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Comment by buscoquadnary | Hacker News Reader

So I had a sister that got sick, she took a test, not COVID. She was still sick a little while later, another test another negative. She finally took a third one and that returned a COVID positive test.

In the meantime my children have been sick for a little while, and we got one of them tested and it was negative; however right before they got sick we had interaction with someone who had a positive COVID test shortly thereafter.

I am starting to wonder at the efficacy of the tests and is it that they just can't catch Omnicron as well? Are my kids really just sick with some other random thing despite dozens of people in our social circle getting COVID?

I'm just wondering at this point if there is a reason for the mass testing, because it doesn't really let you know anything except whether or not you have COVID and you'll get better or get worse. I can understand in hospitals or something like that, but in the general population I am failing to understand as it seems Omicron is incredibly virulent, and you can spread before you have symptoms, so what is the end game with the mass testing?

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If you look at the actual testing data for antigen tests [0], the LoD for them is very high compared with PCR. This means a person needs a high viral load for tests to be effective. For example, the BinaxNOW kits require 140.6 TCID50/mL [1] vs 0.012 TCID50/mL for a PCR test (I picked a random one here) [2]. The FlowFlex tests are even worse, requiring 2500 TCID50/mL [3]. I personally purchased a few of the Lucira tests (not affiliated I promise) because they're more similar to an at-home PCR (they use LAMP) and so the LoD is lower (0.9 TCID50/mL) [4].

[0] https://www.fda.gov/medical-devices/coronavirus-disease-2019...

[1] (pdf) https://www.fda.gov/media/141570/download

[2] (pdf) https://www.fda.gov/media/142193/download

[3] (pdf) https://www.fda.gov/media/152698/download

[4] (pdf) https://www.fda.gov/media/147494/download

What unit of measurement is TCID50/ML? Just curious

https://iamanovice.wordpress.com/2011/03/31/tcid50/

I am admittedly not a virology expert but my understanding is TCID50 signifies the concentration at which 50% of the cells are infected when the sample is inoculated with a diluted solution of viral fluid.

Ripped straight from https://www.bio-rad.com/en-us/life-science-research/overlay/...

The amount of virus necessary to affect half (50%) of the cells in a sample.

Wow those package leaflets are impressive. We (in Germany) get those Chinese test on an emergency admission and all they have is a single table with specifity and sensitivity (no info on viral load at all). They are however cheap and they still work . The responsible agency is actually testing them recently and at least publish the results: https://www.eurosurveillance.org/content/10.2807/1560-7917.E... . Still they allow companies to sell obviously nonworking tests with nonreproducible test results.

Health officials in other countries have found it is much easier to detect omicron in the throat, and not the nose, with these antigen tests. This started with a big wave of people who were PCR positive but nose antigen negative. When swabbing the antigen in the throat, the false negative percentage dropped

Swab throat too during rapid COVID test, Israel's Health Ministry says

https://www.reuters.com/business/healthcare-pharmaceuticals/...

Thank you for that. It vibes with the people I know who likely caught Omicron, they all presented with sore throats.

Washington Post reported that there is some disagreement among experts: https://archive.fo/1bIa4

I would expect the FDA to push back against individuals doing throat swabs with an at-home test kit -- the organization approved these tests based on a specific testing protocol (nasal swab). The FDA won't offer alternative protocols until they've looked at test/trial data.

So wait, you're supposed to swab your throat and your nostrils now?

So what's better, getting your throat spit up your nose, or getting your nose mucus in your throat?

Follow the directions on the box. If it doesn’t say to swab your throat, maybe wait on that. Free styling on medical tests doesn’t always lead to repeatable results.

The article says throat first a couple times

The UK-issue lateral flow tests have always said to swab the throat (specifically the tonsils) and then both nostrils at about 2.5cm depth.

Every time you sniff, you get nose mucous in your throat (what with them being connected and all), and when you sneeze quite a bit of throat mucous will is drawn up along with air. And now remember that your intestines are physically connected to your mouth by only a foot or two of squishy pipe and you'll be wishing for a nice clean robot body.

Could get worse:

U.S. diplomats in China were subjected to anal swab tests for Covid-19, a Department of State spokesperson confirmed Thursday, adding that a protest had been lodged with the Chinese Ministry of Foreign Affairs.

https://www.nbcnews.com/news/world/u-s-diplomats-china-subje...

Antigen nose swabs are extremely unreliable, unfortunately. Barring public knowledge about this, the campaign could be ineffective at best or actively harm infection rate at worst.

Anecdotal: I was in my 3rd of 4th day of symptoms before I finally came up positive on antigen (at home and at testing sites; the test appeared to be the exact same). PCR showed it from day 0 but the results lag quite a bit especially right now in the US (it took 7-10 days for me to get the PCR back in early Jan).

Best I’ve heard it described is that Antigen tests are best for detecting high virulence on days 3-5 (e.g., when the spread is happening from tons of viral production, including in the nasal passages). They are more for public health usage to prevent spread rather than diagnostic like PCR.

That aligns with my experience, that if you test positive on antigen you are definitely contagious but if you test negative you may still have the virus present in your system. PCR amplifies it so it can detect even small viral load.

If only we had some guidance and solid communication from public health experts that you could conceivably trust..

> They are more for public health usage to prevent spread rather than diagnostic like PCR.

Like the grandparent, I know several people that have all of the covid symptoms, but tested negative early on. These people just go about their day because they think they have some other cold, then stop testing until their symptoms go away. I would probably do the same.

My thoughts exactly. I believe the widespread misunderstanding of how to use the different tests and interpret the results will end up hurting infection rates overall. For exactly the reason you mention - it lulls people into a false sense of security. I disagree with this person's take 100% especially since PCR testing has been all but abandoned in the face of the magnitude the omicron wave.

Until a PCR can be done within 15 min instead of 2-3 day turnaround, there will always be a gap in using PCR for public health purposes. That time may come in the future for faster PCR, but it is simply not the reality yet today and we have to rely on antigen tests to at the very least rely on detecting the most virulent days to prevent super spreader events.

In Wake County, NC, rapid high-sensitivity PCR tests are available at about a half-dozen sites with results in 12 hours. Appts are have been available within 24-48 hours depending on demand.

You drive into a parking lot, they hand you a test, you self-swab and give it back to them.

There is other testing available - this is just the county-provided testing. It’s well run.

If you search for PCR tests for travel, you can probably find same day tests.

The place I use in Austin is $85 for a same day PCR test.

They're not so much unreliable as ... really not very sensitive, as I understand it. Viral load in covid sufferers follows a curve with a rapid ramp up and a slower ramp down, both PCR and lateral-flow devices require a certain minimum level in order to read positive. PCR is much more sensitive (because it's an amplification technology, so can "see" a lower level of viral load) than lateral-flow devices - which means you can be "safe" on an LFD and "unsafe" on a PCR for a small amount of time on the ramp up and a fairly large amount of time on the ramp down. The level at which you're at risk of passing it to other humans is I _believe_ somewhere between the two tests, so it sounds like you maybe got unlucky with an LFD or two, but the results you report are about what I'd expect :(

LFDs are decent for telling you if you're infectious _right now_ - they're much worse than PCRs for telling you if you have covid at all.

Disclaimer: I'm a software engineer, do not take medical advice from me. My partner is a biochemist and I regularly chat with a couple of council covid-response officers, and the above is the explanation I've had from them when I've asked.

>I am starting to wonder at the efficacy of the tests and is it that they just can't catch Omnicron as well? Are my kids really just sick with some other random thing despite dozens of people in our social circle getting COVID?

Ever since the vaccines came out and were implemented in full force, I am wondering what the purpose of testing even is. At least in the US, even the most restrictive locales have no intention of shutting down commerce to limit transmission. I do not know anyone who is not treating this coronavirus like any other, or the flu, or a rhino, or whatever other sicknesses normally go around.

My kids' daycare (or local government, not sure which is responsible) has a crazy policy of shutting down a class for 2 weeks if a covid case is detected. But not if any of the kids are sick with RSV/flu/rhino/noro/rota, etc. The daycare has not had any reports of covid for months. I am pretty sure all the parents are simply choosing to not get their kids tested because who can afford to drop their obligations for 2 weeks and also force all the other parents in class to do the same. Every single kid walking through those doors has a snotty nose, and surely at least 1 has had covid 19 over the past few months.

The purpose is to know when to self-isolate and maybe give close contacts a heads up that they might be positive too.

Sure, but why is a test needed for that? Why not test for any of the other sicknesses then, and not just covid 19?

It all seems similar to security theater after 9/11. A lot of effort and expense for little gain so somebody can say they did something.

What if you don't have symptoms, but know you were exposed to Covid? What if your symptoms are mild and you aren't even sure are caused by a communicable disease?

If I isolated every time I got the sniffles or was more tired than usual I'd be home a lot..

Exactly, why is covid 19 still getting put on a pedestal? RSV is worse for kids than covid 19, yet daycare does not shutdown for 2 weeks because of RSV.

https://pubmed.ncbi.nlm.nih.gov/33015684/

Society's risk tolerances are being very inconsistent right now, and the only reason I can see is for political purposes (i.e. cover your ass).

Is it worse for adults / elderly? Are the long term risks of RSV as fuzzy as covid?

By the way, I'm not claiming we should be more strict about any of this, but on a personal level I'd rather do my best to not infect others.

I also want to do my best not to infect others, but I do not see people risking their economic livelihood to do that outside of those with the luxury of working from home.

I guess what I am getting at is the dichotomy of leaders officially acting if people should test and quarantine and all that jazz, while obviously knowing that those who need to go out and work to put food on the table and funds in the retirement account will continue to do so.

Based on the stats, I would bet all I have on one of those snot nosed kids at my kids' daycare having covid right now. But I am sure many or most of the parents need to work for the cash to meet the mortgage payments or whatever their expected quality of life is.

Even if somebody does have to go to work while sick with covid for whatever reason, they can avoid other nonessential contact with people based on their test result.

I do agree there's a lot of hypocrisy and ass-covering going on. Even earlier in the pandemic healthcare workers were discouraged from getting tested so they wouldn't need to stay home from work. I think making tests available prevents at least some unnecessary transmission which is good enough for me.

I think you are correct, making the tests available is probably good. Maybe we should have similar availability for other infections.

RSV isn't currently killing ~1800k Americans a day.

RSV has no vaccine unlike Covid 19. If people do not want to get vaccinated, then that is their problem.

https://ourworldindata.org/covid-deaths-by-vaccination

From that link, like 1 in 10 people dying are vaccinated. And even ignoring that, I will still personally choose to stay home when infected with covid even if it only helps the unvaccinated.

There's no approved vaccine yet for the daycare-aged population being discussed.

The daycare age population are not the ones dying. Point being that yes, COVID 19 is resulting in more deaths than RSV nationwide, but as a vaccinated individual, I am more concerned about RSV (one of my kids has already got it), than I am from COVID 19.

> The daycare age population are not the ones dying.

Which, if daycares were run by the toddlers independently of adult supervision, would be a great point.

Infected individuals often have a period where they are actively infecting others but not yet showing symptoms.

Right, same as all the other viruses floating around, that we also had before SARS-CoV-2 or covid-19 or whatever.

I get the initial lockdowns and period of time to figure out this new thing, but at this point in time, I do not see how people's risk profile is any different than what it was before Dec 2019.

Flu, I believe, is most contagious when you’re feeling ill. That’s one huge difference between this pandemic and just your typical flu.

You can’t isolate if you don’t know you’re sick.

That does seem to be changing now that we've all been vaccinated, though. It seems that training your immune system to recognize the virus leads to symptoms developing earlier in the course of disease, below the ~10^6 copies/mL threshold a rapid test can detect. I don't know if everybody who is vaccinated is getting early symptoms but anecdotally it seems to be pretty common.

Two reasons, IMO.

  1. Things such as influenza mostly spread when the person is symptomatic.
  2. Something along the lines of 50% of covid infections are from pre-symptomatic and asymptomatic people. Self isolating when you have symptoms is certainly good, but it is by no means the entire picture.

>I do not see how people's risk profile is any different than what it was before Dec 2019.

There are virtually zero deaths attributable directly to flu by hospitals. The vast majority are imputed by estimated excess deaths.

So even by completely different and unfair metrics, covid is vastly more dangerous. If you went by that standard covid likely has claimed over a million US deaths already, compared to a few tens of thousand for flu.

https://www.cdc.gov/nchs/nvss/vsrr/covid19/excess_deaths.htm

On top of that, covid has a significantly higher R0 value, which means you’re much, much more likely to come into contact with it.

That’s how you change your risk calculation: it’s the cost of getting it (probability of death or maiming) times the probability of getting it (community spread level and nasal viral shedding rate). There is no mitigating factor here wrt covid vs flu risk.

The crazy thing is that those other viruses are more serious for kids than covid.

if there is a reason for the mass testing, because it doesn't really let you know anything except whether or not you have COVID

If you test positive, you're supposed to stay home and isolate so you don't spread COVID.

Tests aren't perfect, since as you said, there seems to be a significant false-negative rate with Omicron, and you can be contagious before you show symptoms, but the tests help prevent people from spreading confirmed cases, and can be helpful to pre-test before you spend time with someone who is at high risk for COVID.

> Tests aren't perfect, since as you said, there seems to be a significant false-negative rate with Omicron

Its not even Omicron. Rapid tests always had something like a 40% false-negative rate or something stupidly high.

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That's why you're supposed to take two tests if you're asymptomatic, to reduce the chances of a false-negative.

Fortunately, the false-positive rate is less than 5% IIRC, and fairly reliable.

EDIT: Sensitivity and Selectivity isn't really false-negatives or false-positives. But for the purposes of this discussion, its probably good enough. Besides, I'm just an ignorant programmer who doesn't know the difference between them.

I'm just going by what the FDA said:

https://www.bizpacreview.com/2021/12/29/fda-says-rapid-at-ho...

“RADx recently performed preliminary studies evaluating the performance of some antigen tests using patient samples containing live virus, which represents the best way to evaluate true test performance in the short-term. Early data suggests that antigen tests do detect the omicron variant but may have reduced sensitivity,” according to the FDA.

I'm sure. But the sensitivity of rapid tests were always much much worse than the sensitivity of PCR tests. The original sensitivity of rapid tests were like 60%.

Frankly, going from 60% to 40% doesn't change my viewpoint on rapid tests. Its all "unreliable false negative" to me (I don't know what it is for Omicron, I'm just pulling 40% out of nowhere). But whatever it was, the sensitivty was always so low that you never could rely upon a negative-reading, due to the high chance of false-negatives.

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Rapid tests remain useful, but you _MUST_ always be mindful of their high false negative rate. The fact that their "unreliable stat got even more unreliable" isn't really news, because you shouldn't have been relying upon it anyway.

The most recent guidance says isolate for 5 days, then go back to work if you want to, or optionally take another rapid test and if it's still positive, isolate for another 5 days. The CDC also acknowledges that the virus is transmissible for 10 days after symptom onset. These "shoulds" and "supposed tos" are being thrown out the window. Health care workers in CA can go back to work immediately following a positive test if their symptoms aren't severe and in many cases they're being asked to.

Its all about tradeoffs.

Rapid tests give you a result within 15 minutes. PCR tests you gotta ship to a lab, and wait maybe 2 or 3 days before they report back to you.

I think PCR tests (which nominally take 15 minutes) are the best. But we clearly don't have the infrastructure to support it. Every lab doing PCR tests is going at full throttle and yet we still have this 2 or 3 day delay everywhere.

Meanwhile, at-home rapid tests work immediately. They're way less accurate, but its better to have some degree of testing rather than nothing at all.

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Lets say you have a workforce consisting of 10 people who are sick with COVID19 right now. PCR tests might catch 9/10 of those people. Rapid tests might only catch 6/10.

But removing those 6-people with Rapid tests in your workforce will slow down the spread. 4-people spreading COVID19 in your workplace is better than 10-people spreading COVID19.

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EDIT: More importantly, Rapid tests will catch those 6 people _TODAY_. PCR tests will take ~3 days before they report back, meaning if you're on PCR-tests only, your COVID19 positive people will be around the workforce for 3 days.

If you use both Rapid Tests + PCR tests, you remove those 6 people _TODAY_ from the workforce (meaning 4 people will be spreading COVID19 in your workforce). 3 days later, those 3 other people are removed which is "too late". The Rapid test was in fact more useful.

PCR tests are better for contact tracing, due to their higher reliability. If someone tests positive with PCR tests, you trace their contacts and tell _THOSE_ people to get PCR tests and/or rapid tests, in an attempt to "get ahead" of the disease. (IE: those 3 people who weren't caught by rapid tests were in contact with 15 people total. You now tell those 15 people to rapid test + PCR test).

I think the point is that rapid tests are performing significantly worse now on Omicron than they were for prior variants.

I'm going to "vouch" your post, because its a fine point even if I disagree with it.

Rapid tests _always_ had bad sensitivity. Its gotten worse for Omicron, but going from "bad" to "worse" isn't really a big deal, because you never should have been relying upon negative test results anyway.

That's my point. The "use" of rapid tests was their "rapid" nature, coming back with a result in 15 minutes is way better than waiting for 3 days. The PCR is needed if you want to truly rely upon the result (well, kinda sorta. PCR got better sensitivity / specificity but its still not perfect).

This comment misses that false-positive and false-negative rates are wildly different.

The rapid tests are still quite useful because a positive test is very reliable and saves you several days of waiting for PCR results.

Perhaps the test results should be labeled "Yes, you have covid", and "meh, not sure".

My symptomatic, boosted SO received 4 negative nasal-swab PCR tests (1 day apart each), given by a nurse, before finally testing positive on the 5th test. Seems totally unreliable

so, in that case, which test was the error? negative or positive?

seems like she has covid ¯\_(ツ)_/¯

Can I ask why you would be so insistent on testing? Did you change treatment based on a positive test result?

When my son tested positive, they refused to let us re-test to see if it may have been a false positive. He's 2 and was completely asymptomatic.

In our area, when kids test positive, they don't have to be tested for many weeks after. I know several that tested positive a few weeks before Omicron hit, then were refused when they eventually had Omicron symptoms.

SO insisted on the testing, not me, because she works around a lot of other people and children and did not know if she was contagious.

She also thought it would be helpful to know if exposure = any additional immunity down the road, since all of the facts constantly change

PCR false negative rate is really low.

There are other possibilities like that she had a cold and the 5th test was a false positive or she had a cold and got covid several days later.

There are a few news stories out there indicating that because Omicron grows better in the throat that also swabbing the throat helps reduce false negatives. Though the official word would be to not do this since the tests were officially only developed tested with nasal swabbing.

It's worth noting that rapid test results roughly align with contagiousness, which makes them an excellent tool to fight the spread of this thing. [1] (See the 2nd image on this page).

PCR tests will report COVID infections that are way below the threshold of transmissibility, and they'll keep reporting positive results long after the infected person is no longer contagious.

"Am I contagious?" is arguably a more useful question to answer than, "Do I have any detectable amount of COVID in my body, at all, using the best laboratory testing processes available?"

[1] https://yourlocalepidemiologist.substack.com/p/antigen-tests...

I my country they did a (pre-omicron) comparitive study, testing people with PCR and giving them an antigen test to use at home [1]. There they found a false-negative rate of 16% (sensitivity 84%) for symptomatic people with high viral load, which is a proxy for contagiousness. For people without symptoms false-negative rate was 77% (sensitivity 23%). Not that great.

[1] https://www-umcutrecht-nl.translate.goog/nieuws/corona-zelft...

The answer is probably something along the lines that it's not a magic bullet but 1.) There's a lot of political pressure to do "something" and tests are one of those things and 2.) Whether useful or not testing is required either literally or people want it for the peace of mind (illusory or not) so lack of tests is a headache.

> a reason for the mass testing

Covid is much more dangerous for the elderly than the young, even vaccinated. The young are so safe that there have been ~250 total covid deaths in the US age 0-4.

Also, there is growing evidence that the lateral flow tests correlate well with being infectious.

Testing reasons:

For lots of staff (medical, school, factories), to avoid unnecessary prophylactic isolations, particularly for people whose work cannot be done remotely. And for the same group of people, testing daily (were we in a competent country with the test manufacturing to support) could significantly reduce community spread. Daily tests are infeasible to do with pcr if for no other reason than the reporting lag.

For visiting high risk people: reasonably reliable, fast indicator of whether you have covid in order to make near realtime decisions about activities to engage in. Like masks, this will reduce community spread.

I too am beginning to wonder the efficacy of the tests, which if true may point to a higher infection rate, but, possibly, a lower morbidity rate.

From what my pharmacist told me a fair bit of the kits can't detect omnicron reliably. The ones that do seem to have about a 7-10% failure rate. He suggested doing two or even 3 kits at once or space them out over a couple of hours to decrease the chance of a false negative.

The person selling you tests says you need to use more of them than is recommended?

Tests aren't statistically independent events. Taking multiple rapid antigen swabs doesn't improve their accuracy. Multiple tests spaced out over a few days does.

> I am starting to wonder at the efficacy of the tests and is it that they just can't catch Omnicron as well? Are my kids really just sick with some other random thing despite dozens of people in our social circle getting COVID?

My understanding is:

1) Existing rapid tests are not as sensitive to Omicron as previous variants.

2) Negative results on rapid tests are unreliable, especially single negatives. They're more reliable when taken in series, and the instructions for the ones tell you to take two tests, 3 days apart. However, their positive results are very reliable, so if only 75% of the positive people who take one actually test positive, you've still successfully detected 75% of those infections.

PCR tests are far better at detecting infections early.

With this variant, the tests seem mainly about "how much longer should I quarantine?" It's test two or that finally shows positive, after you're pretty sure it's COVID.

why even test? if you test positive who are you saving from exposure? everyone is getting exposed to omicron regardless.

The only logical explanation for testing I can fathom is to use as an excuse to get time off work and/or social approval among peers.

I have a friend at a workplace who setup a different bucket to bill time off for COVID against than regular sick days. That would be one reason.

I'm full on board the "let'r rip" train, but don't knowingly expose people to sicknesses. Even if they'll get it eventually, it's better if everyone doesn't get it all at once.

What kind of tests? There are two types with very different characteristics, and it's good to specify which kind of test you're talking about.

> Are my kids really just sick with some other random thing despite dozens of people in our social circle getting COVID?

If you are in the US, flu is a possibility. Unlike 2020-21, the 2021-22 flu season is coming on strong: https://www.cdc.gov/flu/weekly/usmap.htm

I am really surprised I haven’t heard anyone talk about false positive rates, false negative rates, or bayes’ theorem since covid tests first became available. I mentioned it to family when the stories of conflicting tests showed up on the news and they balked at the idea of using math…we are very different people, my family and I lol

I took a self test after having symptoms and it was positive so I just isolated myself instead. I skipped doing an official test because just as you said it does not provide any relevant information to me other than what I already know.

People like myself would act very differently to a cold than COVID. It changes also needs to isolate/quarantine, and helps us get a handle on asymptomatic cases who otherwise would go around continuing to infect others.

> helps us get a handle on asymptomatic cases

This won't help us get a handle on asymptomatic cases - to do that, we'd have to be able to test everyone on a frequent and consistent basis.

This program doesn't even cover one test for everyone in my house, let alone weekly or more frequent testing. And aside from this, I have to spend hours looking for any available rapid tests to buy around here, and if/when I have some, I can't afford to use them on randomized or even weekly testing.

The rapid tests have a very high false negative rate regardless of variant, but a very low false positive rate. They should not be trusted as proof that you do not have COVID, only as proof that you do have it.

I think you can generally reasonably be sure that you dont have it if you test negative on a rapid test, especially if you take multiple. The accuracy of the better ones (which is what we're getting in the US) looks to be about 80% for people who do have the virus. To me, you can trust that to say you dont have covid, especially if youre vaccinated.

For evidence that completely supports this downvoted comment, this is from the documentation of the self-test kit that I have:

> QuickVue At-Home OTC COVID-19 Test correctly identified 83.5% of positive specimens and 99.2% of negative specimens.

Does every submission related to covid have to be an opening for a HNer to recount a personal anecdote about how a thing being done to try and reduce covid spread is questionable?

My post was put in earnest because I am really trying to understand, I live in an area that is pretty much of one mind and believe that the best way to try and work through some of the division we are facing in this country is to understand and listen to the perspective of others. Even if I don't agree, trying to hear the other side may make me aware of considerations and factors I was unaware of before.

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