DEATHS DUE TO INFLUENZA, 2017

In 2017 there were 1,255 deaths due to influenza, recording a standardised death rate of 3.9 per 100,000 persons. This is a significant increase from 2016 where 464 influenza deaths were recorded. An individual dying from influenza in 2017 was most likely to be female, aged over 75 years, have multiple co-morbidities and living in the eastern states of Australia.

What is Influenza?

Influenza is a contagious respiratory infection caused by a virus. It is easily spread from person to person through methods such as coughing or sneezing and is often seasonal, occurring in winter months in Australia (Department of Health, 2015). There are 3 types of influenza virus which affect people (influenza A, B and C), but only A and B cause serious outbreak and disease. The National Influenza Surveillance Scheme (NISS) confirmed that influenza A was the most common strain of virus identified in 2017 (NISS, 2017). Persons with weakened immune systems, who are elderly, and who have other existing chronic health conditions are at greater risk of contracting and developing a severe case of influenza.

Laboratory confirmed Influenza is a notifiable disease in Australia. The NISS coordinates information during "flu season" from a number of sources, with a focus on understanding and reporting severity of disease, virology and incidence. In 2017, approximately two thirds of deaths due to influenza (806 deaths) were certified with an identified seasonal virus. The remaining deaths (449) did not have a viral strain identified on the death certificate.

Links to pneumonia

Influenza and pneumonia are often reported together, however they are two different diseases. While influenza is a viral respiratory tract infection, pneumonia is an infection or inflammation of the lungs which can be caused by bacteria, fungi or a virus. Influenza is a common cause of pneumonia and in 2017 there were 563 influenza deaths where pneumonia was also certified on the death certificate as having developed and contributed to death.

When grouped together, influenza and pneumonia accounted for 4,269 deaths, and were the 9^th leading cause of death, moving from the 11^th leading cause of death in 2016 (3,334 deaths). The majority of the increase was driven by the influenza virus (84.6%).

Age and Sex

Females experienced a slightly higher rate of influenza deaths in 2017 with 6.0 deaths per 100,000 capita being recorded (744 deaths) compared with 4.2 per 100,000 persons for males (511 deaths).

From age 70 numbers of deaths increased progressively. The age group with the highest number of deaths was 90-94 years with 312 deaths recorded. This aligns with evidence from the Department of Health reporting that the elderly were most susceptible to the influenza strain in 2017 (NISS, 2017).

For both males and females, the highest rate of influenza death occurred in those aged over 95 years, with 454.7 and 409.9 deaths per 100,000 persons recorded respectively.


Influenza deaths (J09-J11) - number and age-specific death rate by sex, 2017 (a)(b)

Influenza deaths (J09-J11)	No. of Male deaths	No. of Female deaths	Total	Rate of Males	Rate of Females	Total
0-44 Years	10	11	21	0.1	0.2	0.1
45 Years - 64 Years	33	25	58	1.1	0.8	1.0
65 Years - 69 Years	30	24	54	5.1	4.0	4.5
70 Years - 74 Years	39	25	64	8.3	5.1	6.7
75 Years - 79 Years	45	55	100	14.0	15.5	14.8
80 Years - 84 Years	93	105	198	44.3	40.5	42.2
85 Years - 89 Years	111	161	272	89.1	88.3	88.6
90 Years - 94 Years	97	215	312	195.4	225.5	215.2
95 Years - 115 Years or more	53	123	176	454.7	409.9	422.4
Total	511	744	1,255	4.2	6.0	5.1

Footnote(s):
(a) Causes of death data for 2017 are preliminary and subject to a revisions process. See Explanatory Notes 57-60.
(b) Age-specific death rates. Deaths per 100,000 of estimated resident population as at 30 June (mid year). See Glossary for further information.



Influenza deaths by state and territory of usual residence

All states and territories except Western Australia experienced an increase in the number of deaths due to influenza in 2017. New South Wales recorded the largest numerical increase with 311 more deaths due to influenza than in 2016. Although recording only a small amount of deaths, Tasmania reported the largest percentage increase from 2017 (370%) and the highest rate of death within all states and territories at 5.7 deaths per 100,000 capita. The three most populace states, New South Wales, Victoria and Queensland, recorded 82.5% of deaths due to influenza in 2017.

Number and standardised death rate of Influenza deaths (J09-J11), by state - 2016 and 2017 (a)(b)(c)(d)

Influenza deaths (J09-J11)	No. of Influenza deaths 2016	No. of Influenza deaths 2017	Rate of Influenza deaths 2016	Rate of Influenza deaths 2017	% Change (no.)
New South Wales	183	494	1.7	4.5	169.9
Victoria	68	277	0.8	3.3	307.4
Queensland	107	264	1.9	4.4	146.7
South Australia	48	128	1.8	4.6	166.7
Western Australia	34	22	1.2	0.8	-35.3
Tasmania	10	47	np	5.7	370.0
Northern Territory	np	6	np	np	np
Australian Capital Territory	12	17	np	np	41.7
Australia	464	1,255	1.5	3.9	170.5

Footnote(s):
(a) np - not available for publication but included in totals where applicable, unless otherwise indicated.
(b) Causes of death data for 2017 are preliminary and subject to a revisions process. See Explanatory Notes 57-60.
(c) See Explanatory Notes 75-106 for further information on specific issues related to interpreting time-series and 2017 data
(d) Standardised death rates for 2013-2016 presented in this table have been calculated using final re-based estimated resident population based on the 2016 Census. As a result, these rates may differ from those previously published. Age-standardised death rates for 2017 presented in this table have been calculated using preliminary estimated resident population based on the 2016 Census.

Common associated causes

Persons with existing health problems, weakened immune systems and older adults are at higher risk of influenza. In 2017, persons who died from influenza had an average of 4.3 conditions listed on their death certificate, compared with 3.4 for overall deaths.

The graph below presents the most common conditions certified as being a contributory factor to death for those who died of influenza in 2017. Dementia including Alzheimer's disease and chronic obstructive respiratory diseases were the most common certified conditions, present in approximately 25% and 20% of deaths of people who died from influenza respectively. Cancer, a disease known to severely weaken the immune system, was present in almost 10% of fatal influenza cases.



Influenza incidence and mortality 2017

The National Influenza Surveillance Committee reported that the 2017 influenza season recorded the highest levels of influenza activity since the 2009 swine flu pandemic (NISS, 2017). In addition, the season started approximately one month earlier and the peak period of influenza was prolonged. The table below shows mortality due to influenza in 2016 and 2017 and the number of confirmed laboratory notifications through states and territory health authorities over the same period. There is a strong correlation between the increase in confirmed influenza cases and the increase in mortality due to influenza, with confirmed cases being 2.8 times higher in 2017 than 2016, and mortality being 2.7 times higher over the same period. This pattern is consistent across all states and territories.

Influenza deaths and laboratory confirmed notifications, number and ratios - 2016 and 2017 (a)(b)(c)(d)

Influenza (J09-J11)	No. Influenza deaths in 2016	No. Influenza deaths in 2017	No. Laboratory confirmed Influenza notifications in 2016	No. Laboratory confirmed Influenza notifications in 2017	Mortality Ratio Increase	Notification Ratio Increase
New South Wales	183	494	35,577	103,857	2.7	2.9
Victoria	68	277	12,924	48,120	4.1	3.7
Queensland	107	264	23,284	56,584	2.5	2.4
South Australia	48	128	7,866	28,498	2.7	3.6
Western Australia	34	22	7,830	6,005	0.6	0.8
Tasmania	10	47	1,055	3,506	4.7	3.3
Northern Territory	np	6	701	1,474	np	2.1
Australian Capital Territory	12	17	1,603	3,098	1.4	1.9
Australia	464	1,255	90,840	251,142	2.7	2.8

Footnote(s):
(a) np not available for publication but included in totals where applicable, unless otherwise indicated.
(b) All causes of death data from 2006 onward are subject to a revisions process - once data for a reference year are 'final', they are no longer revised. Affected data in this table are: 2013 and 2014 (final), 2015 (revised), 2016 and 2017 (preliminary). See Explanatory Notes 57-60 in Causes of Death, Australia, 2017 (cat. no. 3303.0). and Causes of Death Revisions, 2014 Final Data (Technical Note) and 2015 Revised Data (Technical Note) in Causes of Death, Australia, 2016 (cat. no. 3303.0).
(c) See Explanatory Notes 75-106 for further information on specific issues related to interpreting time-series and 2017 data
(d) Laboratory confirmed Influenza notifications accurate at time of publication (Source: http://www9.health.gov.au/cda/source/cda-index.cfm)

In temperate climates such as Australia, influenza is generally active during the winter months, with surveillance systems typically operating between May and October. The figure below shows the number of deaths due to influenza by month in 2017 and 2016. Although the proportion of deaths is highest in both August and September across both years, accounting for 58.4% and 72% of all fatalities from influenza respectively, the prolonged peak in deaths across July to October in 2017 is evident. This aligns with confirmed laboratory influenza case peaks across the 2017 August and September period.



References

1. Department of Health 2015, What is influenza? Viewed September 7th 2018. http://www.health.gov.au/internet/main/publishing.nsf/Content/about-pandemic-whatis

2. National Influenza Surveillance Scheme (NISS), Department of Health 2017, Australian Influenza Surveillance Report - 2017 Season Summary. Viewed September 10th 2018. http://www.health.gov.au/internet/main/publishing.nsf/Content/097F15A91C05FBE7CA2581E20017F09E/$File/2017-season-summary-22112017.pdf