A close friend – let’s call him John – recently called, asking for advice. He woke up with severe muscle aches and fatigue. Understandably worried that it could be COVID-19, he asked whether he should go to work, run to get a test or stay home. Because he didn’t have other symptoms, such as a fever, cough or shortness of breath, he was unsure what to do. Of course, this could be any other respiratory infection, such as the flu or the common cold, but what if it is COVID-19? What is the risk of him transmitting the virus to others?
To understand when people with COVID-19 are most likely to be infectious, our team conducted a study which was recently published in The Lancet Microbe.
We investigated three things: viral load (how the amount of the virus in the body changes throughout infection), viral shedding (the length of time someone sheds viral genetic material, which does not necessarily mean a person is infectious), and isolation of the live virus (a better indicator of a person’s infectiousness, as the live virus is isolated and tested to see if it can replicate in the laboratory).
We also found that genetic material can still be detected in throat swab or stool samples for several weeks. But no live virus was found in any sample collected beyond nine days of symptoms. Although some people, especially those with severe illness or with a weakened immune system (say from chemotherapy), may have longer viral shedding, the results suggest that those infected with SARS-CoV-2 are most likely to be highly infectious a few days before symptoms start and the following five days.