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MYTH: People testing positive on RNA tests are infectious
FACT: Viral SARS-CoV-2 RNA does not equal infectious virus

By: Joseph Osmundson
Last updated: Updated May 18, 2020

Most of the tests used to identify SARS-CoV-2 don’t look for the actual virus at all. They look instead for little bits of the viral genes, small pieces of RNA that are necessary for viral replication. SARS-CoV-2 encodes its genome in RNA, not DNA like living cells.

Viral RNA is not sufficient for the virus to replicate. Infectious virus is needed for that. For virus to be infectious,  the RNA must be long and packaged, not just in a membrane, but with surface proteins that will help it bind to human cells.

SARS-CoV-2 viral RNA seems to be ubiquitous on, around, and in infected people. Studies have found viral RNA in patients’ stool samples, all through their hospital rooms, on doctors’ shoes, in the air, and on surfaces on cruise ships up to 17 days after people with COVID-19 are gone.

It remains unclear what relationship there is – if any – between the amount of viral RNA detected in a sample and how much infectious virus is present.

The virus might well survive in some of these places for a time, up to two days, but very limited research has actually been done toward answering these questions.

Studies that look at how much infectious virus is found in various places are fairly rare because BSL-3 lab facilities are required to test viral growth. Viral RNA on a surface or in a sample simply does not mean infectious virus is present. In stool – for example – abundant SARS-CoV-2 RNA can be detected, but scientists have shown mixed results on whether this RNA is due to infectious virus or not, and epidemiologists see no evidence for fecal transmission of COVID-19

Viral RNA does not indicate infectious virus. The viral RNA is necessary for infection but – in itself – not sufficient.

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