Numbers Don’t Lie? – Understanding Coronavirus Testing in the United States

By Bence Takács

While many states are struggling to reopen their economies in the US during this highly politicized pandemic, one would think that in order to draw unbiased conclusions, the only thing we must do is to take a look at factual, raw data. However, just looking at the numbers is not enough to get the whole picture in this case, we also have to know the meaning behind them. Getting the right metrics in a pandemic is extremely important, as it can determine the way forward by giving scientists fundamental information for understanding a new virus.

In order to dig deeper in this issue, first we have to make ourselves familiar with the two types of corona virus tests – at least understanding the very basics of them. Since not everyone of us holds a medical degree in microbiology, most of us have to rely on experts’ opinion and the information publicly available published by credible sources.

According to the CDC (Centers for Disease Control and Prevention) website, the first type of test is a so-called viral test, which tells you whether or not you have a current infection. This type of test is based on a fairly straight forward concept using a swab from the inside of your nose, to tell you if you currently have an infection with SARS-CoV-2. These tests provide a highly reliable measure and some of them are point-of-care tests, meaning results may be available at the testing site in less than an hour. When it comes to the second type of test though, things get a little trickier;

“Antibody tests check your blood by looking for antibodies, which may tell you if you had a past infection with the virus that causes COVID-19.” states the CDC on their website. The information piece on the government website then continues to describe the meaning of testing positive for the antibody test:

“A positive test result shows you may have antibodies from an infection with the virus that causes COVID-19. However, there is a chance a positive result means that you have antibodies from an infection with a virus from the same family of viruses (called coronaviruses), such as the one that causes the common cold.”

While it is also noted that “except in instances in which viral testing is delayed, antibody tests should not be used to diagnose a current COVID-19 infection”, antibody test numbers are still being reported in several states (Pennsylvania, Texas, Georgia, Vermont and Virginia) according to the American newspaperthe Atlantic.

Since antibody testing is still in a research phase and taking into account the fact that it also might detect past infections (which could be caused by other types of corona viruses as well) the logical conclusion would be to deem antibody testing highly inaccurate. This idea was also entertained by Elizabeth Cohen, CNN’s senior medical correspondent: “If you put the two tests together, you fool yourself into thinking you’ve done more testing than you have.” She pointed out in an article published in late May on the news outlet’s website.

Apparently, this is not how the US government and the CDC think;

According to an article published in the American newspaper The Hillback in May, the CDC acknowledged that they are combining the result from viral and antibody COVID-19 tests when reporting the country’s testing totals, despite marked differences between the tests.

To summarize what this means in a nutshell, a great analogy was given by Ashish Jha, professor of Global Health at Harvard and the director of the Harvard Global Health Institute, in an interview in the Atlantic: “The viral testing is to understand how many people are getting infected, while antibody testing is like looking in the rearview mirror. The two tests are totally different signals” Conflating the results of the two tests could lead to the skewing of the overall positivity rate, a measurement that is one of the benchmarks used in the reopening guidelines.




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