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The sensitivity of PCR tests to SAR-COV-2 varies over time from time to infection. I think the the OP is overestimating how narrow this window is though. It's n
by icegreentea2 7y ago
The sensitivity of PCR tests to SAR-COV-2 varies over time from time to infection. I think the the OP is overestimating how narrow this window is though. It's not like you need to test within a few days or a week to be positive - it's just that viral load is maximum for only a few days (roughly the +/-3 days around onset of symptoms).
Even after the viral load in the upper respiratory tract drops off, there's still lots of virus around. You'll likely test positive -1/+2 weeks around onset of symptoms.
- darkerside 7y agoDepending on the nature of the virus and how the PCR test works with it, I couldn't rule out that it could be much longer than that. Virii are not my area, but there are bacterial diseases that result in positive PCR years after infection. Disclaimer: microbiology is also not my area.
- icegreentea2 7y agoYes, it all depends on how the agent infects the body and how the immune system is able to clear it. Our belief (based on how other coronaviruses behave) is that the body is pretty good at clearing it out, and that the virus doesn't really have a mechanism for forming a reservoir within the body. The expectation is that PCR negative is roughly correlated with fighting off the disease in the short term, and basically perfectly correlated in the long term.
- djsumdog 7y agoIs this test sensitive to just SARS-CoV-2? What is the possibility that other corona viruses (like the ones that cause many of our colds) could create a false positive? I haven't heard anything from a reliable source on that.
- tim333 7y agoPCR is pretty selective for SARS-CoV-2
- gridlockd 7y agoI'm trying to figure out what tests they used. PCR is very specific but only works reliably in the early stages and generally has a high false negative rate. Antibody tests only work after several days of infection, but some of them are not very specific to SARS-CoV2 and therefore have a high false positive rate. So you really need use both tests, but you can't just OR the results together, because then a faulty antibody test will massively skew the results upward.
- KaiserPro 7y ago> but only works reliably in the early stages No, it only works if there is enough virus to be detected. If you are infected, you will have a high enough count to be detected. Each type of PCR test is highly selective. The point of them is that they can differentiate between many types of virus, depending on how its setup. > Antibody tests only work after several days of infection Yes. Depending on the type of test, and how its done. it can be up to a month before these tests are accurate.
- gridlockd 7y agoIn principle yes, but The PCR test is usually a throat swab, where detectable amounts often disappear after a few days, even in severely symptomatic cases. This is the reason why China started to accept clinical diagnosis like chest scans, causing a sudden big spike in cases.
- yaur 7y agoIs there a source that says they were using PCR testing? The article seems pretty light on technical details.