It looks to me like the first study Jetelina cites agreed with me? Average time to positive antigen test was 3 days after positive PCR. Everyone developed symptoms within 2 days of the positive PCR (which is surprising in and of itself), and at least 4⁄30 people spread covid before getting a positive antigen test, which presumably would have been higher if they didn’t have the PCR to warn them. PCR is more sensitive than cue tests so this doesn’t translate directly, but I consider it to bolster the case against preemptive antigen testing being useful.
In the second study, which was on demand not preemptive testing, antigen tests detected 50% of PCR positives. If I understand your claim correctly, it’s that the PCR+/antigen- people aren’t very contagious? I agree that antigen+ people are on average more contagious, but since symptomatic people (should) stay home, I don’t think that’s the right reference class. The meaningful work is done identifying people who couldn’t otherwise be identified as infectious.
I think it’s important to emphasize that antigen+ people are much more contagious than antigen-. It’s hard to quantify that, but based on typical differences in Ct value, it’s probably a very substantial difference (factor of 10+?).
You’re absolutely right that the reference class is the key issue (if there’s one thing I’ve learned from hanging out with epidemiologists, it’s that they’re always grumpy about people using the wrong denominator).
In a perfect world, where everyone with any symptoms whatsoever stayed home and was scrupulous about following what the CDC exit guidance ought to be, antigen tests would be significantly less useful. But in the real world, people absolutely go out when they have mild symptoms. That’s advocated for in the comments right below this, which are from people who are presumably much more conscientious than average.
IMHO, the biggest value of antigen tests is in catching people who are mildly symptomatic but think it’s just allergies / they had a negative test last week so it can’t be covid / they’re probably over the worst of it. Within my (not enormous) extended social circle, I’m aware of two very recent cases when antigen tests flagged as infectious people who would otherwise have been out and about despite having mild symptoms.
This is kind of OT, but I’m going to ask anyway: under what conditions do you think that symptomatic people should stay home? If a person’s symptoms are debilitating, staying home is the obviously correct choice. But if a person’s symptoms aren’t debilitating and wears a ventless respirator (and can tolerate it and it doesn’t interfere too much in what they’re doing), I don’t see why they should stay home.
In general I think people who are definitely sick should not go to parties or the social part of work (which for almost everyone I know is the part that can’t be done from home), even with ventless respirators, even with a negative covid test. There are lots of diseases, spreading them is costly, masks interfere too much at parties and in person interactions at work, which is the only reason for many people to go (if you’re at a job that benefits from in-person presence because of equipment or because your home is too disruptive, this doesn’t apply. if your job involves interacting with a lot of people, or food, obviously don’t go while symptomatic). I think running unpostponable maintenance tasks like grocery shopping (if you can’t get delivery) or doctors visits is okay.
The problem I find harder is people who are mildly symptomatic, in ways that could be an illness or allergies, or are on the trail end up symptoms after a disease has probably but not definitely been cleared. “No interaction for five days after a sniffly nose” is life ruining for a lot of people.
The problem I find harder is people who are mildly symptomatic, in ways that could be an illness or allergies, or are on the trail end up symptoms after a disease has probably but not definitely been cleared. “No interaction for five days after a sniffly nose” is life ruining for a lot of people.
Yeah, this is a much more difficult situation for me. I think I more or less always have minor COVID symptoms if construed strictly, given that various minor allergies or similar have the same symptoms as COVID...
Decreased social interaction can be a showstopper but sometimes it isn’t; so, I think a case-by-case policy would be more reasonable than a general stay-at-home-no-matter-what recommendation. In the party scenario, the choice is between attending and not attending (I’m assuming that there’s no remote party option like VR chat or something). For some parties (like birthday parties), attending might be better even if social interaction is reduced. For others (like indoor dinner parties), it might not be worth attending. In the job scenario, many jobs can’t be performed remotely, so physically attending would be better. You seem to have acknowledged this when you said:
if you’re at a job that benefits from in-person presence because of equipment or because your home is too disruptive, this doesn’t apply
Apologies for poor formatting, I’m on mobile.
It looks to me like the first study Jetelina cites agreed with me? Average time to positive antigen test was 3 days after positive PCR. Everyone developed symptoms within 2 days of the positive PCR (which is surprising in and of itself), and at least 4⁄30 people spread covid before getting a positive antigen test, which presumably would have been higher if they didn’t have the PCR to warn them. PCR is more sensitive than cue tests so this doesn’t translate directly, but I consider it to bolster the case against preemptive antigen testing being useful.
In the second study, which was on demand not preemptive testing, antigen tests detected 50% of PCR positives. If I understand your claim correctly, it’s that the PCR+/antigen- people aren’t very contagious? I agree that antigen+ people are on average more contagious, but since symptomatic people (should) stay home, I don’t think that’s the right reference class. The meaningful work is done identifying people who couldn’t otherwise be identified as infectious.
I think it’s important to emphasize that antigen+ people are much more contagious than antigen-. It’s hard to quantify that, but based on typical differences in Ct value, it’s probably a very substantial difference (factor of 10+?).
You’re absolutely right that the reference class is the key issue (if there’s one thing I’ve learned from hanging out with epidemiologists, it’s that they’re always grumpy about people using the wrong denominator).
In a perfect world, where everyone with any symptoms whatsoever stayed home and was scrupulous about following what the CDC exit guidance ought to be, antigen tests would be significantly less useful. But in the real world, people absolutely go out when they have mild symptoms. That’s advocated for in the comments right below this, which are from people who are presumably much more conscientious than average.
IMHO, the biggest value of antigen tests is in catching people who are mildly symptomatic but think it’s just allergies / they had a negative test last week so it can’t be covid / they’re probably over the worst of it. Within my (not enormous) extended social circle, I’m aware of two very recent cases when antigen tests flagged as infectious people who would otherwise have been out and about despite having mild symptoms.
This is kind of OT, but I’m going to ask anyway: under what conditions do you think that symptomatic people should stay home? If a person’s symptoms are debilitating, staying home is the obviously correct choice. But if a person’s symptoms aren’t debilitating and wears a ventless respirator (and can tolerate it and it doesn’t interfere too much in what they’re doing), I don’t see why they should stay home.
In general I think people who are definitely sick should not go to parties or the social part of work (which for almost everyone I know is the part that can’t be done from home), even with ventless respirators, even with a negative covid test. There are lots of diseases, spreading them is costly, masks interfere too much at parties and in person interactions at work, which is the only reason for many people to go (if you’re at a job that benefits from in-person presence because of equipment or because your home is too disruptive, this doesn’t apply. if your job involves interacting with a lot of people, or food, obviously don’t go while symptomatic). I think running unpostponable maintenance tasks like grocery shopping (if you can’t get delivery) or doctors visits is okay.
The problem I find harder is people who are mildly symptomatic, in ways that could be an illness or allergies, or are on the trail end up symptoms after a disease has probably but not definitely been cleared. “No interaction for five days after a sniffly nose” is life ruining for a lot of people.
Yeah, this is a much more difficult situation for me. I think I more or less always have minor COVID symptoms if construed strictly, given that various minor allergies or similar have the same symptoms as COVID...
Decreased social interaction can be a showstopper but sometimes it isn’t; so, I think a case-by-case policy would be more reasonable than a general stay-at-home-no-matter-what recommendation. In the party scenario, the choice is between attending and not attending (I’m assuming that there’s no remote party option like VR chat or something). For some parties (like birthday parties), attending might be better even if social interaction is reduced. For others (like indoor dinner parties), it might not be worth attending. In the job scenario, many jobs can’t be performed remotely, so physically attending would be better. You seem to have acknowledged this when you said: