Australian Influenza

/

Australian Influenza

Surveillance Report

No. 4, 2015, REPORTING PERIOD:
4 July to 17 July 2015 /

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

SUMMARY

·  Most surveillance systems indicate that the influenza season is well underway. It is not an unusual influenza season thus far.

·  All States and Territories, with the exception of the Northern Territory, have shown increases in influenza activity in recent weeks.

·  Influenza notification rates have been highest among those aged over 85 years with a secondary peaks in those aged 5-9 and 40-44 years.

·  In the last fortnight, influenza B has been the dominant influenza virus type, comprising two thirds of all notifications.

·  Hospitalisations with confirmed influenza have increased in recent weeks in line with the seasonal increase in activity. Presentations to hospital appear to be less severe in adults, with the proportion of adult patients admitted to ICU less than the proportion reported in previous years.

·  All systems that monitor influenza-like illness (ILI) activity are reporting activity within the range observed in recent seasons. ILI in the community continues to be driven by other non-influenza respiratory viruses, in particular RSV and Rhinovirus.

·  The seasonal influenza vaccines appear to be a good match for circulating strains.

Figure 1. Notifications of laboratory confirmed influenza, Australia, 1 January 2011 to 17 July 2015, by week.

Source: NNDSS

KEY INDICATORS

Influenza activity and severity in the community are 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 (NNDSS);
·  influenza associated hospitalisations;
·  emergency department (ED) presentations for influenza-like illness (ILI);
·  general practitioner (GP) consultations for ILI;
·  ILI-related call centre calls and community level surveys of ILI; and
·  sentinel laboratory test results.
How severe is the disease, and is severity changing? / Indicated by trends in:
·  hospitalisations, intensive care unit (ICU) admissions and deaths; and
·  clinical severity in hospitalised cases and ICU admissions.
Is the virus changing? / Indicated by trends in:
·  drug resistance; and
·  antigenic drift or shift of the circulating viruses.

1. Geographic Spread of Influenza Activity in Australia

In the fortnight ending 17 July 2015, influenza activity was reported as stable or increasing across all regions for which reports were received. The geographic spread of influenza activity reported by state and territory health departments was ‘sporadic’ in the tropical region of Queensland (Qld); ‘localised’ in the Pilbara/Kimberley and southern regional areas of Western Australia (WA); ‘regional’ in the southern and central regions of Qld, New South Wales (NSW) and Victoria (Vic) and ‘widespread’ in the Australian Capital Territory (ACT), Tasmania (Tas) and South Australia (SA) (Figure 2). ILI activity reported from syndromic surveillance systems was unchanged compared with the previous reporting period in WA and Tas and increasing in all other regions for which reports were received. No report was received for the Northern Territory (NT) for this reporting period.

Figure 2. Map of influenza activity by state and territory, Australia, 4 July to 17 July 2015.

2. Influenza-like Illness Activity

Community Level Surveillance

FluTracking

FluTracking, a national online system for collecting data on ILI in the community, indicated that rates of ILI among participants so far this year have been low and within the range of recent seasons (Figure 3). In the week ending 19 July 2015, rates of fever and cough decreased slightly to 2.7% of all participants (2.4% of vaccinated participants and 2.9% of unvaccinated participants). Fever, cough and absence from normal duties were reported by 1.6% of all participants (1.5% of vaccinated participants and 1.6% of unvaccinated participants)[1]. In the week ending 19 July 2015, 62.1% of participants reported having received the 2015 influenza vaccine. Of the 3,781 participants who identified as working face-to-face with patients, 3,054 (80.8%) have received the vaccine.

Figure 3. Proportion of fever and cough among FluTracking participants, Australia, between May and October, 2011 to2015, by week.

Source: FluTracking1

National Health Call Centre Network

ILI related calls to the National Health Call Centre Network (NHCCN) have been steadily increasing since the beginning of the year. The proportion of ILI related calls to the NHCCN are currently tracking slightly higher than 2014, but within the range observed in recent seasons(Figure 4).

Figure 4. Number of calls to the NHCCN related to ILI and percentage of total calls, Australia, 1January2011 to 17 July 2015, by week.

Note: NHCCN data do not include Queensland and Victoria

Source: NHCCN

Sentinel General Practice Surveillance

In the fortnight ending 19 July 2015, the overall trend in the sentinel general practitioner ILI consultation rate continued to increase to 10.8 notifications of ILI per 1,000 consultations. The rate of ILI consultations has increased in recent weeks, yet remains lower than the peak of most previous seasons (Figure5).

Figure 5. Weekly rate of ILI reported from GP ILI surveillance systems, Australia, 1January2011 to 19 July 2015, by week.

SOURCE: ASPREN and VIDRL[2] GP surveillance systems.

In the fortnight ending 19 July 2015, specimens were collected from around 68% of Australian Sentinel Practices Research Network (ASPREN) general practitioner ILI patients. Of these patients, 28% were positive for influenza. Influenza B viruses were the predominant influenza subtype idenitifed (Figure 6 and Table 1). The proportion of ILI patients positive for other respiratory viruses remained elevated at 37%. Rhinovirus was the most common non-influenza virus detected.

Table 1. ASPREN laboratory respiratory viral test results of ILI consultations, 1 January to 19 July 2015.

Fortnight
(5 July– 19 July 2015) / YTD
(1 January – 19 July 2015)
Total specimens tested / 203 / 1264
Total Influenza Positive (%) / 27.6 / 17.9
Influenza A (%) / 8.4 / 6.2
A (H1N1) pdm09 (%) / 0.5 / 0.6
A (H3N2) (%) / 2.5 / 2.6
A (unsubtyped) (%) / 5.4 / 3.0
Influenza B (%) / 19.2 / 11.7
Other Resp. Viruses (%)* / 37.4 / 33.5

* Other respiratory viruses include human metapneumovirus, RSV, parainfluenza, adenovirus and rhinovirus.

Figure 6. Proportion of respiratory viral tests positive for influenza in ASPREN ILI patients and ASPREN ILI consultation rate, Australia, 1January to 19 July 2015, by week.

SOURCE: ASPREN and WA SPN

Sentinel Emergency Department Surveillance

Western Australia Emergency Departments[3]

Viral respiratory presentations to WA emergency departments decreased both weeks in this fortnight. The current rates of presentations are within the range of recent seasons but remain below the peak observed in 2012, a moderately severe season (Figure 7).

Figure 7. Rate of respiratory viral presentations to Western Australia emergency departments, 1January2011 to 19 July 2015, by week.

Source: WA Department of Health

New South Wales Emergency Departments

In the week ending 19 July 2015, the proportion of ILI presentations to all NSW emergency departments increased but remained low at 1.9 per 1,000 presentations which was within the usual range of activity for this time of year (Figure8). ILI and pneumonia admissions to critical care wards decreased this week but were above the usual range seen for this time of year.

The NSW emergency department surveillance system uses a statistic called the ‘index of increase’ to indicate when ILI presentations are increasing at a statistically significant rate. An index value greater than 15 suggests that influenza is circulating widely in the NSW community. The index of increase for ILI presentations increased to 26.2 from 18.6 on 15 July, consistent with the influenza season having started in late June.

Figure 8. Rate of influenza-like illness presentations to New South Wales emergency departments, between May and October, 2011 to 2015, by week.

Source: ‘NSW Health Influenza Surveillance Report’4

Northern Territory Emergency Departments

During the current reporting period, the overall rate of ILI presentations to NT emergency departments was steady and remains within the usual range for this time of year (Figure 9).

Figure 9. Rate of influenza-like illness presentations to Northern Territory emergency departments, 1January2011 to 18 July 2015, by week.

Source: Centre for Disease Control, Department of Health, Northern Territory Government

3. Laboratory Confirmed Influenza Activity

Notifications of Influenza to Health Departments

For the year to 17 July, there were 19,075 laboratory confirmed notifications of influenza: 5,129 in Qld; 3,811

in NSW; 3,692 SA; 3,604 in Victoria; 2,114 in WA; 391 in the ACT; 236 in the Tas and 98 in NT (Figure 10).

In the fortnight ending 17 July 2015 there were 4,045 notifications reported to the NNDSS (Figure 10). The three jurisdictions with the highest number of influenza notifications, Qld (1,006), Vic (885) and SA (812) together contributed 67% of notifications this fortnight, followed by NSW (753), WA (383), ACT (139), Tas (57), and NT (10). In recent weeks, influenza notifications have been increasing across all jurisdictions, except the NT, in line with the expected seasonal increase in influenza activity (Figure11).

Figure 10. Notifications of laboratory confirmed influenza, Australia, 1 January to 17 July 2015, by state or territory and week.

Source: NNDSS

Figure 11. Notifications of laboratory confirmed influenza, 1 January to 17 July 2015, by state or territory and week.

Source: NNDSS

So far in 2015, notification rates have been highest among those aged over 85 years with a secondary peaks in those aged 5-9 and 40-44 years (Figure 12). This age distribution trend is consistent with influenza B infections being prevalent in school aged children and influenza A affecting older age groups.

Figure 12. Rate of notifications of laboratory confirmed influenza, 1 January to 17 July 2015, by subtype and age group.

Source: NNDSS

Of the 4,045 influenza notifications reported to the NNDSS this reporting period, 66% were influenza B, 34% were influenza A (29% A(unsubtyped), 4% A(H3N2) and 1% A(H1N1)pdm09) and less than 1% were influenza A&B co-infections, influenza C or were untyped (Figure 13).

The distribution of the influenza virus types and subtypes has been variable between jurisdictions this reporting fortnight. Influenza B was the dominating circulating strain in all jurisdictions, except Tas and the ACT where overall activity remains low.

For the calendar year to 17 July 2015, 51% of cases were reported as influenza A (40% A(unsubtyped), 9% A(H3N2) and 2% A(H1N1)pdm09) and 48% were influenza B. Less than 1% were reported as either influenza A&B co-infections, influenza C or were untyped (Figure 13).

Figure 13. Notifications of laboratory confirmed influenza, Australia, 1 January to 17 July 2015, by subtype and week.

Source: NNDSS

Sentinel Laboratory Surveillance

Results from sentinel laboratory surveillance systems show that Respiratory Syncytial Virus and influenza virus were major causes of influenza-like illness this reporting fortnight. Overall, 18% of the respiratory viral tests conducted over this period were positive for influenza, an increase from 13% reported the previous fortnight (Table 2). Influenza B was the most common influenza type reported this fortnight. For the influenza A viruses for which subtyping data was available, the proportion of A(H3N2) continues to exceeded that of A(H1N1)pdm09, which is consistent with laboratory confirmed notification data (Figure14).

Table 2. Sentinel laboratory respiratory virus testing results, 4 July to 17 July 2015.

NSW NIC / WA NIC / VIC NIC / TAS
(PCR testing data)
Total specimens tested / 636 / 1172 / 207 / 150
Total influenza positive / 67 / 249 / 31 / 47
Positive influenza A / 34 / 75 / 11 / 31
A(H1N1)pdm09 / 1 / 9 / 1 / 1
A(H3N2) / 7 / 66 / 8 / 15
A(unsubtyped) / 26 / 0 / 2 / 16
Positive influenza B / 33 / 174 / 20 / 16
Positive influenza A&B / 0 / 0 / 0 / 0
Proportion Influenza Positive (%) / 10.5% / 21.2% / 15.0% / 31.3%
Most common respiratory virus detected / RSV / RSV / Influenza B Virus / RSV

Source: National Influenza Centres (WA, NSW and Vic) and Tasmanian public hospital laboratory PCR testing

Figure 14. Proportion of sentinel laboratory tests positive for influenza 4 July to 17 July 2015, by subtype and fortnight.

Source: National Influenza Centres (WA, Vic, NSW) and Tasmanian laboratories (PCR testing)

Hospitalisations

Influenza Complications Alert Network (FluCAN)

In the last fortnight, the Influenza Complications Alert Network (FluCAN) sentinel hospital surveillance system reported 127 admissions with confirmed influenza, a 42% increase on the admissions reported in the previous fortnight. Since 1 April 2015, 8.2% of influenza patients have been admitted directly to ICU and the majority of overall influenza admissions have been due to influenza B infection (54%) (Figure 15). Case counts this year are similar to numbers seen in 2012 and 2014, and greater than those reported in 2011 and 2013. Around 42% of the cases are aged 65 years or older and 73% of all cases had significant risk factors present on admission. A higher proportion of children (12/60; 20%) have been admitted directly to ICU compared with adults (5.8%). The proportion of adult patients admitted to ICU is less than reported in previous years.

Figure 15. Number of influenza hospitalisations at sentinel hospitals, 1 April to 17 July 2015, by week and influenza subtype.

Source: FluCAN Sentinel Hospitals

Queensland Public Hospital Admissions (EpiLog)

Admissions to public hospitals in Queensland with confirmed influenza are detected through the EpiLog system. Up to 19 July 2015, there were 326 admissions, including 30 to intensive care units (Figure 16). The majority of hospital admissions have been associated with influenza B infections (61%), and of those influenza A infections that have been subtyped, these have mostly been A(H3N2)[4]. In the year to date, there is a broad age distribution of influenza-associated hospitalisations with high numbers in the 0-9 and over 50 year age group. The median age of hospitalised cases is 50 years with a range of less than one to 94 years.