The White House did not say that Trump actually tested negative for the virus – but according to CDC guidelines, people generally don’t need to test negative to be around people again.
Earlier in the pandemic, health officials said people would have to get two negative tests for the coronavirus – taken 24 hours apart – before they end up again. This forced some people to self-isolate for weeks.
But coronavirus tests can’t necessarily determine if someone is infectious. PCR tests, for example, simply look for pieces of genetic material called RNA – and which can linger long after someone has recovered.
According to the CDC, research has shown that people are unlikely to be contagious 10 to 20 days after symptoms start, regardless of test results.
To understand this, the scientists took samples from coronavirus patients and attempted to infect living cells. Although PCR tests can come back positive, people do not tend to be contagious after this 10 to 20 day window has passed.
Think of it this way: a PCR test looks for the blueprint of the virus – its “genome” – not the virus itself. In fact, the test is simply looking for fragments of this plane.
It’s like a chocolate cake recipe; finding the recipe in someone’s kitchen doesn’t mean you’ll find a cake.
Why wouldn’t Trump need to self-isolate for 20 days?
People with mild to moderate Covid-19 would remain infectious “no more than 10 days after symptoms start,” according to the CDC, although people with severely weakened immune systems may need to isolate themselves longer.
Before leaving isolation, people’s symptoms should have improved and they should be 24 hours fever-free, according to the CDC (being still on fever-reducing medication doesn’t count).
For patients with severe Covid-19, the CDC says up to 20 days of isolation “may be warranted”. But the agency’s recommendations only take 10 days. “Consider consulting with infection control experts,” the CDC recommendations say.
The president’s doctor, Dr Sean Conley, released a memo on Saturday referring to Trump’s “advanced diagnostic tests” and stating “there is no longer any evidence of active replication of the virus”.
Yet the letter did not fully describe these advanced diagnostic tests or their exact results.
The president’s doctor said Trump had an undetectable “subgenomic mRNA”. These are molecules produced when viruses replicate. Their absence may suggest that Trump is no longer spreading a live virus.
But Conley did not specify what “advanced diagnostic tests” the president had received. For example, he did not say whether the so-called viral cultivation was carried out. This is the process by which scientists try to infect living cells to see if an active virus is present.
Conley also did not reveal other vital signs of the president, such as his current oxygen levels, leaving many questions about Trump’s current state unanswered.