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Is the president still contagious? Probably not, experts say

The evaluation of the president raised some questions, but the findings do follow guidance from the CDC and the World Health Organization.
President Donald Trump takes his mask off before speaking from the South Portico of the White House during a rally Saturday.Mandel Ngan / AFP - Getty Images

Less than two weeks after President Donald Trump announced that he tested positive for Covid-19, he is back on the campaign trail, appearing maskless while boarding Air Force One and before crowds at a Florida rally.

That has caused some alarm, but doctors say that what we know about the coronavirus and the president's medical tests mean he's probably not contagious anymore.

Trump’s doctors announced Monday that the president is “not infectious to others” after undergoing a series of tests that are used to determine if a patient is at risk of transmitting the coronavirus. Though Dr. Sean Conley, the president’s physician, has repeatedly sowed doubt and confusion by dodging questions and withholding details of the president’s diagnosis and treatment, experts say Conley’s assessment lines up with what’s known about the Covid-19 recovery process.

In a memo released Monday, Conley said the president tested negative on rapid antigen tests on consecutive days. These tests, which are designed to detect viral proteins that trigger an immune response in the body, can help determine the presence of a current viral infection. Conley added that other clinical and laboratory data were used to determine that Trump is no longer at risk of spreading the virus to others.

“This comprehensive data, in concert with the [Centers for Disease Control and Prevention’s] guidelines for removal of transmission-based precautions, have informed our medical team’s assessment that the President is not infectious to others,” Conley wrote in the memo.

Infectious disease experts say that Conley’s evaluation raises some questions, but the findings do follow guidance from the CDC and the World Health Organization.

The CDC states that Covid-19 patients can be around other people again 10 days after the onset of symptoms, provided that the person has not had a fever for the past 24 hours without using fever-reducing medications and if other symptoms are also improving.

“There’s good data now that if someone is not that sick and has resolution of their fever and you follow these individuals over time, by about the 10 day mark, it’s exceedingly unlikely for them to be contagious to other people,” said Dr. Isaac Bogoch, an infectious diseases physician and associate professor of medicine at the University of Toronto.

Studies have shown that people are likely most at risk of transmitting the virus one or two days before experiencing symptoms, with the period of contagiousness extending for about a week after that.

For more severe cases, the CDC recommends lengthening the period of isolation for up to 20 days. And there are other caveats, according to Dr. Helen Boucher, chief of the infectious diseases division at the Tufts Medical Center in Boston.

“With people who are severely immunocompromised — so maybe people who have received organ transplants — it could last longer,” she said.

Dr. Daniel Kuritzkes, head of the division of infectious diseases at the Brigham and Women's Hospital in Boston, said the CDC provides good guidance for assessing contagiousness, and added that the 10-day isolation period should be adequate for most people with mild cases of Covid-19.

In most cases, testing is not the most useful gauge of a person’s transmission risk because some, including polymerase chain reaction (PCR) tests, can detect fragments of the coronavirus long after a person is contagious, he said.

“We know there are people who can continue to test positive for the virus for quite some time, especially using the PCR tests,” Kuritzkes said. “There’s clearly a distinction between shedding virus and being infectious and contagious to others.”

This means that even people who have symptoms that linger for weeks or even months are not thought to be contagious that entire time.

“PCR tests are so sensitive and so good that you can detect dead, remnant virus,” said Dr. Jeanne Marrazzo, a professor of medicine and director of the division of infectious diseases at the University of Alabama, Birmingham. “If you’re still coughing weeks out, you’re probably coughing up dead virus. It’s way beyond the time when you’re infectious.”

In Conley’s memo, he stated “PCR threshold cycle measurements,” coupled with other lab data, indicated a lack of detectable viral replication. PCR tests amplify genetic material from the coronavirus in cycles, according to Marrazzo, which means the number of cycles usually corresponds to a patient’s viral load, or how much virus is actually in the body.

“When there’s not much virus, you sometimes have to continue to run attempts,” she said. “It’s a really good direct reflection of the amount of virus there.”

Conley’s statement also referred to tests of “subgenomic RNA,” which Marrazzo said can detect fragments of messenger RNA that translate to viral proteins. “What it means when you find those things is that essentially you have genetic evidence of actively replicating virus," she said.

But Boucher said subgenomic RNA tests are experimental, and not part of the regular arsenal available to physicians and patients.

“It’s totally experimental,” she said. “It’s not like we do that test normally in the hospital.”

Bogoch added that it’s difficult to know what value such tests have without more information.

“It’s science by press release — we don’t really know what’s going on under the hood,” he said. “I can’t tell you with any degree of confidence what that test means in a meaningful clinical situation. It’s hard to extrapolate and make guesses based on that.”

But he added that Conley’s assessment generally adheres to what’s known about how most Covid-19 cases evolve, which means the president and others who may have become infected at what has become a superspreader event at the White House on Sept. 26 are likely no longer contagious.

“With clinical medicine, there’s a lot of nuance involved," Bogoch said, "but we know that if it’s been 10 days and the person doesn’t have a fever, the probability that that person is contagious is very low.”