Is increased testing at the root of Australia’s biggest ever first quarter of Flu cases…?

I’ve seen some media reporting an “early start to the flu season”. Is this true?

The short answer is – I don’t know. Let’s explore why I can’t answer my own question.

Hot flu cases (‘notifications’) in Australia over 26 years.

January, February and March of 2018 recorded the highest number of laboratory- or kit- confirmed flu notifications of any previous year on Australia’s national record of such things.[1] You can see this in the table below – they are the hottest (most red) of the values for these months in any year between 1992 to 2018.

Granted, the early years didn’t capture many flu cases probably because there wasn’t much testing done; testing was insensitive and reporting may have been less systematic or organised.

Number of Influenza notifications by month and year from the National Notifiable Diseases Surveillance System, Australian Government, Department of Health. http://www9.health.gov.au/cda/source/rpt_3.cfm. I used Microsoft Excel to grade the columns (months from 1992 to 2018) by colour; green is fewest through to red representing most notifications for that month.

Broadly speaking, each month in recent years has seen more notifications than the same month in the year before.

Other factors that also increase over time is population size and testing (more later).

Hot starts, peaky peaks and some patterns to flu in Australia.

If you use this heat gradient approach to look at annual notifications in that same table you can see a couple of other patterns:

  • peak flu season in Australia pretty consistently occurs in July to September but rises and falls for a couple of months either side of that 
  • the start of each year never has more cases than the flu season (which is why it’s called a peak period) so we can safely expect to see more cases during the months of peak flu.
  • there are sometimes smaller peaks and troughs in notification numbers and flatter or sharper peaks (see the graph down below) but broadly speaking we see our total annual notifications grow over time  
  • 2017 was a stand-out year for flu (A/H3N2) in Australia – over twice the total number of notifications of any previous year. More testing may have played a role, plus a vaccine mismatch, plus lots of flu strains co-circulating, plus suitably susceptible populations, plus low vaccine uptake in some groups

The number of Influenza notifications by month and year from the National Notifiable Diseases Surveillance System, Australian Government, Department of Health. http://www9.health.gov.au/cda/source/rpt_3.cfm. I again used Microsoft Excel to grade the rows (each year from Jan to Dec) this time by colour; green is fewest through to red representing most notifications for that year.

What does it mean??

There must be a huge flu season coming!! Flumaggedon!! Arrggh!!!!……rrrgh!!…..gggh..!!

Amiriiiite????

Well, probably not. Also, I’ve got no evidence to support that so why say it?

These high numbers could be because of more widespread flu transmission or more people getting sick due to the nature of the viruses circulating…for some reason.

But higher reported case numbers could also be due to a few other things:

  • media fascination with Flu driving more flu virus testing. How? More of the public may go to their Doctor, perhaps even more frequently push them for flu virus testing to satisfy a need to justify multiple sick days off work.
  • doctors become more aware of testing and the need for it; confirmed influenza infection with illness is a notifiable disease after all.[7]
  • tests have also become much better – much faster and much more sensitive than those we used to diagnose infection by growing infectious influenza virus from a patient sample using cell culture methods. Did I mention today’s diagnostic tests are much better? 
  • relatively new, highly sensitive (PCR-based [10,11]) “point-of-care” (POC) commercial flu-testing machines have also been rolled out to hospital emergency departments, especially on Australia’s east coats, allowing more and faster testing and reporting of results.[2-6]
    • in the Australian State of New South Wales, these seem to be the Cepheid GeneXpert platform.[5,8-9]
    • I’ve not found any public detail about what diagnostic platform is being used in Queensland.[6]

Why is 2018 looking so big so early?

I still don’t know.

Without specific detail or data I’d guess that a big chunk of the high number of 2018 out-of-season flu positives is due to greater enthusiasm for testing, improved capacity (those new POC machines) to test and generally ever-improving access to, and awareness of, testing. 

I hope that at some point those who have access to the relevant data can report on whether the proportion of flu positives (the number of positive samples divided by the total number of samples tested) is growing and is higher than normal, or lower…or about the same. Having this denominator is really helpful. Some might say, essential. And yet it is often missing.

Lastly, having good comprehensive virus data available can help the mainstream media to get the right story out which in turn can reduce the number of “flumaggeddon” stories which in turn can have many flow-on effects.

Get your vaccine. Talk to your Doctor about when to get vaccinated, or keep an eye on your social pipes for the usual national health campaigns advertising the best time to get vaccinated (later in April onwards).

References…

  1. National Notifiable Diseases Surveillance System.
    Select “Influenza” from the notifiable disease list
    http://www9.health.gov.au/cda/source/rpt_3.cfm
  2. https://www.sbs.com.au/news/free-flu-vaccine-for-qld-kids-under-five
  3. https://mysunshinecoast.com.au/news/news-display/hi-tech-detection-and-protection-in-place-this-flu-season,53977
  4. http://www.abc.net.au/news/health/2017-09-28/flu-epidemic-your-questions-answered/8992884
  5. https://thenewdaily.com.au/life/wellbeing/2017/08/18/flu-season-virus/
  6. http://statements.qld.gov.au/Statement/2017/10/18/faster-detection-key-to-improving-flu-response
  7. Australian national notifiable diseases and case definitions
    http://www.health.gov.au/casedefinitions
  8. http://www.cepheid.com/en/cepheid-solutions/clinical-ivd-tests/critical-infectious-diseases/xpert-flu
  9. http://www.cepheid.com/en/cepheid-solutions/clinical-ivd-tests/critical-infectious-diseases/xpert-xpress-flu-rsv
  10. https://virologydownunder.blogspot.com.au/2015/05/the-mechanics-of-polymerase-chain.html
  11. https://virologydownunder.blogspot.com.au/2015/05/what-is-pcr-and-what-does-positive.html

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