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2019 Season Summary - May 2020

Public Health Services produce the fluTAS Report to provide information about the level of influenza (flu) in Tasmania. Multiple surveillance data sources are used to obtain measures of influenza activity in the community.

This surveillance report provides a summary of influenza activity in Tasmania during the period 1 January to 31 December 2019.

2019 Season Summary

• Like the national influenza season, the 2019 influenza season in Tasmania was characterised by an early start and an extended season with multiple peaks.
• There were 3 137 laboratory-confirmed influenza notifications received in 2019 corresponding to a rate of 593 notifications per 100 000 persons.
• Annual notifications were higher than in previous years (5-year average 2014-2018, 1 425 notifications), with the exception of 2017 (3 509 notifications).
• Influenza testing during 2019 (15 875 tests) was 2.2 times the amount of testing conducted during 2018 (7 081tests).
• The weekly proportion of tests positive for influenza peaked to 27 per cent during April and to 28 per cent during August.
• Annual notification rates were highest in those aged 75 years and older (875 notifications per 100 000 population), followed by children aged 0 to 4 years (709 notifications per 100 000) and adults aged 25-29 (699 notifications per 100 000).
• 235 patients were admitted to the Royal Hobart Hospital with laboratory-confirmed influenza between 1 April and 4 October 2019.

Influenza activity

Annual seasonal influenza infection is unpredictable and varies from season to season. Severity of an influenza season is related to many factors including the influenza strains and subtypes that are circulating, the population groups most affected, the susceptibility of the population, and changes that may occur to the viruses during the year. Our surveillance systems at a state and national level help us to understand influenza activity and severity.

The 2019 influenza season both nationally and in Tasmania was characterised by an early start, and an extended season with multiple peaks.

Notifications of laboratory-confirmed influenza to Public Health Services

Influenza notifications are based on positive laboratory tests. Many people with influenza-like illness choose not to attend medical care or are not tested when they attend. As a result, notifications represent a small proportion of the total influenza cases in the community.

There were 3 137 laboratory-confirmed influenza notifications received in 2019 corresponding to a rate of 593 notifications per 100 000 persons (Figure 1). High influenza activity was observed between January and March with 291 notifications compared to the 5-year average (2014-2018) of 67. This high activity extended into autumn and early winter with 1 637 notifications between April and July compared to the 5-year average of 215. As shown in Figure 2, annual notifications were higher than in previous years (5-year average 2014-2018, 1 425 notifications), except for 2017 (3 509 notifications).

Figure 1: Notifications of influenza in Tasmania, by week, 1 January 2015 to 31 December 2019.

Figure 2: Notifications of influenza in Tasmania, by week, for 2019 compared to the 5-year mean 2014-2018.

Geographical distribution of activity

Between 1 January and 31 December 2019 there were 1 983 cases in the South, 820 cases in the North and 329 cases in the North-West (Figure 3). Notification rates per 100 000 persons were 731 for the South, 565 for the North and 294 for the North-West. Five visitors to the state were diagnosed with influenza in Tasmania during 2019.

Figure 3: Weekly notifications of influenza in Tasmania, by region, 1 January to 31 December 2019.

Influenza testing

Since the start of 2019 influenza testing conducted by Tasmanian laboratories was significantly greater than previous years. Between 1 January and 31 December 2019, a total of15 875influenza Polymerase Chain Reaction (PCR) tests were reported by laboratories, 2.2 times the testing conducted during the same period of 2018 (7 081 tests).

Proportion of tests positive for influenza

As shown in Figure 4, the weekly proportion of tests positive for influenza peaked during April (week 16) to 27 per cent and to 28 per cent in August (week 33). On average, 19 per cent of weekly influenza tests were positive during April to October (range 8 per cent to 28 per cent).

Figure 4: Influenza PCR testing in Tasmania, by week, from 1 January to 31 December 2019.

Virology

The majority of confirmed influenza cases reported during 2019 were influenza A (88 per cent). A small proportion of influenza A viruses undergo further subtyping. The most commonly reported subtype during 2019 was influenza A(H3N2) (82 per cent). The H3N2 strain is associated with greater morbidity and mortality in older adults.

Table 1. Notifications of influenza in Tasmania by subtype and month, 1 January to 31 December 2019.

At-risk populations

During 2019, overall notification rates were highest in those aged 75 years and older (875 notifications per 100 000 population), followed by children aged 0 to 4 years (709 notifications per 100 000) and adults aged 25 to 29 (699 notifications per 100 000). Influenza A accounted for the greatest number of notifications across all age groups. Notification rates for influenza A were highest in adults aged 75 years and older (868 notifications per 100 000), children aged 0 to 4 years (618 notifications per 100 000) and adults aged 25 to 29 years (612 notifications per 100 000). Notification rates for influenza B were highest in children aged 5 to 9 years (187 notifications per 100 000).

Figure 5. Notification rates and total number of notifications of laboratory confirmed influenza in Tasmania, 1 January to 31 December 2019, by age group.

Other circulating respiratory illness

Many viruses cause the ‘common cold’ and ‘influenza-like illnesses’. The Royal Hobart Hospital (RHH) laboratory performs a PCR test that detects influenza A and B viruses, as well as seven other respiratory pathogens commonly associated with respiratory illness. Most individuals tested were from emergency department presentations and hospitalised patients to the RHH.

FluTAS reports on influenza A, influenza B, and seven other respiratory viruses most commonly reported in Tasmania. Overall, 5 850 people were tested in 2019, compared to 2 351 in 2018. The most commonly detected respiratory pathogens during 2019 were Rhinovirus (33 per cent), Respiratory Syncytial Virus (RSV) (14 per cent) and Parainfluenza viruses (11 per cent).

Influenza Severity

FluCAN (Influenza cases admitted to hospital)

The Influenza Complications Alert Network (FluCAN) reports on influenza-related hospitalisations and complications in sentinel hospitals Australia-wide during each influenza season. This system aims to provide an indication of severity of the influenza season and identify groups at higher risk of influenza-related hospital admission. The details of recent FluCAN activity are published in the Australian Influenza Surveillance Report available at www1.health.gov.au/internet/main/publishing.nsf/Content/cda-surveil-ozflu-flucurr.htm#current. The Royal Hobart Hospital participates in FluCAN.

Seasonal sentinel hospital surveillance began in Australia on 1 April 2019. At 18 October, 4 053 hospital admissions of laboratory-confirmed influenza were reported nationwide. Of these, 260 patients (six per cent) were admitted to an intensive care unit. In Tasmania, 237 patients were admitted to the Royal Hobart Hospital with 9 patients (four per cent) admitted to the intensive care unit.

Influenza-like illness

FluTracking (Community Syndromic Surveillance)

FluTracking is a national, weekly online survey that asks participants to report whether they have had fever and/or cough in the preceding week. FluTracking information is available at flutracking website and on Facebook - Flutracking

FluTracking recommenced on Monday 8 April 2019, three weeks earlier than usual due to increased influenza activity across Australia. Nationally, participation in FluTracking increased by 16 per cent from 2018 to 52 768 participants in 2019. Overall, 4 279 Tasmanians completed at least one survey in 2019, an average of 3 750 Tasmanians each week. This was an increase on 2018 participation involving an average of 3 150 Tasmanians per week.

Figure 6. Percentage of FluTracking participants in Tasmania reporting fever and cough compared to number of influenza notifications, week ending 28 September 2019.

ASPREN (General Practice Syndromic Surveillance)

The Australian Sentinel Practices Research Network (ASPREN) includes registered sentinel General Practices (GPs) across Australia who report fortnightly on the number of patients presenting with influenza-like illness (ILI). Five GPs participate in Tasmania. ASPREN is a joint initiative of the Royal Australian College of General Practitioners and the University of Adelaide. Further information is available on the aspren website

For the fortnight ending Sunday 8 September 2019, ASPREN reported that in Tasmania, the average level of ILI activity was less-than 25 out of 1 000 consultations. This was categorised by ASPREN as ‘normal’ activity (1-5 out of 1 000 consultations is categorised as “baseline”, 25 – 39 out of 1 000 consultations is categorised as “high activity”).

Annual Influenza Vaccine

Composition of 2019 influenza vaccines

The annual influenza vaccine is reviewed late each year, aiming to produce vaccines for the following year that provide protection from influenza strains likely to be common during winter. Advice on the formulation of annual influenza vaccines is provided to the Therapeutic Goods Administration (TGA) by the Australian Influenza Vaccine Committee (AIVC). The influenza virus strains included in the 2019 seasonal influenza vaccines in Australia were:

• * A/Michigan/45/2015, (H1N1)pdm09-like virus;
• * A/Switzerland/8060/2017, (H3N2)-like virus; and
• * B/Phuket/3073/2013-like virus, Yamagata lineage.
• * B/Colorado/06/2017-like virus, Victoria lineage.

Further information on the composition of influenza vaccines is available on the Australian Government's TGA website.

Further Information

View the latest information on influenza in Tasmania

Past FluTAS reports are available on the Communicable Diseases Prevention Unit webpage