It has been claimed on social media that the Centers for Disease Control and Prevention (CDC) in America has stopped using RT-PCR tests as they cannot differentiate between Covid-19 and the flu. This is not true.
These claims appear to originate from a news site called TrialNews, which published an article with the headline: “CDC Drops the RT-PCR Test as It Doesn’t Differentiate COVID-19 & Influenzas”.
Reverse transcription PCR (RT-PCR) tests are the name given to PCR tests that use the enzyme reverse transcriptase. This is particularly useful when testing for RNA viruses, such as SARS-CoV-2. There are now many different RT-PCR tests in use.
The main text of the TrialNews article specifies that the CDC has withdrawn its request to the U.S. Food and Drug Administration (FDA) for emergency use authorisation for one particular type of PCR test called the ‘CDC 2019-Novel Coronavirus (2019-nCoV) Real-Time RT-PCR Diagnostic Panel’. However this is not clear from the headline, which has been shared in isolation on Facebook.
The article also says: “After December 31, 2021, the CDC will withdraw the emergency use authorization of the PCR test for COVID-19 testing. The CDC finally admitted the test does not differentiate between the flu and COVID virus [sic]”.
This isn’t true. Firstly, the CDC is withdrawing its request to the FDA for the emergency use authorisation for this particular PCR test, it is not itself withdrawing the authorisation. An emergency use authorisation allows the FDA to authorise the use of unapproved medical products or new uses of approved medical products required in an emergency (like the pandemic) in America, when certain criteria are met.
More importantly, however, the CDC 2019-Novel Coronavirus (2019-nCoV) Real-Time RT-PCR Diagnostic Panel was introduced early in the pandemic and can only detect SARS-CoV-2. It cannot test for other viruses such as influenza simultaneously but this doesn’t mean it will confuse the two—it can ‘differentiate’ between them.
We have written about similar claims before. The Department of Health and Social Care previously told Full Fact that it does not use the CDC test in question.
The CDC previously told Full Fact that the CDC 2019-Novel Coronavirus (2019-nCoV) Real-Time RT-PCR Diagnostic Panel is “a highly accurate test” and the decision to discontinue the request for emergency use authorisation was not due to worries about the test’s performance. Instead, the spokesperson explained that since this type of test was introduced, more PCR tests have become available which are “faster, have higher throughput [quicker processing] and are designed to be more efficient”.
The CDC also said that it is encouraging public health labs to adopt a different type of PCR test (the CDC Influenza SARS-CoV-2 (Flu SC2) Multiplex assay) which allows simultaneous testing for both influenza and SARS-Cov-2. This means that rather than individuals having to be tested for Covid-19 and then other respiratory viruses, this test involves taking one sample which can then be simultaneously tested for influenza and SARS-CoV-2.
Covid-19 PCR tests are very accurate tests, and are specific for the SARS-CoV-2 virus because they detect the presence of its genetic material. Like all tests they will have a small number of false positives and false negatives, but they will not accidentally misinterpret the presence of other viruses such as influenza for SARS-CoV-2. We have written about this before.
There are many other PCR tests which have been, and continue to be, authorised for use by the FDA for Covid-19 testing.
Image courtesy of New Jersey National Guard, via Flickr.