President Trump held a rally less than two weeks after testing positive for COVID-19. Joe Raedle/Getty Images
  • We don’t have a test to determine how much a person may transmit the coronavirus, so doctors have to judge this based on their symptoms.
  • President Trump and Senator Mike Lee made headlines for appearing in public after developing COVID-19.
  • COVID-19 is still a new disease that scientists are working to understand. 

On Monday, President Trump held his first in-person rally since testing positive for COVID-19 ten days ago. 

Meanwhile, Senator Mike Lee, who also recently developed COVID-19, spoke without a mask for several minutes at Supreme Court nominee Amy Coney Barrett’s nominating hearing. 

Both of the doctors who treated Trump and Lee’s infections claimed the two were no longer infectious and posed no threat to public health, based on current coronavirus guidelines from the Centers for Disease Control and Prevention (CDC) which state most people are in the clear 10 days after the onset of symptoms. 

But knowing how contagious a person may be isn’t so black and white. 

We don’t have a test to determine how contagious a person might be, so doctors have to judge a person’s level based on their symptoms. 

A polymerase chain reaction (PCR) test, which is used to diagnose COVID-19 by swabbing the throat or nose, can help determine if a person is still carrying the virus but it doesn’t always tell us if they’re still contagious. 

How to tell if you can transmit the virus

Dr. Amesh Adalja, an infectious disease physician and senior scholar for Johns Hopkins University Center for Health Security, says there are two ways to determine when it’s safe for someone recently diagnosed with COVID-19 to be around others again. 

The first and preferred method is to evaluate your symptoms. 

“The simplest way is to wait a period of 10 days from symptom onset in mild to moderate cases (up to 20 days in severe cases) and then you can discontinue that person from self-isolation,” Adalja told Healthline. 

This is in line with the CDC’s guidelines, which state people with COVID-19 can be around others when:

  • it’s been 10 days since their symptoms first appeared
  • they haven’t had a fever in 24 hours (without using a fever reducer)
  • other symptoms — like cough or fatigue — are improving

Those who are immunocompromised or had a severe case of COVID-19 should isolate for at least 20 days after the onset of symptoms. 

“I think it’s important to look at their clinical picture: How are they doing, how are they feeling, what are their symptoms?” Dr. Matthew Heinz, a hospitalist and internist in Tucson, Arizona, said. 

If they’re having fevers, there’s likely some degree of active infection and it’s important to continue self-isolating, Heinz added. 

The second method is to administer a PCR until a patient tests negative for COVID-19 at least two times. 

“We think that a patient with a negative PCR or with a very low positive PCR is probably not infectious,” says Dr. Sheldon Campbell, a pathologist in Yale Medicine’s Department of Laboratory Medicine. 

“A negative PCR is a pretty good sign someone isn’t infectious,” Campbell added. 

But there’s a caveat to using a PCR test to determine a person’s ability to transmit the virus. 

“There are going to be individuals that shed nonviable viral debris (and will test positive) for some period of time but not be contagious,” Adalja said, noting that he prefers the time-based symptoms approach rather than a PCR test.

Though some people may potentially shed small amounts of virus weeks after being diagnosed, others who continue to test positive may be carrying noninfectious viral remains in their body, according to Heinz.

A PCR test is not yet approved by the Food and Drug Administration (FDA) for quantitative reporting, or reporting whether a person has a high or low level test result, according to Campbell.

“We’re not quite at the point of being able to use a PCR test quantitatively,” Campbell said.

We’re still learning a lot about the virus 

Though it may seem like COVID-19 has been around for a while now, the truth is that it’s still a novel disease that scientists are working to understand. 

Heinz says measuring a person’s ability to transmit the virus is not an exact science.

“It’s not the easiest thing to determine,” Heinz said. 

Because there are so many unknowns, Heinz suggests playing it safe if you were recently diagnosed with COVID-19. 

If it’s been 14 days since the onset of symptoms and someone is still testing positive, it’s safe to assume they’re still potentially able to transmit the virus, at least to some degree. 

“I would still say don’t risk it. At a minimum, [the CDC is] saying 10 days, but I still say 14 to most of my patients to be extra cautious,” Heinz said.  

In the meantime, everyone, including those who have recently recovered, should continue to physically distance from others and wear masks, as they’re our best bet at blocking community transmission. 

The bottom line 

Though current CDC guidelines suggest most people with a COVID-19 diagnosis will no longer pass the virus to others 10 days after the onset of symptoms, health experts say measuring this may be tricky.

Some people will continue to test positive for COVID-19, and while this could indicate they’re still able to transmit the virus, others who test positive may just have nonviable viral remains in their throat and nose.

Until we have more data, health experts recommend playing it safe for at least 10 to 14 days after diagnosis. 

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