Flu may not be peaking even if it looks like it is right now…and here’s why

Influenza laboratory confirmed Flu test data from the US Centers for Disease Control and Prevention.

The United State’s (US) influenza (Flu) season looks like it has peaked according to the latest Flu report.[1] And perhaps it has. But the graphs are only as solid as the numbers that go into them. And they are a bit wobbly for a little while. This is not a criticism and it’s not a bad thing, it just is what this is.

Each week, hard-working epidemiologists and report-makers collect, collate, confirm, curate and present the numbers that provide the public – and other professionals – an idea of what is happening in their neck of the woods.

But as with all things outbreak and epidemic, we have to have the patience to see in what way the case numbers are turning. The fog of Flu virus spread is as strong as that of MERS-CoV, Ebola virus, Zika virus or any fast-paced disease transmission event. My best guess at how much time that takes is about 3 weeks.

I used an online tool called WebPlotDigitizer [2] to get an estimate of the totals shown in the CDC Flu test-positive bar graphs. I worked that out for Week 52|2017 through to Week 5|2018 and then rounded them in various ways using Microsoft Excel.

Snapshot of the interpolated Excel data I collected & used to estimate the time it takes for US CDC weekly Flu data to settle down.

That showed me that if you look at a given Week’s total, it will take about 3 more weeks before that Week’s total stops rising. These rises are presumably from newly added lab data that have missed the weekly deadline and have arrived after a weekly report’s publication deadline. This same pattern can be seen in the United Kingdom’s Flu reports and Australia’s Flu reports; probably anywhere you look.

Once again, this isn’t a problem. It’s a good thing because it means when we look back we’ll have the best data we could. These should be living documents – at least until the last tissue has been binned.

When it does become a problem is if one uses the current graph’s pattern to make an absolute statement about where the Flu season is right now. That doesn’t work. Keep the comments flexible. 

And have patience.


  1. Weekly U.S. Influenza Surveillance Report
  2. WebPlotDigitizer

Views: 13708

7 thoughts on “Flu may not be peaking even if it looks like it is right now…and here’s why”

  1. Thanks for doing this! I was thinking of doing the same after noticing the huge jump in week 4 numbers in the week 5 report, but didn’t have the time to pull the data together. Looking at the differences between weekly reports over time, it looks like we are getting close to a peak – at least I don’t expect a huge jump relative to week 4…

  2. Ian, I would be interested in seeing a post

    1. Regarding the influence on media attention and laboratory testing. We are seeing many hospitals here testing patients if they will be admitted to the hospital. Meaning, it is a risk management strategy but one that is likely influencing the statistics reported for outpatient and hospitalization rates.


    2. The issue with NSW / Aus changing their mortality reporting protocols mid-season, which resulted in an apparent elevation in mortality. This was later reported in NEJM and raised quite a number of concerns about validity.

  3. What is the difference between the flu and flu-like illness? The flu is “a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs,” the CDC says. It says symptoms include some or all of the following: Fever Cough and sore throat Runny or stuffy nose Muscle or body aches and chills Headaches Fatigue “Influenza-like illness,” also called “flu-like illness,” is a more wide-ranging category. The CDC says that with flu-like illness, you have a fever of at least 100 F and a cough or sore throat, but the cause of the symptoms isn’t known. How can doctors tell if you have flu or flu-like illness? The flu is diagnosed from a swab test of your nose or throat.

  4. Ian, we (re)activated the health security intelligence blog (http://healthsecurityintelligence.typepad.com). The bottom line is this: media hype indeed does drive patients to go see their healthcare provider. Media hype also dramatically influences lab testing- every hospital we’ve interviewed indicated they test everyone in triage or prior to admission to the hospital. This of course will move your numbers up. The biggest clue this was happening was the mortality stats are simply not that unusual, as was noted in Australia. Also noted in Australia was the expanded availability of rapid testing in the clinical setting. The bottom line is the collision of Australia’s initial misinterpretation of the data, media hype (driven by threats to CDC’s budget from the Administration), decreased per capita bed capacity in US hospitals, and ongoing anti-vaccination sentiment has played a role in over-reporting. In my world, this is referred to as, “an intelligence failure” and one that Australia should examine as well.

  5. Not relevant to this post, but thought I should answer a scifi question. Firefly is owned by Fox. Whedon and years later patrick rothfuss tried to buy the rights to an exceptional series. To no avail. Remarkably prescient and timely considering…

Comments are closed.