A negative rapid test should be necessary before ending isolation. The CDC’s new guidelines don’t say this but this seems overdetermined and obvious to me. If you care about not being infectious, you should check on that before exposing others.
Recovered patients: Patients who have recovered from COVID-19 can continue to have detectable SARS-CoV-2 RNA in upper respiratory specimens for up to 3 months after illness onset. However, replication-competent virus has not been reliably recovered from such patients, and they are not likely infectious.
How can a patient have a positive PCR test but not be infectious?
Reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) is the primary method used to diagnose SARS-CoV-2 infection and many other viruses. The test works by creating copies of viral genetic material in respiratory samples over many cycles. A single copy of viral RNA can be amplified to more than 2 trillion copies during a typical 40-cycle testing protocol. Amplification of genomic sequence is measured in cycle thresholds (Ct) and the Ct values correlate with whether a sample contains infectious virus particles. If the viral RNA is detected after just a few amplification cycles (i.e. at a low Ct value), that means high RNA levels are present and thus more viable virus; however, because this test is designed to be a sensitive diagnostic tool (not for monitoring disease progression), a very high Ct value (low RNA level) is set as a positive range cutoff. This means that very low levels of the RNA or viral genomic fragments can test “positive” for months after the acute infection but are not associated with live virus. This detection issue is common for other RNA viruses.
Which suggests to me that PCR testing might be prone to false positive after an infection, but does not clarify to me if Rapid Antigen Tests are also prone to false positives.
My guess is that false positives in the Rapid Antigen Test are uncommon, since the proposed causal mechanism for why PCRs give false positives is because of the viral load amplification, which does not happen with Rapid Antigen Tests.
The key question: should I end isolation after 10 days regardless of rapid antigen test result?
How common are false positives after infection?
Eg the CDC says that:
Which suggests they might be not that uncommon.
UTSouthwesterner Medical Center says that (the CDC says something similar):
Which suggests to me that PCR testing might be prone to false positive after an infection, but does not clarify to me if Rapid Antigen Tests are also prone to false positives.
My guess is that false positives in the Rapid Antigen Test are uncommon, since the proposed causal mechanism for why PCRs give false positives is because of the viral load amplification, which does not happen with Rapid Antigen Tests.
The key question: should I end isolation after 10 days regardless of rapid antigen test result?