Influenza

Australian influenza report 2008 - Current report - 7 November 2008

The Australian Influenza Report is compiled from a number of data sources, including laboratory-confirmed notifications to NNDSS, sentinel influenza-like illness reporting from general practitioners and emergency departments, workplace absenteeism, and laboratory testing. It is produced fortnightly from May to October. A more in-depth end of season report is also published in Communicable Diseases Intelligence.

Report No. 12
Week ending 7 November 2008

A print friendly version of this report is available as a PDF (89 KB)

Prepared by the Vaccine Preventable Disease Surveillance Section

Disclaimer
The Australian Government Department of Health and Ageing makes every effort to ensure the quality of the information available in this report, however, no guarantees can be made regarding its accuracy, currency, completeness and relevance for various purposes.

This report is based on data available as at 10 November 2008. Delays in the reporting of data may cause data to change retrospectively. Data and information contained in this report should be cautiously interpreted. Any questions regarding the data, information or other contents should be directed to: epi@health.gov.au

This will be the final Australian Influenza Report produced for 2008.

Executive summary

Background

Influenza causes annual epidemics of respiratory disease. Influenza epidemics usually occur during the winter months in temperate climates, causing an increase in hospitalisations for pneumonia, exacerbation of chronic diseases and also contribute to increased mortality, particularly among the elderly and those with high risk underlying conditions. In tropical climates, influenza infection may have two annual peaks, as illustrated in the Northern Territory.

The start of the annual influenza season is usually first detected by increased presentations at General Practitioners (GPs) of ‘influenza-like illness’ (ILI) followed by increases in notifications of laboratory confirmed influenza.
Laboratory confirmed influenza is a notifiable condition in all jurisdictions in Australia and data are provided to the Department's National Notifiable Diseases Surveillance System (NNDSS). All NNDSS data included in this report are extracted by diagnosis date.

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Current status

• Laboratory-confirmed influenza notifications have continued to decrease during this reporting period (Figure 1). Nationally, notifications have returned to baseline levels however some states, particularly South Australia and the Northern Territory, have seen an increase in notifications in this reporting period.
• This year-to-date (YTD) (up to 7 November 2008) there have been 8,400 cases of influenza notified in Australia. During the same period in 2007, 10,188 cases of laboratory-confirmed influenza were reported.
• Approximately 43.2% of these cases have been in Queensland, 17.2% in New South Wales and 14.5% in Victoria. The notification rate per 100,000 population is highest in Queensland (86.8), followed by the Northern Territory (77.2), Tasmania (73.8) and the Australian Capital Territory (68.6).
• Notification rates are highest in children under one year of age. YTD the rate in males under one year is approximately 180 cases per 100,000 population and 140 cases per 100,000 for females under one year (Figure 3).
• During this reporting period, notifications were predominantly type A. During the season notifications were predominantly Type B (Figure 5).
• Presentations of ILI, defined as cough, fever and fatigue, to the Australian Sentinel Practices Research Network (ASPREN) general practitioners decreased and have almost returned to baseline levels during this reporting period (Figure 6).
• In the last fortnight, the WHO Collaborating Centre for Reference and Research in Influenza (WHOCC) has typed 108 samples of which 39 were A/Brisbane/59/2007-like, 49 were A/Brisbane/10/2007-like (two ‘low-reactor’), two were B/Florida/4/2006-like and 18 were B/Malaysia/2506/2004-like. YTD the WHOCC has typed 697 influenza samples.
• The Australian Paediatric Surveillance Unit (APSU) has completed reporting for 2008. Overall in 2008, a total of 43 cases of severe complications following influenza infection in children under 15 years of age who were admitted to Intensive Care Units (ICUs).

Laboratory confirmed influenza

There have been 8,400 cases of laboratory confirmed influenza diagnosed year-to-date (YTD) in 2008 (Figure 1). There were 10,188 influenza cases in the same period last year.

As influenza only became nationally notifiable in 2001, a 5 year rolling mean cannot be calculated for years prior to 2006.

Figure 1: Number of notifications of laboratory-confirmed influenza, NNDSS, Australia, 1 January 2003 to 7 November 2008, by week of diagnosis

Source: National Notifiable Diseases Surveillance System

Notifications in 2008 have been predominantly from Queensland, with 3,632 (43.2%) notifications year-to-date (Table 1; Figure 2). New South Wales had 1,447 cases (17.2%) of influenza notified and Victoria 1,219 cases (14.5%).
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Figure 2: Number of laboratory-confirmed influenza notifications, NNDSS, 1 January to 7 November 2008, by jurisdiction and week of diagnosis

Source: National Notifiable Diseases Surveillance System

National age-specific notification rates YTD show the highest rate of notifications occurred in children 0-4 years (Figure 3). In this group, rates are highest in children under 1 year old at approximately 180 cases per 100,000 for males and 140 per 100,000 for females (Figure 3 insert).

Figure 3: Notification rates of laboratory-confirmed influenza, NNDSS, Australia, 1 January to 7 November 2008, by age group and sex

Source: National Notifiable Diseases Surveillance System

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Antigenic characteristics

Year to date, 3,324 cases (39.9%) of influenza notifications to NNDSS have been Influenza type A, 4,513 cases (54.1%) have been Influenza Type B and 495 cases (6.0%) were untyped (Figure 4). Of the type A notifications that were subtyped, 180 were H3N2 and 20 were H1N1.

Figure 4: Typing characteristics of notifications of laboratory-confirmed influenza, Australia, NNDSS, 1 January 2008 to 7 November 2008

Source: National Notifiable Diseases Surveillance System

Overall in the 2008 season, influenza type B has been the predominant circulating seasonal influenza strain. There has not been a predominantly type B season in Australia since influenza became nationally notifiable in 2001. Strains circulating in the 2007/2008 Northern Hemisphere season were primarily type A (Figure 5).

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Figure 5: Typing characteristics of notifications of laboratory-confirmed influenza, Australia, 1 January 2003 to 7 November 2008, by week of diagnosis, NNDSS

Sentinel general practice surveillance

Data available from the Australian Sentinel Practices Research Network (ASPREN) show that ILI consultation rates decreased and have almost returned to baseline levels during this reporting period. The rate was approximately 9 ILI consultations per 1000 GP consultations in the week ending 2 November 2008 (Figure 6).

Figure 6: Rate of influenza-like illness reported from ASPREN from 1 January 2006 to 2 November 2008 by week

Source: Australian Sentinel Practice Research Network data

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Sentinel emergency department surveillance

The New South Wales Influenza Surveillance Program, which runs from May to October each year, has completed reporting for 2008. Overall, the trend in the rate of ILI consultations seen by NSW EDs in 2008 was delayed by approximately three weeks and was lower compared to the 2007 season (Figure 7).

Figure 7: Rate of influenza-like illness reported in New South Wales Emergency Departments from 1 May 2006 (wk 17 2006) to 17 October 2008 (wk 42 2008) by week

Source: NSW Health ‘NSW Influenza Surveillance Report’

Absenteeism surveillance

A national organisation provides data on the number of employees that have been on sick leave for a continuous period of more than three days. These data are not influenza or ILI specific and absenteeism may be a result of other illnesses.

Absenteeism rates in 2008 have been following the similar trends to those seen in 2006 (Figure 8). No data have been provided during this reporting period.

Figure 8: Absenteeism rates, 1 January 2006 to 30 July 2008, by week and NNDSS influenza notifications, Rate per 100,000 population, 1 January 2008 to 17 October 2008, by week

Source: NSW Health ‘NSW Influenza Surveillance Report’

International seasonal activity summary

The overall global influenza activity was low in weeks 43–44, with the WHO reporting sporadic or no activity in the northern hemisphere and a decline of activity in the Southern Hemisphere.¹

Many European countries reported sporadic or no influenza activity, with 42 isolates positive for influenza: 23 were type A (not subtyped); five type A(H1); 10 type A(H3) and four type B. These isolates were collected in Belgium, Denmark, England, Germany, Ireland, Norway and Poland. ²

In the fortnight ending 1 November 2008, sporadic influenza activity was reported in the USA. During this period, 16 isolates tested positive for influenza, of which 10 were type A (not subtyped), two type A(H1); one type A(H3) and three type B.³

Canada reported low levels of influenza activity in the fortnight ending 1 November 2008. Six isolates were positive for influenza of which five were type A and one was type B. Four of these isolates were further typed: one was A/Brisbane/59/2007-like (H1N1), two were B/Florida/4/2006-like and one was B/Malyasia/2506/2004-like. The A/Brisbane/59/2007-like (H1N1) isolate contained the H274Y mutation that confers oseltamivir resistance. ⁴

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Data considerations

NNSSS (National Notifiable Diseases Surveillance System)

NNDSS comprises of notifications from jurisdictions of laboratory-confirmed influenza cases. Influenza is notifiable in all jurisdictions in Australia. Data included in this report was extracted and analysed on 10 November 2008.

ASPREN

ASPREN has Sentinel GPs who report ILI in NSW, SA, ACT, Vic, Qld 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 2008 may be different to that of previous years.

ASPREN data is sent to the Surveillance Branch on a weekly basis, and is currently available up until 2 November 2008.

Sentinel Emergency Department (ED) data

NSW - ED surveillance data are extracted from the ‘NSW Influenza Surveillance Report’. This report is provided weekly and data are currently available up until 17 October 2008.

WA - ED surveillance data are extracted from the ‘EDSS News’ Report. This report is provided weekly and data are currently available up until 2 November 2008.

International summary - References

Seasonal influenza activity in the world, 7 November 2008, available from: http://www.who.int/csr/disease/influenza/update/en/index.html, accessed 10 November 2008.
2.EISS Weekly Electronic Bulletin Influenza Season 2008-2009 Week 43 & 44. Available from: http://www.eiss.org/cgi-files/bulletin_v2.cgi?season=2008. Accessed 10 November 2008.
3. CDC FluView 2008-2009 influenza season, weeks 43 & 44. Available from: http://www.cdc.gov/flu/weekly/ Accessed 10 November October 2008.
4. Flu Watch Weekly reports 2008-2009 season weeks 43 & 44. Available from: http://www.phac-aspc.gc.ca/fluwatch/08-09/index-eng.php accessed 10 November 2008.