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Hi all, Connecticut is wondering how states are handling antigen results that are determined or assessed to be "false positive." The common scenario for us is the asymptomatic person (without known exposure, so low pretest probability) who had an antigen test that is positive and then subsequently gets one (or many) PCR results that are positive. Are these antigen results still counted as probable cases? We are considering *not* counting these as probable if the additional clinical investigation or information is provided that supports the test being a false positive.
Comments & Events
Tom Haupt
Lynn did you mean subsequent PCR tests were “negative”?
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Brian Erly
In Colorado, we treat all positive rapid tests as "probable" cases, regardless of future negative PCR results. A subsequent positive PCR result would change the case to a "confirmed" case. As you said, this raises the possibility of false positive rapid results causing isolation/quarantine for people who never really had COVID. But the specificity of these tests seems a little better than the sensitivity, even in the UCSF real-world study of the Binax: https://www.ucsf.edu/news/2020/10/418761/rapid-covid-19-test-shows-promise-community-test-setting
For us, a bigger concern has been false negative rapid tests. We've been working to see if we can come up with an algorithm that will satisfactorily capture community incidence and individual risk to guide interpretation of rapid tests. This is where we are after some preliminary talks, and I'm curious if any other states have put together something similar:
Yes, we are actively discussing and I think would be good to discuss on an upcoming CSTE call (not sure which one - ideas?).
Our thoughts so far: If there is a pos antigen with negative PCR within 2 days (plus or minus) Consider false positive IF no known exposure to a positive case, and Either 1) Asymptomatic, or 2) Symptomatic but clinician/med epi feel clinical scenario more likely to be a different diagnosis (esp Flu, RSV)
We may decide that pos Flu/RSV with neg COVID PCR would also make us consider pos Ag a false pos.
People here so far are not comfortable considering a neg PCR by itself enough to rule out the case without SOME clinical or exposure info.
These are tough!
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Richard Danila
We agree with Annie's (NYC) thoughts and are following that. But operationalizing this with 1,200 to 2,300 new cases coming in every day (albeit only 20 or so positive antigen tests) is very difficult.
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Annie Fine
Agree volume of data is a big issue and managing the data in real time is also very challenging. Right now all positive antigens get sent to our contact tracing program so people get isolated - then it will take time to determine that it was a false positive... and by then contacts are elicited and quarantined etc. Lots of redundant/unnecessary work! One idea was to impose a lag on initiating contact tracing until we can process all the data but this is problematic due to the lags in reporting negative PCRs. Huge headache.
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Jeff Engel,Senior Advisor for COVID-19
Also, working with AHCA, we learned that some LTCFs using Ag screening tests (asymptomatic) were cohorting Ag-positive residents into COVID units only to discover later the false positive result, but too late as the resident became infected on the COVID unit as a result of the transfer. So primum non nocere: asymptomatic, Ag-positive LCTF residents should be isolated in-place and transferred to a COVID unit only after PCR confirmation.
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Lynn Sosa
Thanks all! I did mean subsequent PCR tests are negative after the positive antigen.
Yes I think this would be a great discussion for us to have! Also not sure the right call though--Jeff?
Our thoughts so far:
If there is a pos antigen with negative PCR within 2 days (plus or minus)
Consider false positive IF no known exposure to a positive case, and
Either 1) Asymptomatic, or
2) Symptomatic but clinician/med epi feel clinical scenario more likely to be a different diagnosis (esp Flu, RSV)
We may decide that pos Flu/RSV with neg COVID PCR would also make us consider pos Ag a false pos.
People here so far are not comfortable considering a neg PCR by itself enough to rule out the case without SOME clinical or exposure info.
These are tough!
Yes I think this would be a great discussion for us to have! Also not sure the right call though--Jeff?