Surveillance Report
No. 6, 2015, REPORTING PERIOD:
1 August to 14 August 2015 /
The Department of Health acknowledges the providers of the many sources of data used in this report and greatly appreciates their contribution.
SUMMARY
· Influenza activity continued to increase nationally this fortnight. All jurisdictions with the exception of Western Australia are continuing to increase in activity.
· Influenza notification rates have been highest among those aged between 5 and 9 and over 85 years with a secondary peak in those aged 40-44 years.
· Influenza B continues to be the dominant influenza virus type nationally, comprising two thirds of all notifications. In South Australia, Victoria and Western Australia, the proportion of influenza A has increased.
· All systems that monitor influenza-like illness (ILI) activity are reporting increasing activity while remaining within the range of previous seasons. Influenza is the primary cause of ILI in the community this fortnight.
· Hospitalisations with confirmed influenza increased in the past fortnight. While less severe overall, presentations appear to be more severe in children this year, with 11% of children presenting to sentinel hospitals with influenza admitted directly to ICU compared with 6% of adults.
· The seasonal influenza vaccines appear to be a good match for circulating strains. However approximately one-quarter of influenza B viruses tested are due to the lineage not contained in the trivalent seasonal vaccine (TIV). The mis-match compared to the TIV is most evident in Queensland and New South Wales.
Figure 1. Notifications of laboratory confirmed influenza, Australia, 1 January 2011 to 14 August 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 14 August 2015, influenza activity was reported as stable or increasing across all regions except metropolitan Perth where activity has started to decline. The geographic spread of influenza activity reported by state and territory health departments was ‘localised’ in the tropical region Queensland (Qld);‘regional’ in the Top End region of the Northern Territory (NT) and the Pilbara/Kimberley and southern regional areas of Western Australia (WA); and ‘widespread’ in all other areas (Figure 2). Many regions have reported recent increases in the proportion of laboratory tests which are positive for influenza. ILI activity reported from syndromic surveillance systems was unchanged compared with the previous reporting period in WA and increasing in all other regions.
Figure 2. Map of influenza activity by state and territory, Australia, 1 August to 14 August 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 the seasonal rise in rates of ILI among participants commenced in early August and is within range of recent years except 2012. ILI rates in the most recent fortnight have increased and are towards the upper range of recent seasons (Figure 3). In the week ending 16 August 2015, rates of fever and cough increased to 4.1% of all participants (3.5% of vaccinated participants and 4.8% of unvaccinated participants), up from 3.3% of all participants at the end of the previous fortnight. Fever, cough and absence from normal duties were reported by 2.9% of all participants (2.3% of vaccinated participants and 3.5% of unvaccinated participants)[1]. In the week ending 16 August 2015, 62.6% of participants reported having received the 2015 influenza vaccine. Of the 3,798 participants who identified as working face-to-face with patients, 2,990 (81%) 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
Sentinel General Practice Surveillance
Systems that measure ILI presentations to general practitioners indicated that the seasonal rise in ILI, which commenced in early May, has continued. During the reporting fortnight, the ILI rate was similar to the peak rate of recent years (Figure 4). In the fortnight ending 16 August 2015, the ILI consultation rate increased considerably to 16.7 notifications of ILI per 1,000 consultations, up from 13.7 in the previous fortnight.
Figure 4. Rate of ILI reported from sentinel GP surveillance systems, Australia, 1January2011 to 16 August 2015, by week.
SOURCE: ASPREN and VIDRL[2] GP surveillance systems.
In the fortnight ending 16 August 2015, specimens were collected from around 50% of Australian Sentinel Practices Research Network (ASPREN) general practitioner ILI patients. Of these patients, 50.5% were positive for influenza, a marked increase from 37% on the previous fortnight. Influenza B viruses were the predominant influenza subtype identified (Figure 5 and Table 1). The proportion of ILI patients positive for other respiratory viruses reduced considerably from 34% the previous fortnight to 20% this period. Rhinovirus continued to be the most common non-influenza virus detected.
Table 1. ASPREN laboratory respiratory viral test results of ILI consultations, 1 January to 16 August July 2015.
Fortnight(3 August– 16 August 2015) / YTD
(1 January – 16 August 2015)
Total specimens tested / 216 / 1854
Total Influenza Positive (%) / 50.5 / 25.1
Influenza A (%) / 15.7 / 8.1
A (H1N1) pdm09 (%) / 0.9 / 0.9
A (H3N2) (%) / 2.8 / 3.5
A (unsubtyped) (%) / 12.0 / 3.8
Influenza B (%) / 34.7 / 17.0
Other Resp. Viruses (%)* / 20.4 / 36.7
* Other respiratory viruses include human metapneumovirus, RSV, parainfluenza, adenovirus and rhinovirus.
Figure 5. Proportion of respiratory viral tests positive for influenza in ASPREN ILI patients and ASPREN ILI consultatio
SOURCE: ASPREN and WA SPN
Sentinel Emergency Department Surveillance
Western Australia Emergency Departments[3]
Viral respiratory presentations to WA emergency departments have plateaued at 58 per 1,000 ED presentations. This is a decline from a peak of 66 respiratory presentations per 1,000 ED presentations in the week ending 28 July. The current rates of presentations are within the range of recent seasons and less than the peak observed in 2012, a moderately severe season (Figure 6).
Figure 6. Rate of respiratory viral presentations to Western Australia emergency departments, 1January2011 to 16 August 2015, by week.
Source: WA Department of Health
New South Wales Emergency Departments
In the week ending 16 August 2015, the proportion of ILI presentations to all New South Wales (NSW) emergency departments increased to moderate (3.6 per 1000 presentations). ILI presentations have continued to increase and were within the range of activity seen in recent years (Figure7). ILI and pneumonia admissions to critical care decreased from the previous reporting period and were within the usual range 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 50.3 which is considerably higher than the previous fortnight. The index crossed the threshold of 15 on 26 June.
Figure 7. 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
The rate of ILI presentations to NT emergency departments increased slightly this reporting fortnight and within the usual range for this time of year (Figure 8).
Figure 8. Rate of influenza-like illness presentations to Northern Territory emergency departments, 1January2011 to 7 August 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 14 August, there were 39,137 laboratory confirmed notifications of influenza: 11,802 in Qld; 9,500 in NSW; 7,064 South Australia (SA); 6,278 in Victoria (Vic); 3,202 in WA; 683 in the Australian Capital Territory (ACT); 446 in Tasmania (Tas) and 162 in NT (Figure 9). Notification data for Vic are incomplete for the reporting period.
In the fortnight ending 14 August 2015, there were 11,796 notifications reported to the NNDSS (Figure 9). The three jurisdictions with the highest number of influenza notifications, Qld (4,379), NSW (3,551) and SA (1,989) together contributed 84% of notifications this fortnight, followed by Vic (1,005), WA (539), ACT (162), Tas 132), and NT (39). Victoria continues to experience high numbers of notifications, resulting in an administrative backlog; therefore notifications for the most recent week are likely to increase in future reports.
In recent weeks, trends in influenza notifications have varied across jurisdictions, with notifications generally stable or gradually increasing (Figure10). These data suggest that the season may be close to peaking in some areas but continuing to increase in others.
Figure 9. Notifications of laboratory confirmed influenza, Australia, 1 January to 14 August 2015, by state or territory and week.
Source: NNDSS
Figure 10. Notifications of laboratory confirmed influenza, 1 January to 14 August 2015, by state or territory and week.
* Victoria is currently experiencing high numbers of notifications, resulting in an administrative backlog; therefore notifications for the most recent week are likely to increase in future reports
Source: NNDSS
So far in 2015, notification rates have been highest among those aged 5-9 years and over 85 years with a secondary peak in those aged 35-44 years (Figure 11). This age distribution is driven by influenza B infections being prevalent in school aged children and influenza A(H3N2) and B affecting older age groups.
Figure 11. Rate of notifications of laboratory confirmed influenza, 1 January to 14 August 2015, by subtype and age group.
Source: NNDSS
Of the 11,796 influenza notifications reported to the NNDSS this reporting period, 68% were influenza B, 31% were influenza A (24% A(unsubtyped), 5% A(H3N2) and 2% A(H1N1)pdm09) and less than 1% were influenza A&B co-infections, influenza C or were untyped (Figure 12).
Influenza B was the dominant circulating strain in all jurisdictions this fortnight, except Tas where influenza A is dominant and overall activity remains low. Influenza B, as a proportion of all notifications, appears to be stabilising or decreasing in most jurisdictions, with influenza A increasingly reported particularly in SA, Vic and WA.
For the calendar year to 14 August 2015, 58% of cases were reported as influenza B and 41% influenza A (33% A(unsubtyped), 7% A(H3N2) and 1% A(H1N1)pdm09). Less than 1% were reported as either influenza A&B co-infections, influenza C or were untyped (Figure 12).
Figure 12. Notifications of laboratory confirmed influenza, Australia, 1 January to 14 August 2015, by subtype and week.
Source: NNDSS
Institutional influenza outbreaks
For the year to 3 August, there have been 80 laboratory-confirmed influenza outbreaks in institutions reported (Table 2), with all but one occurring in residential care facilities primarily housing aged persons. The outbreaks were caused by influenza A(H3N2) (20%), influenza A(H1N1)pdm09 (1% ), influenza A(unsubtyped) (53%), influenza B (20%) or a combination of types (6%). The high prevalence of institutional outbreaks caused by influenza A(H3N2) – noting that most of the “A(unsubtyped)” outbreaks are also likely to be A(H3N2) - reflects the higher incidence in the elderly of influenza A(H3N2) infection, relative to influenza B and A(H1N1)pdm09, as shown in Figure 11.
Table 2. Laboratory confirmed influenza outbreaks in institutions reported to the Commonwealth, 1 January 2014 to 3 August 2015, by state or territory*.
Year / ACT / NSW / NT / Qld / SA / Tas / Vic / WA2015 (Year to date) / 2 / 23 / 0 / 2 / 23 / 0 / 27 / 3
2014 (Total) / 6 / 120 / 0 / 10 / 27 / 0 / 51 / 6
* Notes on interpreting outbreak data:
Notification and reporting practices for institutional outbreaks vary by jurisdiction and impact outbreak ascertainment. The number of influenza associated outbreaks subsequently reported to the Commonwealth is therefore an under-estimate of the true incidence. The degree of under-representation is unknown and is most likely variable by jurisdiction. Outbreak data will be reported monthly during the influenza season.
Sentinel Laboratory Surveillance
Results from sentinel laboratory surveillance systems show that, in this reporting fortnight, influenza viruses were the major cause of influenza-like illness across all sites. Overall, 23% of the respiratory viral tests conducted over this period were positive for influenza, which is an increase of 5% from the previous fortnight (Table 3). Influenza B was the most common influenza type reported this fortnight for NSW and WA while influenza A was predominant in Vic and Tas. For the influenza A viruses for which subtyping data was available, the proportion of A(H3N2) continues to greatly exceed that of A(H1N1)pdm09 (Figure 13), which is consistent with laboratory confirmed notification data (Figure12).
Table 3. Sentinel laboratory respiratory virus testing results, 1 August to 14 August 2015.
NSW NIC / WA NIC / VIC NIC / TAS(PCR testing data)
Total specimens tested / 795 / 1534 / 199 / 431
Total influenza positive / 128 / 351 / 85 / 104
Positive influenza A / 54 / 139 / 61 / 80
A(H1N1)pdm09 / 4 / 14 / 2 / 2
A(H3N2) / 12 / 121 / 59 / 40
A(unsubtyped) / 38 / 4 / 0 / 38
Positive influenza B / 75 / 212 / 24 / 24
Positive influenza A&B / 0 / 0 / 0 / 0
Proportion Influenza Positive (%) / 16.1% / 22.9% / 42.7% / 24.1%
Most common respiratory virus detected / Influenza B Virus / Influenza B Virus / Influenza A Virus / Influenza A Virus
Source: National Influenza Centres (WA, NSW and Vic) and Tasmanian public hospital laboratory PCR testing