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Comment by ineedasername | Hacker News Reader

There is literally an entire industrial complex setup to fight the flu on an annual basis, including massive testing & tracking. This is how we have data on annual flu infections. If anything, this year would have been an excellent year to find more flu infections as many people who got sick didn't simply stay home and get over the illness, they went & got tested.

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I've never known a doctor actually run a test for flu. You couldn't even get a test for Covid either for much of last year, even if the symptoms were blatant. I know a few people who simply stayed home with Covid symptoms and never ventured out to a doctor - and thus were never counted in the statistics.

I had bad flu last year and because of home working, I went back to "work" once I reached the number of days after which I needed a doctor's note. In normal times I'd have gone to the doctor to get a sick note rather than infect my colleagues.

Your awareness on flu testing is an indication of the limits of your knowledge, not a lack of testing. Others in this discussion have provided links with hard data on testing from the CDC for the US. For a world-wide picture, FluNet w/ GISRS also provide data on testing.

These form the basis of overall infection estimates. If you are interested in the methodology of those estimates, here is the CDC overviews, complete with citations for the primary research that informed the creation of their models: https://www.cdc.gov/flu/about/burden/how-cdc-estimates.htm#e...

do people coming in to get tested for corona generally get tested for the flu?

Not in the UK. My cousin just had a bad dose of something. It's not covid (negative test, he's vaccinated and he had covid a few months ago) and it's not life-threatening so, quite reasonably, nobody cares what it is.

Early in the pandemic, absolutely. It was easier/quicker to test for the flu and rule out covid, than test for covid to rule out the flu.

How does testing positive for the flu rule out covid? What is to prevent someone from having both?

No idea on the technical answer, but the healthcare logistics answer is that because it's not all that likely, a positive flu test was a decent stand-in when COVID tests weren't widely available.

Say 1 in 10 people have flu and 1 in 10 have covid. In a population of 100, 9 have just flu, 9 have just covid, and 1 has both. Those 19 people present similar symptoms, and anyone among them has roughly a 53% chance of having each disease. They take a flu test and it comes up positive. Now they're either one of the 9 with just flu, or the one unlucky person with both, so there's only a 10% chance they have covid.

The impact of this effect changes if has-flu and has-covid are correlated, but it's still there unless it's a 100% correlation.

The technical term is "explaining away". If a burglar alarm goes off, you can be pretty sure someone triggered it. If there also was an earthquake at the same moment, you can be pretty sure of the opposite. Even though both events can happen at the same time.

Don't know how widespread it was, but for my wife who had bi-weekly Covid tests for work they also started testing the samples simultaneously for the flu.

I went to the hospital a few months ago for something that could have been covid-19 and they did test the various influenza strains as well as the covid one. Not sure how representative that is though. I don't think the covid-19 swab or gurgle tests automatically test for the flu as well.

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