The president of the most powerful nation on earth has now contracted COVID-19, demonstrating that anyone can catch the illness. By contracting COVID-19, he illustrates the fallacy of relying on testing in lieu of adequate social distancing and protective measures. Understanding how Donald Trump became infected provides insight into the challenges we may face as new COVID 19 testing technologies become available.
Reading the news, I am struck by the misguided reliance embodied in such statements as “Pence tests negative!” The screening program for Donald Trump and the White House staff was predicated on the false assumption that a negative finding on a COVID-19 test represents a 100% guarantee. In reality, a negative test only represents an estimate of the probability that someone is infected. The accuracy of this estimate is influenced by a variety of factors, including the sensitivity of the test used, the time elapsed since possible exposure as well as a clinical estimate of the probability of infection. After taking into consideration all these factors, the test yields an estimate that may fall far below 100% certainty.
Unfortunately, the current COVID-19 PCR tests are far from providing 100% certainty. According to one study, they are only 70 to 80% sensitive, meaning that in 20% to 30% of cases where someone has the illness, the test will yield a false negative. Furthermore, the sensitivity is highly dependent on the amount of time between putative exposure and time of testing. For example, a PCR test performed only one or two days after exposure has an almost 100% chance of missing the diagnosis. The sensitivity does not exceed 50% until Day 5, and becomes most sensitive around Days 7 to 8, dropping off from there with more time passing.
The White House policy of daily testing could reduce the errors due to timing since exposure, but would not be able to overcome the inherent problem of low 70-80% test sensitivity. Even a small probability of missing the diagnosis in any one individual on the staff would be magnified by the very high numbers of people who would come in contact with Donald Trump creating an overall high probability of infection.
I am concerned that the same flawed logic that allowed Donald Trump to become infected will hamper further efforts to contain the spread of illness. The headlines on October 2, 2020 described who has tested negative. However, if the exposure was only several days prior to testing, the negative test would not be very meaningful. These individuals would still need to maintain strict quarantine procedures to prevent further spread of the illness. I am not sure they will.
Donald Trump’s infection illustrates the need to use screening tests to augment, but not replace, infection control procedures. In an ideal world, inexpensive tests would be widely available, and everyone would be tested regularly. But we would still need our schools, workplaces, and other public spaces to use the best practices to reduce the spread of infection such as social distancing, facemasks and air filtration. Testing would represent an additional layer to detect who needs to stay home.
The recent release of Abbott Lab’s COVID-19 antigen detection test, BinaxNow, provides an important breakthrough in our ability to perform frequent surveillance screening of large numbers of people. COVID 19 PCR tests may be more accurate but they are slow and expensive. The BinaxNow assay utilizes a lateral flow immunoassay embedded in a test card (similar to a urine pregnancy test) to detect a COVID-19 antigen from a lower nasal swab in 15 minutes for about $5. While not quite as accurate as the PCR test, it can adequately identify those with a higher number of viral particles in their upper airways who are thought to be the most contagious. In August, the US government purchased 150 million tests for mass distribution. We now have the technology for mass testing to reduce the rate of COVID-19 infection by identifying the estimated 50% of cases that are asymptomatic.
With the advent of mass screening, millions of us will receive frequent affirmations of a negative test. Human nature will push us down a slippery slope… “if I am negative, do I really need to wear this mask all of the time?” I hope the case of Donald Trump will remind us that a negative test result is not 100% accurate and that test results should not deter us from careful adherence to infection control practices.
To date, we have had great statistics here in the practice. I want to encourage all of you to remain vigilant as the months drag on.
“An ounce of prevention is better than a pound of cure (which we don’t have)!”
Please let me know if you have any questions or concerns.
Barry Rotman, MD