Testing Won't Make Thanksgiving Safe!
A Same-day Test Cannot Be Relied Upon to Ensure a Safe Gathering
Having everyone get a Covid test this week will NOT make your Thanksgiving gathering safe!
The only way to manage risk for Thanksgiving is to keep the events to only people already in the household. As soon as people from outside join, the risks escalate. The entire group is only as safe as the least-safe member.
All it takes is inviting a single person who thinks masks are stupid, the virus is fake, and going to bars is a good idea and the entire group now has a risk-level equivalent to that person!
And as the White House learned after the Rose Garden super-spreader event, inviting risky people and then relying on same-day testing to keep everyone safe is a dangerous fantasy.
There are several issues with using testing to create safe events:
Time-lag between infection and when a test will show positive
Time-lag on getting test results back
High false-negative results from same-day rapid tests
Time-lag after Infection
People will test negative for SarsCoV2 for 3-5 days after the initial infection. It simply takes time for the virus to replicate to a level where it can be detected by even the most sensitive tests.
That’s generally thought to be a minimum of 3-days for a laboratory-run RT-PCR test and 10+ days for a rapid antigen test.
You can easily have gotten a negative on a test yesterday and be fully infectious to others today and still have not developed any symptoms.
Time-lag on Getting Test Results Back
Test results for an RT-PCR test generally take 2-5 days to return results. You can test today, be infecting people tomorrow, and not get a test-positive result until a couple of days later. In general, a test result will lag an infection event by a week or more.
This is especially critical if you think you’ve been exposed. NEVER wait for test results to come back, quarantine immediately.
High False-Negative Results from Same-Day Tests
Using a same-day rapid test to avoid delays in getting results back will not solve the problem either. All rapid tests have issues with very high rates of false-negatives. This means you can be fully infectious, but the test says you’re fine.
There are two categories of rapid test:
RT-LAMP (Isothermal-PCR) Tests like the Abbott ID NOW
Antigen tests like the Abbott BinaxNow lateral-flow strip test
In actual clinical practice, the RT-LAMP tests will run as high as 40% false-negative. Meaning that out of 10 infected patients tested, only 6 will be identified.
The antigen tests are even worse. In actual clinical practice, they will return 50%+ false-negative. Meaning that out of 10 infected patients, only 5 or fewer will be identified.
However, if you get a test-positive on ANY of these rapid tests, then you are 100% absolutely guaranteed to be infected and likely to be extremely infectious to others!
Always believe a test-positive and take action!
Always be skeptical of any test-negative!
Why So Many False Negatives Results?
There is a direct relationship between how fast you get results and how well a test is able to identify infections. There is simply NO free lunch…faster tests mean less sensitivity and more people will slip through undetected.
In addition, the rapid antigen tests are ONLY approved for testing fully symptomatic patients. If you’re not fully expressing symptoms of illness (fever, cough, difficulty breathing) then taking a Covid antigen test will almost always return a negative result.
As a result, none of the antigen tests have been validated on non-symptomatic patients, and none have FDA approval for use on non-symptomatic patients. They are designed only to test people who are already ill to rapidly determine whether the illness is Covid-19.
So don’t imagine that you can have everyone get an antigen test ahead of the big Thanksgiving gathering…that’s a recipe for a very unhappy Christmas!
About the author:
I am a scientist with 20+ years in the biotech industry. I currently work as a consultant with companies involved in developing molecular diagnostics platforms, including some of the key testing platforms used to detect the SarsCoV2 virus.
So I bring an insider’s perspective that is scientifically oriented but directed to a general audience trying to make sense of the conflicting stories surrounding the Covid pandemic.
To learn more: https://www.linkedin.com/in/dalewharrison/
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