What’s the longest someone has tested positive on home antigen test?
January 8, 2025 6:57 PM Subscribe
How long can you test positive on a home antigen covid test (aka rapid test)? A nurse told me that people can still test positive on home antigen tests for three months (and it not be a new infection, and not be contagious) - that’s certainly true of PCR tests, but I had not heard that about home antigen tests before. Could you direct me to factual medical citations or tell me your relevant direct personal experience if you continued testing positive on home antigen tests for two weeks or more (with it clearly being the same covid infection, not testing positive again a few weeks later after symptoms had gone away and while not testing in the mean time, where that is more likely to have been a new infection)?
Secondary question that my Google-fu is failing me for: last I read, if you were testing positive on a home antigen test, even a faint line, that would indicate being contagious (though current public health recommendations don’t care after a certain point, because most people aren’t masking in public, so there comes a point where the amount of virus you are shedding isn’t significantly impacting overall community levels or risk, so they don’t recommend testing to exit isolation anymore for example). Is that still true? Or could you have the antigen proteins that the tests detect from dead virus or virus fragments that are still just hanging around up in your sinuses (eg. if one’s particular nasal/sinus structure somewhat impedes sinus drainage)?
Secondary question that my Google-fu is failing me for: last I read, if you were testing positive on a home antigen test, even a faint line, that would indicate being contagious (though current public health recommendations don’t care after a certain point, because most people aren’t masking in public, so there comes a point where the amount of virus you are shedding isn’t significantly impacting overall community levels or risk, so they don’t recommend testing to exit isolation anymore for example). Is that still true? Or could you have the antigen proteins that the tests detect from dead virus or virus fragments that are still just hanging around up in your sinuses (eg. if one’s particular nasal/sinus structure somewhat impedes sinus drainage)?
Personal experience of 2 family members still positive until day 14 after symptom onset and well after symptoms fully resolved (had to be negative to return to work), June 2024
posted by gryphonlover at 7:14 PM on January 8 [1 favorite]
posted by gryphonlover at 7:14 PM on January 8 [1 favorite]
Here's a study from early in the pandemic (so first infections, pre-vaccine, probably not a representative sample), showing 23% positive on antigen tests for 14 days or longer (since onset of symptoms or first positive test) and a few 21+ days, with the longest being 31 days. I'm sure that's far less common now.
I'm sure it would be possible for a person to have a chronic infection for three months or even longer and to continue to test positive for that reason, but it would be very rare. It sounds likely that your nurse was just confused or misspoke.
It's also possible to have some antigen in your saliva or mucus but not be shedding any appreciable amount, but I think there is still a fair bit of debate about how common that might be (and debate about whether antigen can hang around for a significant length of time without active viral replication). In general, RAT positivity is pretty well correlated with infectivity.
posted by ssg at 7:36 PM on January 8 [1 favorite]
I'm sure it would be possible for a person to have a chronic infection for three months or even longer and to continue to test positive for that reason, but it would be very rare. It sounds likely that your nurse was just confused or misspoke.
It's also possible to have some antigen in your saliva or mucus but not be shedding any appreciable amount, but I think there is still a fair bit of debate about how common that might be (and debate about whether antigen can hang around for a significant length of time without active viral replication). In general, RAT positivity is pretty well correlated with infectivity.
posted by ssg at 7:36 PM on January 8 [1 favorite]
Total anecdote: my friend went to 21 days once; this was in 2021 or so and was her first infection.
posted by chesty_a_arthur at 7:52 PM on January 8 [1 favorite]
posted by chesty_a_arthur at 7:52 PM on January 8 [1 favorite]
Seconding what ssg said above. A positive antigen test = infectivity. The fact that the majority of the population neither cares if they infect others nor cares if they're repeatedly infected themselves doesn't change the science.
In 2022 I tested positive on antigen tests for 54 consecutive days; I was symptomatic the whole time[1]. My entire treatment team--which grew in with every passing week as the positive tests continued--was unanimous that I was still contagious and advised me in no uncertain terms to continue self-isolating until I tested negative on an antigen test. (This was... every bit as miserable as it sounds.)
There was a near-exact correlation between the immediacy and brightness of the antigen test positive line and the severity of my symptoms. My PCR cycle thresholds increased (indicating a lower viral load) as my symptoms resolved and the antigen test positivity line faded.
[1] I’m immunocompromised from the B-cell-depleting therapy I take to manage MS which made my vaccine response subtherapeutic and made it more difficult for me to clear the virus once I was infected.
posted by jesourie at 10:02 PM on January 8 [5 favorites]
In 2022 I tested positive on antigen tests for 54 consecutive days; I was symptomatic the whole time[1]. My entire treatment team--which grew in with every passing week as the positive tests continued--was unanimous that I was still contagious and advised me in no uncertain terms to continue self-isolating until I tested negative on an antigen test. (This was... every bit as miserable as it sounds.)
There was a near-exact correlation between the immediacy and brightness of the antigen test positive line and the severity of my symptoms. My PCR cycle thresholds increased (indicating a lower viral load) as my symptoms resolved and the antigen test positivity line faded.
[1] I’m immunocompromised from the B-cell-depleting therapy I take to manage MS which made my vaccine response subtherapeutic and made it more difficult for me to clear the virus once I was infected.
posted by jesourie at 10:02 PM on January 8 [5 favorites]
To clarify, is your main question about how long an infection can last, or how long they can continue to test positive when they are no longer truly infected?
Here’s one paper looking at viral culture and RAT positivity at day 6 and later. In this study only about half of those who tested positive late in infection had positive viral culture. Tiny sample size who had culture results available, so take with a couple grains of salt.
jesourie’s comment above speaks to the possibility of true persistent infection — rare but consequential (last I heard that’s the best guess about where Omicron came from). Presumably someone in that situation could continue to test positive on antigen tests without a real upper bound.
posted by eirias at 1:25 AM on January 9 [1 favorite]
Here’s one paper looking at viral culture and RAT positivity at day 6 and later. In this study only about half of those who tested positive late in infection had positive viral culture. Tiny sample size who had culture results available, so take with a couple grains of salt.
jesourie’s comment above speaks to the possibility of true persistent infection — rare but consequential (last I heard that’s the best guess about where Omicron came from). Presumably someone in that situation could continue to test positive on antigen tests without a real upper bound.
posted by eirias at 1:25 AM on January 9 [1 favorite]
I asked about it here when I was still positive and still isolating on day 20. On the advice of late afternoon dreaming hotel, I got a PCR test, it was negative, and that meant I was no longer contagious. I tested again with the antigen test because I wanted to know if it went negative (so I’d know whether I could trust a positive in the future if I suspected Covid again). I eventually tested negative on that, too — I think it took another couple of weeks after the negative PCR.
posted by daisyace at 7:05 AM on January 9 [1 favorite]
posted by daisyace at 7:05 AM on January 9 [1 favorite]
Just anecdata to say that it happens - An elderly relative of mine had covid in fall 2023 and tested positive on rapid antigen tests for something like 52 (? if I am remembering right) days. Strong positive color for the first 40 days and then tailing off in intensity for another 10+ days. She'd had paxlovid immediately, and no fever or symptoms after the first week or two. We masked the whole time but toward the end of that time, her doctors were telling us firmly that we didn't need to mask anymore - and that we should just stop doing rapid antigen tests. I don't know if she was contagious -- my reading at that time (about what exactly the rapid antigen test is testing, and about how durable those things should be in the body) still supported the "positive antigen test is good reason to think you could be contagious" view... and there wasn't enough data on cases like this for me to be confident she wasn't. But the doctors felt confident she wasn't.
posted by LobsterMitten at 7:33 AM on January 9 [2 favorites]
posted by LobsterMitten at 7:33 AM on January 9 [2 favorites]
My last positive test was on day 15 I think? Regular old covid case otherwise but it definitely hung on.
posted by potrzebie at 8:03 AM on January 9 [1 favorite]
posted by potrzebie at 8:03 AM on January 9 [1 favorite]
Daisyace, testing negative on PCR but still positive by RA is much more likely to be caused by a failed swab for the PCR than a true negative. And a positive RA is, as you've read here, a pretty good indicator that you're still contagious. In that situation I'd believe the RA.
False positives on RA are very, very, very rare. Your PCR test was almost certainly a false negative (also rare, but a bad swab will do it).
posted by Dashy at 9:07 AM on January 9 [1 favorite]
False positives on RA are very, very, very rare. Your PCR test was almost certainly a false negative (also rare, but a bad swab will do it).
posted by Dashy at 9:07 AM on January 9 [1 favorite]
Antigen tests are infectiousness tests; if you test positive on them you're absolutely still contagious. Covid infection can be chronic. If I was infectious for longer than two weeks I'd see an infectious disease specialist who knew something more about Covid than your nurse does.
posted by shadygrove at 9:31 AM on January 9
posted by shadygrove at 9:31 AM on January 9
A relative tested positive for 17 days on home tests last year, with only mild symptoms the first day or two and then no symptoms. She knows someone who said he had tested positive for 90 days, but I don't know the details and how accurate that is.
posted by The corpse in the library at 9:41 AM on January 9
posted by The corpse in the library at 9:41 AM on January 9
I posted a couple links in a comment last August, and I'll just quote the relevant part here:
posted by fedward at 1:31 PM on January 9 [1 favorite]
A couple seemingly contradictory things are true: (1) tests may still display positive results even though the virus isn’t “replication competent”; (2) most people stop being contagious on or before the 10th day after exposure or symptom onset, but not all, and this paper notes that the end of contagiousness hasn’t adequately been studied.I haven't gone looking for any updates since August, so I guess it's possible somebody has now filled the gap pointed out by the paper in the second link, but that's a good place to start.
posted by fedward at 1:31 PM on January 9 [1 favorite]
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posted by mai at 7:08 PM on January 8 [1 favorite]