Great to see the FDA expanding their requirement for serial testing using antigen tests. https://www.fda.gov/medical-devices/safety-communications/home-covid-19-antigen-tests-take-steps-reduce-your-risk-false-negative-fda-safety-communication
Some things still seem quite confused here though: 🧵 [1/10]
Guidelines to test 3 times over 4 days makes a lot of sense. Hopefully this will result in more useful test packaging in the US. https://x.com/RickByersLab/status/1545531974776983553
But what is the guideline on when to START testing after exposure? After infection, the virus “latent” (replicating but not shedding) for the first 2-3 days, maybe up to a week or more. Testing on only day 0, 2 and 4 after exposure would give a dangerous false sense of security!
The cited study does a great job of tracking individuals over time and excluding those with prior infection in order to focus just on the onset of infection (avoiding the all-too-common post-contagious-period bias in similar studies). https://www.medrxiv.org/content/10.1101/2022.08.05.22278466v1.full
But it treats “is currently infected” as the only data point of value, perpetuating the terrible idea that home use tests are for “detecting an infection” rather than the public health goal of minimizing the risk of onward transmission. In contrast see: https://x.com/RickByersLab/status/1561470940109733890.
What does the FDA even mean when they say “infected”? Eg. they say “Molecular COVID-19 tests are generally expected to detect the SARS-CoV-2 virus at least 95% of the time when someone is infected”. But with a latent period of >2 days, this is likely mathematically impossible!
I think maybe when the FDA says “infected” they mean “shedding RNA as detectable by PCR”, a circular definition! This is what has led to all the confusing and flawed reasoning evaluating antigen tests that @michaelmina_lab has been fighting against for years.
The overall message still reads like antigen tests have poor performance (especially for asymptomatic people) while lab PCR tests are perfect. Why doesn’t anyone talk about all the false negatives that occur in lab PCR tests performed during the unpredictable latent period?
The message should be: “Since there is variability in time from exposure to becoming contagious and since no test is perfect, repeat testing over days 3-7 after exposure is necessary in order to conclude an individual is not likely to become contagious.”
And also “Testing after the onset of symptoms or with a molecular test (instead of an antigen test) can help reduce this window of uncertainty by a day or two, but not eliminate it.” [10/10]
