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Comment by stuartbman | Hacker News Reader

So some big limitations, speaking as a doctor. Firstly, I'm surprised that they allowed watches on the ward. They're a huge infection risk and most places are bare below the elbows (NHS), moreso for covid. Secondly, they only looked at symptomatic covid cases (1 day before symptoms started was their prediction as far as i can tell. This is completely useless as the 24hrs before symptoms start the patient is likely to already be highly infectious, and misses the asymptomatic carriers which have an indeterminate effect on spread as well. Far better to use the semi-proven (but equally controversial) lateral flow tests and avoid these risks. In the UK, hundreds of healthcare staff have been identified as covid+ >48hrs before symptoms in this way.

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Speaking as a non-doctor, I don't have any lateral flow test supplies or equipment. Do they sell that on Amazon?

But seriously, a test I don't have easy access to is not an alternative. A lateral flow test has no predictive value to me because I'm never going to get one before I'm actually sick.

> But seriously, a test I don't have easy access to is not an alternative.

Do you have access to the custom Apple Watch app they used here? I don't either.

Health authorities could make either of these available to the general public -- the parent poster is making a comment about which is more valuable under the assumption of access.

You're not wrong, a test you don't have access to obviously has no predictive value for you, but right now we (the public) have access to neither, so this isn't a distinguishing factor.

Now, if you're making the argument that the Apple Watch app would be easier to distribute, then you can read the parent's criticism as "sure, but only knowing after you've potentially spread it is not very useful."

> Do you have access to the custom Apple Watch app they used here? I don't either.

That's pretty immaterial when discussing theoretical effectiveness. Obviously, getting wide use depends upon it getting packaged up into an app listed on the app store, and some sort of awareness push.

That needs to be done once, by the app's authors. For lateral flow tests, to have similar effectiveness, that means that literally every Apple watch wearer (just to assume a similar population size) needs to get themselves a supply of tests (and keep getting new tests when they run out), and remember to perform the test every day. That is a much higher hurdle to jump than getting this app onto people's watches (assuming their study is correct and can be independently verified!). I also expect the supply of test kits is not robust enough to handle that kind of demand.

> Now, if you're making the argument that the Apple Watch app would be easier to distribute, then you can read the parent's criticism as "sure, but only knowing after you've potentially spread it is not very useful."

Reducing spread potential by 24 hours when you've perhaps been spreading it for a week already isn't exactly a game changer, but it's still useful, especially if the only thing people have to do is install an app on their watch. Expecting everyone to obtain rapid test kits and test themselves daily is in general a non-starter.

> That needs to be done once, by the app's authors.

Except...it also needs FDA approval as a diagnostic, etc., which is probably easier said than done.

Obviously it's easier to distribute an app than lateral flow tests -- but the latter are much more effective too.

Clearly, we should do both, and...

> Reducing spread potential by 24 hours when you've perhaps been spreading it for a week already isn't exactly a game changer, but it's still useful, especially if the only thing people have to do is install an app on their watch. Expecting everyone to obtain rapid test kits and test themselves daily is in general a non-starter.

This totally depends on your goals. For the individual with limited outside exposure, is knowing 24h before you feel symptoms useful? Absolutely.

For a hospital or other institution (school?), who can order in bulk, and then mandate, lateral flow tests every day before work starts and observe their correct use (without having to rely on self-reported app results), the tests seem much more useful.

The data is all readily available in the default Apple health app.

Yes, to make these same predictions you'd have to do some statistics as described in the paper, but no special app is required.

(And that's why this finding is interesting: they have the data available from patients before they were sick, because every new Apple Watch records this data out of the box.)

Yes, the finding is definitely interesting because it suggests that we could make this available very broadly (i.e., anyone with an appropriate Apple Watch) without needing to ship a bunch of hardware.

But the limitations are worth noting: you may already have infected people by the time this detects your illness. That isn't true for lateral flow tests, making the latter more useful as a preventative testing tool (again, in the absence of access differences).

However, I don't understand what you're trying to say with this claim:

> Yes, to make these same predictions you'd have to do some statistics as described in the paper, but no special app is required.

"Do some statistics" is approximately as impossible as "order lateral flow test reagents" to the general public -- a consumable version of either the process described in this paper, or the lateral flow kits mentioned earlier, needs to be produced by someone skilled here, in order for this to be useful to the general public.

Can’t it still be useful by allowing contact tracers to get started earlier?

Lateral flow tests are rapid test kits to my understanding, so they should be available on Amazon if accepted by your local medical devices authority.

On the other hand Apple Watch costs like 400$ and UK just bought 400M lateral flow tests for 1.3Bn pounds

https://www.bmj.com/content/372/bmj.n287

Or you can buy it online for 250$/10 tests (if you can swallow that you're being fleeced this much)

Getting a warning 24 hours "early" that you might be infected is still useful. Perhaps in that 24 hours you were going to make a grocery trip and potentially infect a bunch of people, but now you won't because you got that early warning.

Claiming that something is useless because it doesn't cover all cases seems a little weird to me. It's a tool in the toolbox that can reduce the possibility of spread in a limited set of cases.

Using lateral flow tests requires everyone to purchase a big supply of them and use one every day. This watch-based warning just requires you to have an Apple watch and run a new app on it (which I hope they'll make publicly available), and it'll just let you know without any extra action taken. Your average Apple watch user is probably pretty likely to take the simple step of installing a new app; they're not going to buy a supply of lateral flow tests (which they probably don't even know much about or haven't even heard of) and test themselves every day.

Yup. I was lucky the person whom I contracted COVID from informed me the moment they got the test result. I was on my way to work, just about to leave the car. Turned around and went back home. Developed symptoms the same evening. It was a lucky coincidence that was Monday so I've stayed home the whole weekend and had no contacts for a couple of days I was likely already infectious. (The person I got it from only developed symptoms two days after our contact). People who do contact tracking only on Wednesday. So my contact informing me saved three days worth of my potential contacts from getting COVID from me.

Hope you're fine now. Can I ask how did you contract it? What I mean is: did you and the other person follow the usual distancing rules (mask + 1 meter apart + no touching)?

Only if you're willing to share of course :)

I can only comment on the study in front of me, and not the use cases that 'might have been'. In this case, they tested in a healthcare setting as there is a presumed higher risk of catching covid amongst participants. Would the same false positive rate be true in the community, where transmission is much lower? We don't know because that wasn't the experiment. The study authors claim that this is useful in the healthcare setting- I'm saying that it's useless because there are better tools in the arsenal (lateral flow tests), and watches are an infection risk.

You state:

> they only looked at symptomatic covid cases

Which means the study cannot be used to prove or disprove this claim:

> and misses the asymptomatic carriers

Why is there such a need to hastily dismiss any potential improvement?

Did they perform regular PCR testing on staff? No, and so they didn't detect any asymptomatic carriers. By comparison, all NHS staff are doing biweekly lateral flow tests, and hundreds of staff are detected prior to symptoms this way. This means that fewer staff are off sick/isolating, and more staff are available to care for patients.

It’s a study. A completely harmless, simple study that does not preclude anything else and shows positive results. What is your complaint? That it isn’t 100% definitive in all cases? That something else is better? That’s not the way progress is made.

Something that detects 10% of cases and is completely free (using a device people are wearing anyway) is valuable. You can be sure that some of these cases would have been missed by all the other tests, simply because not every one of these cases got any test at all.

> This is completely useless as the 24hrs before symptoms start the patient is likely to already be highly infectious, and misses the asymptomatic carriers which have an indeterminate effect on spread as well.

Nothing is a one-shot-solve-all solution to Covid. If Apple watches can detect it and prompt people to go get a full test, that’s great. I’ve got an ongoing theory that a lot of the spread is by people who ignore their symptoms because ‘they have a cough but it’s not a covid cough’ or ‘they haven’t lost their smell so it can’t be covid’ so the more things that can prompt you to get a test and isolate the better.

A "bare below the elbows" policy makes sense and there indeed are studies corroborating that pathogens can accumulate on wristwatches.

However, having worked as a paramedic I'm wondering how you would actually measure a patient's heart rate without a watch and with no additional equipment around.

Not every patient will be on cardiac monitoring, after all.

Yes, there are those nurse watches you can attach to your shirt or white coat but in order to take a proper look at those they have to be touched as well, which kind of defeats the purpose.

Why are watches an infection risk?

I assume it's because they accumulate crud and bacteria. You can wash your hands but you never really wash your watch. I also assume that because it's on your wrist every time you scratch your body or touch your face the bacteria covered watch deposits something icky on contact.

For reducing infection risk one option is to keep the watch in a pocket while working on the ward and wear a separate wireless heart rate monitor on the chest or upper arm. I don't think they did that in this study, just pointing it out as an option for healthcare workers who want to track their HRV on the job.

it is not unheard of for something at level x to be developed to level 2x so if it can do 24h now, with higher sample rate and better maths, what if it got to 48h in tractable time?

to the watch-in-a-ward point: valid. But, if this technique did get to 48h+ predictive quality, and was available to wearers of smart watches outside of wards would you still have hesitancy to consider it useful?

The utility of the test decreases with reduced risk. A 99% specific test is good when there are high levels of disease going around (e.g. covid in a hospital). In the community, rates are much lower, so the positive predictive value of the test is much lower, even with 99% specificity. My conclusion is that if you tried this in a community setting, the number of false positives would far outweigh the true positives, and lead to dismissal of alerts.

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