The Common Cold And Rumors Of False-Positive CoV-2 Tests

Rapidly spreading rumors on social media are claiming that the recent increase in coronavirus cases in many states is the result of false positive tests due to the common cold coronavirus.  

This is NOT accurate.

This rumor fails to distinguish between antibody testing vs testing for the virus itself. Both tests are being done and they are not carefully reported and distinguised in the press. Antibody tests are being done by epidemiologists who want to know how far and wide the virus has spread and to know how many people exposed to it do not get sick. The antibody test does not determine whether someone is infected.

“Antibody tests” looks for antibodies to a coronavirus in a drop of blood from a finger stick, and they simply determine whether or not you have been exposed to a coronavirus. They do not say that you are currently infected with it. And a positive antibody test could be due to the CoV-2 virus that causes COVID-19, or it could be due to a coronavirus that causes about 30% of cases of the common cold. This test is NOT used to diagnose a current CoV-2 infection, it is just used to measure how many people have been exposed to the virus. Viral antibodies can linger for a few weeks after you clear the infection.

Positive antibody tests are not what health agencies are talking about when they say cases of COVID-19 are increasing, or when they say the incidence of infection is increasing.

When health experts say “cases are increasing,” they refer to cases of diagnosed COVID-19 illness. When they say that the incidence of infection is increasing, they mean that the number of people actively infected with CoV-2 is increasing. These are the numbers we should pay attention to when talking about the spread of the pandemic, not the antibody tests.

In contrast to antibody testing which just shows whether or not you have been exposed, health care folks detect active CoV-2 infections by taking a nasal swab that picks up virus budding from cells in your upper respiratory tract. They then use a highly specific and highly sensitive molecular test called RT-PCR, that your humble correspondent helped develop, to detect the presence of the viral genome.

This molecular diagnostic test, along with a clinical diagnosis of COVID-19 disease, are what people generally refer to when they say that the coronavirus is spreading.

Admittedly, the press too often does not distinguish whether they are talking about increasing antibody tests vs increasing clinical and molecular diagnoses. This contributes to some of the confusion leading people to leap to the unwarranted conclusion that it is a common cold, rather than CoV-2, that is spreading.

But, they are still wrong.

Comments

[Earl]

What is the precise definition of "clear the infection," and how is that determined or measured?

[Steve]

Most often, once symptoms of the illness have passed, it is assumed that the virus has been cleared from the body. This is sometimes confirmed by testing for the virus using the nasal swab and RT-PCR detection of the viral genome. If it comes up negative, it is evidence that the infection has been cleared from the body.

[Earl]

Thank you for that. I understand that the RT-PCR test is sensitive enough to detect non-replication competent viral debris after the immune system has won the battle. Also, I've read that symptoms can persist for weeks after, the body has (you guessed it) "cleared the infection." How then is it determined that the body has "cleared the infection"? Is this a case of imprecise reporting (i.e., misuse of a medical term) by the popular media? Thanks for your clear writing on this important subject that we are all struggling to understand. (Earl)

[Steve]

Doctors definitively determine that the infection has cleared the body when a repeat RT-PCR test comes up negative for the virus. And there are reports of people who test negative for the virus, but who continue to have symptoms many weeks later. There seem to be different reasons that their symptoms continue as I blogged about here:
https://stevensclark.typepad.com/coronavirus_news_and_view/2020/07/some-young-covid-19-patients-are-not-getting-better.html

Also, yes, there is some media miss-reporting, or inaccurately using medical science terms to describe what is going on. I also have posted a couple of blogs about that too.

I am glad you seem to find the blog interesting. Feel free to share it with your friends and ask any questions.