Trump must isolate for 10 days from the time his first coronavirus symptoms appeared, experts say

• President Trump has tested positive for the coronavirus and gone into isolation with the First Lady.
• On Friday, he was transferred to Walter Reed Medical Center.
• Infectious-disease experts and the CDC recommend that people with COVID-19 isolate for 10 days after they first show symptoms.
• That's shorter than the 14-day quarantine period because people with symptoms are unlikely to be infectious after 10 days.

President Donald Trump and the First Lady have tested positive for the coronavirus and gone into isolation. Guidelines from the Centers for Disease Control and Prevention say they'll need to remain isolated for 10 days after their first symptoms appeared.

That's because data shows that COVID-19 patients stop shedding enough virus to infect other people by the 10th day of their illness — that is, as long as they've had no fever for at least 24 hours without using fever-reducing medication. Studies have found very few cases in which symptomatic people were infectious after 10 days.

"A lot of data were showing that once you develop symptoms, you only have infectious virus — virus that's capable of infecting other individuals — for 7.7 days after developing symptoms," Monica Gandhi, an infectious-disease expert and professor of medicine at the University of California, San Francisco, told Business Insider. "So it's quite exact."

There are, of course, exceptions. In some cases, people with severe illness and those who are immunocompromised have continued to shed infectious levels of virus after 10 days. In such cases, the CDC recommends extending isolation to 20 days.

The guidelines about isolating after a diagnosis differ from quarantine recommendations. The latter, intended for people who have been exposed but not yet tested positive, is determined based on the virus' known incubation period. Two weeks is enough time for the virus to grow to detectable levels inside the body.

"The maximum amount of time from being exposed to someone who has it to developing symptoms is 14 days," Gandhi said. "That quarantine timeframe has not changed."

Even negative test results don't get you out of a 14-day quarantine, she added.

Isolation for no less than 10 days after symptoms appear

Trump was experiencing a low-grade fever, cough, nasal congestion, and fatigue on Friday, The New York Times reported. He received an injection of Regeneron's experimental antibody drug, after which he walked to a helicopter on the White House lawn to be transported to Walter Reed Medical Center. The White House has said Trump will stay there for a few days.

It is unclear when the president's symptoms began, but pinpointing their start is essential in determining when he can leave isolation. If Trump began to feel unwell around the time he tested positive on Friday, for example, he would need to isolate until October 12.

Reporting from Bloomberg suggests that Trump's aides first noticed his fatigue on Wednesday. If that was his first symptom, it would mean Trump should remain isolated until October 10.

Regardless, Trump should not come out of isolation before that 10-day period has passed, since he could infect others until then, according to Amesh Adalja, a senior scholar at the Johns Hopkins University Center for Health Security. That will remain true even if he tests negative in a few days.

"We don't test people to say they're non-infectious," Adalja told Business Insider. "We wait 10 days and say: Are they better? Have their symptoms decreased? Are they not having a fever for the last three days and not taking Tylenol or ibuprofen? And then we release them."

No medication could cut that 10-day period short, either.

"There's no prophylactic therapy. There is no treatment for mild disease," Gandhi said. "So there's really nothing to be done but just wait it out."