A Covid-19 diagnostic test won’t get other coronaviruses

A post on Facebook makes a number of claims about the Covid-19 pandemic, centring on the assertion that Covid-19 tests do not test for Covid-19 specifically, but any coronavirus, including ones which cause “nothing more than cold/flu like symptoms”. (Some coronaviruses cause what we know of as the common cold.) 

This is false. 

As we have written about extensively here, the diagnostic test used in the UK is called a PCR (polymerase chain reaction) test, which looks for the virus’s genetic material to see if someone currently has Covid-19. 

The Facebook post questions the reliability of PCR tests and there is something in this. 

PCR tests can sometimes indicate that someone does not have the virus when they do (false negative). They can also indicate that someone has the virus when they don’t (false positive).

It’s hard to say how many false negatives and positives PCR tests produce, but in general, these tests are “highly accurate”. 

Most importantly, what a PCR test won’t do is misinterpret the presence of other coronaviruses as the presence of the virus which causes Covid-19, as this post claims.

The possibility that a test might pick up related viruses that have genetic similarities to the virus you’re looking for (technically known as “cross-reactivity”) is something that is looked at when designing PCR tests. 

For example, one of the earliest PCR testing protocols, which was published on 13 January, specifically checked that the test did not pick up the four human coronaviruses that cause infections including the common cold. 

Results for a range of available PCR tests show that they do not cross-react with any viruses analysed, including other coronaviruses.

Where some of the confusion might have come about is because of the accuracy of antibody tests. The US Centers for Disease Control and Prevention says: “There is a chance that a positive result means you have antibodies from an infection with a different virus from the same family of viruses.”

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