The 2019 Flunami was more than just increased testing

Posted onAuthorIan M Mackay, PhD (EIC)

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 vaccines. Becuase flu seasons are complex.

Image from Intense interseasonal influenza outbreaks, Australia,
2018/19, Barr et all, August 2019, Eurosurveillance

Australia’s national definition of the severity of our flu season focusses on the number of deaths and/or the number of intensive care unit (ICU) admissions among confimred 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 hospital with flu is also up in 2019. In fact, it’s at the second-highest total in the past 6 years according to data from a collection of “sentinel” hospitals reporting data from across Australia via the FluCAN network.

Data are a close approximation of the actual values. Data were harvested from Figure 3 of the Australian Influenza Surveillance Report No.7, 2019, using WebPlotDigitizer. While not a severe flu year, the flunami of 2019 has put an extra burden on hospitals because people are actually sick.

Residential care facility flu outbreaks

Another measure that supports the signal testing data has been sending us in Australia since summer, is the number of flu outbreaks in residential care facilities.

Data from Influenza Weekly Report, NSW Government and Victorian Weekly Influenza Report, Victoria State Government.

The state of Victoria seems to have only recently begun to report such outbreaks so there may still be issues around communications between facilities and public health and getting testing done etc. Nonetheless, based on what numbers we have in hand, there have been more outbreaks in 2019 than in the other two years recorded. 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 New South Wales Government Department of Health, testing for influenza-like illness in that jurisdiction rise 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 deifintely about more than just increased testing.

But have a look at the graph of the proportion of those samples that test positive for flu (blue line in the graph below). It’s all over the place by comparison. That’s because flu seasons are complex. Sorry, But they are. There’s no simple answer that can be reached by guessing. They reply on the population’s immunity, age, the nature of the flu viruses in the local ecosystem and those which seed that ecosystem from overseas as well as the vaccine and the weather.

Data from Influenza Weekly Report, NSW Government. Data are a close approximation of the actual values. Data were harvested using WebPlotDigitizer.

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 back these suspicions up.

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

It’s clear that flu-positive test numbers were up in 2019 but it was about more thn just increased testing. Medically diagnosed illnesses due to flu infection were up in 2019. Just because the season has been classified as of “low severity” by one definition, don’t let that downplay the significant impact to hospitals, workplaces, schools, families and the elderly.

Next year, consider that flu vaccine if your Doctor agrees 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.

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