Today’s entry: I am hearing more and more people tell me they have tested positive then it turns out that it was a false positive. One colleague had told me that he has received 5 false positives. How does this happen and how is it impacting the positivity rate?
Bottom Line: Your question reminds me of one of the wildest days of my life. On a fall morning in 1991, I woke up with a debilitating migraine. Light, sound, and movement brought about excruciating pain and nausea. It was the worst in what had been a growing trend of migraines I’d experienced. That morning my mom took me to the ER and shortly thereafter I was being prepped for emergency brain surgery. Yes, it escalated about that quickly. The reason? A brain scan showed a mass behind my right eye so severe it required immediate action. As I was being transferred to the medical facility where I was to be operated on, I was prepped with several drugs, after that, a lot of the details are foggy for me but the long and short of it is that at least one of them did the trick to reduce the pressure I’d been feeling and I began to feel considerably better. Once I arrived at the surgery center, they took another brain scan and were shocked to see that the mass had mostly dissipated. Clearly, this wasn’t a tumor that needed to be removed as they’d originally diagnosed. Instead, I was allergy tested and found to have numerous allergies including a severe allergy to ragweed. It was an especially bad ragweed season in Atlanta, and as a football player, I was in the middle of it daily. Instead of brain surgery, I ended up on allergy shots for the next few years. You might be wondering what my story has to do with COVID testing. The point is this. As good as medical science is and can be, it can also be inexact enough to diagnose a severe allergic reaction as a brain tumor. In that context, false-positive COVID tests are perhaps more understandable.
There are two types of COVID tests. Those which sample for RNA, or ribonucleic acid, which contains one’s genetic responses for viruses among other info. The other is the antibody test which detects whether antibodies developed in response to combating the virus. Both are highly accurate but not perfect. According to a study in the medical journal The Lancet, swab tests for RNA, have had a minimum margin of error of 0.8% and a maximum of 4%. The current antibody tests (Abbott) are 98% accurate according to the FDA. Both highly accurate but obviously not perfect. For that reason, it’s possible that one person who is regularly tested may produce multiple false positives. Especially if one’s immune response to something other than COVID was similar enough to COVID that it could fool the tests based on what they’re looking for.
As for how it’s impacting positivity rates. Over the past week, Florida has averaged 2,703 new cases daily. With an average 2% error rate that’s 54 false positives daily for a total of 14,833 total false-positive cases in our state alone since testing began. In terms of the positivity rate itself. It’s not even worth discussing at this point. The positivity rate has spiked recently because the demand for testing statewide has fallen by more than half in 65 of Florida’s 67 counties over the past two months. The positivity rate is currently higher than it was in August when more than double the number of daily cases was occurring because of the general lack of demand for COVID testing. Hopefully, you and your collogue stay healthy and that explanation effectively addressed your questions.
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