SunFluwer…

Just for fun, I thought I’d check in on Australia’s influenza tally again.

I posted my last tally 3 days ago (Jan 18) and upon looking today (Jan 21), it’s risen by 592 confirmed cases.

What it means, I do not know, but there is certainly a lot of laboratory testing going on out there in this sunburned land.

We can see from the graph below, one obvious fact that we need to be clear on: there are more cases than normal for this time of year, but we’ve just come of a very low peak season (winter). So the discussion that follows is talking about bigger-than-usual-for-this-time-of-year not “arrgh, flumageddon levels of bigness!” Yeah” (please the comments section for more chattery)

Having said that, the peak 2018 flu season month of September had fewer than twice as many notifications across Australia as we saw in the very hot summer month of December.


Australia-wide confirmed influenza cases using data from the National Notifiable Disease Surveillance System, (NNDSS)[1]

This time I’ve drilled a little further into our national flu numbers (which don’t have any virology attached to them) and made some new graphs.

2019 Flu cases by place, age and sex

We can see in the graphs below (zoomed in to see January 2019 on the right; click to enlarge) that most flu cases traditionally occur in the two states of New South Wales and Queensland on the east coast of Australia, each year.[2] That pattern seems to have shifted a little in January 2019, with Queensland leading the tally over NSW. A little different but with plenty of precedent from previous years.

That pattern seems to have shifted a little in January 2019, with Queensland leading the tally over NSW. A little different but with plenty of precedent from previous years.

In the next graph, we see the age and sex breakdown for 2019 so far (21 days).[3] While only based on 3,273 cases, we can see the usual big impact of flu among the very young, but also a similarly high bump across the middle age groups (from 15-19 through to 60-64) dropping away after that.

Australia-wide confirmed influenza cases using data from the National Notifiable Disease Surveillance System, (NNDSS)[3]

For comparison, I’ve graphed the sex and age group data [3] from a few recent years as well. This probably is a poor comparison because in 2019 we’re only looking at a “pattern” made up from just one, non-peak flu month whereas the graphs below comprise whole years worth of cases. I don’t have access to age and sex data from January for the other years, so we have this. Remember to watch for the patterns and note that the total numbers which differ from year to year (see the y-axis; click on the images to expand).

I have no idea if the January 2019 bump in the teenage to 65 year age groups of Australia’s influenza tally is meaningful or even if it differs from January in other years or not. But, it is interesting to see. I’ll keep watching this as the year goes on.

The old testing debate

One last thing; the role of testing in our big summer.

People go to a doctor or hospital and get tested for flu if they have a flu-like illness. In 2018, the Australian peak flu season was the lowest we’d seen it in the 4 previous years. Because of that, it might look like the off-season is comparatively large. It isn’t. As I said earlier, it’s just larger than normal.

It’s worth stating that increased testing ability doesn’t just default to meaning “now everything will be higher because testing”.

What more testing means is that we’re probably going to keep seeing a raised baseline out-of-season compared to what we used to see a few years ago.

We’ve seen rising numbers with the change from culture to PCR, from conventional PCR to real-time PCR; whenever testing methods get better. This time they have got faster and this has driven their uptake. Just how much of a bounce to the baseline is still unclear and could do with being described. More than twice as high – which is rise we saw at the end of 2018? Mebbe.

Where is the testing activity hottest?

We know that 64% of January’s 2019 Australia’s influenza tally came from two states; New South Wales and Queensland (1st and 3rd most populated in Australia; combined they comprise 52% of the population.[6]).

We also know these two states have eagerly embraced rapid result molecular testing in hospitals, on top of existing laboratory testing.[4,5]

So perhaps this summer 2019 is all about testing and creating the new normal. Or perhaps it’s not.

References

  1. Number of notifications of Influenza (laboratory confirmed), Australia, in the period of 1991 to 2018 and year-to-date notifications
    http://www9.health.gov.au/cda/source/rpt_3.cfm
  2. Number of notifications of Influenza (laboratory confirmed), received from State and Territory health authorities in the period of 1991 to 2018 and year-to-date notifications for 2019
    http://www9.health.gov.au/cda/source/rpt_4.cfm
  3. Number of notifications of Influenza (laboratory confirmed), Australia, 2019 by age group and sex
    http://www9.health.gov.au/cda/source/rpt_5.cfm
  4. https://thenewdaily.com.au/life/wellbeing/2017/08/18/flu-season-virus/
  5. https://www.news.com.au/national/queensland/flu-shot-2018-health-minister-steven-miles-urges-queenslanders-to-get-flu-jab/news-story/7cd805cf8027f2e698228b671f299e0c
  6. 3101.0 – Australian Demographic Statistics, Jun 2018
    http://www.abs.gov.au/ausstats/abs@.nsf/Latestproducts/3101.0Main%20Features1Jun%202018?opendocument&tabname=Summary&prodno=3101.0&issue=Jun%202018&num=&view=

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