The Flunami (see a definition here before you decide upon your own dear reader) has been a rising tide of influenza cases. It was more than just increased testing, though. It was about sick people. And travel. And virology. And immunity. And an early start. And a prolonged season. And vaccines. Because flu seasons are complex.

Australia’s national definition of the severity of our flu season focuses on the number of deaths and/or the number of intensive care unit (ICU) admissions among confirmed flu cases. That’s fine. But other indicators can also suggest how much of an impact a flu season is having.

Hospital admissions

The number of people admitted to the hospital with the flu is also up in 2019. In fact, it’s the second-highest total in the past 6 years, according to data from a collection of “sentinel” hospitals reporting across Australia via the FluCAN network.

Residential care facility flu outbreaks

Another measure that supports the signals from Australian testing data since the summer is the number of flu outbreaks in residential care facilities.

The state of Victoria seems to have only recently begun reporting such outbreaks, so there may still be issues with communication between facilities and public health and with getting testing done, etc. Nonetheless, based on the numbers we have on hand, there have been more outbreaks in 2019 than in the other two years. In New South Wales, the total is currently third highest over the past decade.

Testing is up, and people are sick

I may not have been clear in previous posts, but yes, testing is up. Using publicly available data from the New South Wales Government Department of Health, testing for influenza-like illness in that jurisdiction rose by an average of 1.3 times the total of the previous year, dropping in the milder 2018 season (red line in the graph below). But the 2019 flu season is definitely about more than just increased testing. Illnesses that drove test-seeking behaviours started earlier and lasted longer than in most previous years.

Not just totals, fractions also matter

But have a look at the blue line graph below of the proportion of samples that test positive for flu in one Australian jurisdiction. It’s all over the place compared to the fairly steady rise of the red line representing samples tested in that same location.

That’s because flu seasons are complex. Sorry, but they are. There’s no simple answer that can be reached by guessing. They rely on the population’s immunity, age, the nature of the local flu viruses this season and those that seed that ecosystem from overseas, as well as the vaccine, testing capacity, test ordering and the weather.

In some quarters during 2019, there seemed to be a reticence to accept that more cases of flu were occurring this year. As if testing was to blame for numbers rising, and that the media were driving people to seek care and get tested when they otherwise wouldn’t. There is bound to be some of that going on because everything about flu is complex. But 9X as much testing as any previous year (see May 2019)? Hopefully, those people are conducting studies to substantiate these suspicions.

And a paper released overnight explaining some of the virology (based around haemagglutinin sequencing and analysis) agrees.[1]

The 2018/19 interseasonal period (November to May) in Australia has been exceptional. Not only have notifications of laboratory-confirmed cases been high, but testing positivity rates, institutional outbreaks, deaths, and emergency department and general practice presentations
have all also been high.

Intense interseasonal influenza outbreaks, Australia, 2018/19, Eurosurveillance, AUG 2019

What’s up? Numbers, so overall harms are as well

It’s clear that flu-positive test numbers were up in 2019, but it was about more than just increased testing. Medically diagnosed illnesses due to flu infection were up in 2019.

Perhaps if we vaccinated more or had more effective vaccines, we’d be able to break the link between increases in total flu cases and increases in total harms. But we’re not there yet. For now, if we have more flu, we have more of every presentation – from mild to moderate to severe to fatal. What makes it a severe flu year is how many people who tested positive ended up in the hospital or died. 2019 has been summed up asboth a big season and a severe season.

Deaths were also higher in 2019 than in 2010 or 2014. ‘Influenza and pneumonia’ was the 9th leading causing of death in Australia in 2019 and also ranked 9th in 2017 although the number of deaths was a tad higher (4,124 on 2019 vs 4,269 in 2017) and the total number of cases was fewer.

Apart from death, there’s also significant impacts on hospital loads (overload emergency departments, increase ramping, delay scheduled procedures and drain resources), workplace and school absences and the ensuing disruptions, family stress and especially harms to the very young and the elderly. So a hot take take like “So far, the season is early but average. It’s not the worst flu season on record and not a “flunami”” only serves to further highlight that flu seasons are complex.

Next year, consider the flu vaccine if your vaccination source agrees that you and your family are among the majority who can happily receive it.

There is nothing else that can reduce the impact of flu. Well, nothing apart from y’all getting sick and then immune.

References…

1. Intense interseasonal influenza outbreaks, Australia, 2018/19
   https://www.eurosurveillance.org/content/figure/10.2807/1560-7917.ES.2019.24.33.1900421.

Updates

• 28FEB2026 – light editing to correct typos and grammar. Update comparison of 2019 to 2017 wiuht new links that summarised the outcomes of 2019.