Post infection, pre-positive test spread risk

1,129 Views | 11 Replies | Last: 3 yr ago by DadHammer
Legend
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AG
I understand that a person who gets Covid is not normally contagious for a period of a couple days. People are considered to be most contagious about 24-48 hours before symptoms. People can test negative post-exposure but still end up positive b/c they test too early and the virus is not yet strong enough to show up on a test.

So is it generally accepted that during this early period post exposure/infection when a person tests negative that they are not yet infectious?


Here's the basis for my question. A co-worker had a meeting with a guy yesterday. This guy's wife tested positive today. The guy tested negative today but let my co-worker know about his wife. I realize the guy may in fact have it and later be positive. But, is it not the case that the guy most likely did not spread it to my-coworker? If he is not strong enough to test positive, he's not likely to have spread it.


Aggie95
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I think it's generally the oppisite...a lot of people spread it pre-symptoms.
jopatura
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The guy probably didn't spread it to the coworker. CDC would likely consider the coworker a close contact of the guy.

But why did the guy end up getting tested? Is he feeling bad enough to warrant a test or was it just because his wife was sick? Was it a rapid test? If the wife is showed symptoms then tested positive, I wouldn't necessarily trust a rapid test for her husband. Rapid tests are most wrong in your exact situation. I would also ask when exactly she started showing symptoms versus getting tested to understand the risk. If she's had cold/allergy symptoms for a few days before it got bad enough to test, that adds to the risk factor for your coworker.
Legend
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jopatura said:

The guy probably didn't spread it to the coworker. CDC would likely consider the coworker a close contact of the guy.

But why did the guy end up getting tested? Was it a rapid test? If the wife is showed symptoms then tested positive, I wouldn't necessarily trust a rapid test for her husband. Rapid tests are most wrong in your exact situation. I would also ask when exactly she started showing symptoms versus getting tested to understand the risk. If she's had cold/allergy symptoms for a few days before it got bad enough to test, that adds to the risk factor for your coworker.
She had a cough last night. First symptoms. She had a meeting today so went to get a test this morning to be safe. The husband had/has no symptoms. He only tested b/c she tested positive.
Legend
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Aggie95 said:

I think it's generally the oppisite...a lot of people spread it pre-symptoms.
I understand that. Supposedly most infectious 24-48 hours pre-symptoms. My question was a little different. You are also supposedly not contagious for 2-3 days post exposure. I assume that if you are in the 24-48 hours pre-symptom but highly infectious that you would test positive.
jopatura
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Legend said:

jopatura said:

The guy probably didn't spread it to the coworker. CDC would likely consider the coworker a close contact of the guy.

But why did the guy end up getting tested? Was it a rapid test? If the wife is showed symptoms then tested positive, I wouldn't necessarily trust a rapid test for her husband. Rapid tests are most wrong in your exact situation. I would also ask when exactly she started showing symptoms versus getting tested to understand the risk. If she's had cold/allergy symptoms for a few days before it got bad enough to test, that adds to the risk factor for your coworker.
She had a cough last night. First symptoms. She had a meeting today so went to get a test this morning to be safe. The husband had/has no symptoms. He only tested b/c she tested positive.


If it was a 15 min rapid test on the husband, I would consider the coworker exposed. If the husband can come back with a negative PCR test I'd feel more comfortable with it.
Legend
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Thanks for the responses. I don't follow this stuff that closely. What's the issue with the rapid test?

jopatura
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Legend said:

Thanks for the responses. I don't follow this stuff that closely. What's the issue with the rapid test?




It doesn't detect the viral load at a low enough level. Really only useful to confirm you have it after you show symptoms. False negatives are very common.
Legend
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But doesn't a low viral load also suggest no infectivity. Wasn't a criticism of some of the PCR tests that they didn't set the cycle thresholds too high so you had a lot of people who were testing positive, but not actually infectious due to low viral loads?
jopatura
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Not always. My impression from the rapid tests is that the viral
load is high enough to be contagious but not high enough for the test to catch until they show symptoms. The other question that needs to be asked is if they thought they were exposed together or her separately. If separate the coworker is probably okay.
Legend
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Great. Thanks so much for the info.
cc_ag92
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I can't explain the reasoning behind it, but one of my coworkers tested negative last week with the rapid test, but the doctor told her she still had to quarantine until the PCR test came back because the rapid tests give false negatives regularly. She was pretty shocked.
DadHammer
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Legend said:

But doesn't a low viral load also suggest no infectivity. Wasn't a criticism of some of the PCR tests that they didn't set the cycle thresholds too high so you had a lot of people who were testing positive, but not actually infectious due to low viral loads?

100% correct
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