New South Wales Influenza Surveillance Program collects data from 56 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 and 2010 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 15 sentinel hospitals across Australia. The data for this reporting period are sourced only from 11 hospitals and do not include NT.

Australian and New Zealand Intensive Care Society data (ANZICS data)

The Australian and New Zealand Intensive Care Society provides data from a `near real time` registry of patients admitted to Australian ICUs. This documents the key factors influencing mortality, as well as the need for hospitalisation and mechanical ventilation. Information collected includes person characteristics and information on relevant co-morbidities, nature of the clinical syndrome associated with pandemic (H1N1) 2009, major therapeutic interventions from which organ failure outcomes can be imputed, vaccination status and vital status at time of ICU discharge and hospital discharge.

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6. References

1 Chinese National Influenza Centre Influenza Weekly Report 20 June 2010. Available from: http://www.cnic.org.cn/eng/ Accessed 30 June 2010.
2 WHO Pandemic (H1N1) 2009 - Update 107 & Virological Surveillance Weekly Update. Available from http://www.who.int/csr/don/en/ Accessed 14 July 2010.