Doctors and public health experts are concerned that Saturday may be too soon for President Trump to resume activities, both for his own health and the safety of those around him.

"Reckless," Dr. Eric Topol of the Scripps Research Translational Institute said in an email after Trump's physician said the president could resume "public engagements" as soon as Saturday.

Trump has said he wants to do events as early as Saturday, but the White House has not released information about what his schedule will entail. His doctors last updated the public on his condition late Thursday, and it was not clear when the next update would be provided.

"We need the timeline of when he got infected ... to prove he isn't infectious," Topol wrote.

COVID-19 patients are supposed to remain in isolation for at least 10 days after their symptoms began to ensure they aren't still contagious and don't spread the virus to other people, according to guidelines from the Centers for Disease Control and Prevention.

"If his symptoms started Wednesday, that would imply that he was maximally infectious around the time of the debate," Dr. Rochelle Walensky, chief of infectious diseases at Massachusetts General Hospital in Boston, said in an interview with NPR.

In that case, Saturday would be in line with the CDC's 10-day recommendation. But that scenario would also raise questions about the president's presence at the debate. If his symptoms began later, Saturday would be too soon, Walensky and others said.

"He is around other very important people. He should not put anyone in harm's way," Dr. Michael Mina, an infectious disease specialist at the Harvard T.H. Chan School of Public Health, wrote in an email.

"We know he fails to use a mask and continues to act irresponsibly in that manner," Mina wrote. "They should be working as diligently as possible to ensure that the president does not pose a clear and present danger to any other people."

Moreover, the CDC recommends people with more serious cases of the diseaseremain in isolation even longer — for up to 20 days. It's unclear how to characterize the president's case since so little information has been released. His doctors have given conflicting information, sometime suggesting it was a mild case. At the same time, he received treatment typically used in severe cases.

"I think it's not likely the case that the president had a severe bout, but again, more transparency would make that an easier determination to make," said Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security.

The steroid the president was prescribed could also potentially extend how long he may be infectious by suppressing his immune system's response to the virus, several experts said.

"The game changer here is the steroids," Dr. Ashish Jha, dean of the Brown School of Public Health, said in an interview. "There is now pretty good evidence it can lengthen viral shedding in COVID-19."

Allowing the president to resume activities prematurely "certainly is consistent with the idea of at every turn doing less than is appropriate," said Marc Lipsitch, a professor of epidemiology at the Harvard T.H. Chan School of Public Health.

It's not known whether Trump's medical team has performed the kind of sophisticated testing that would detect living virus in his body, because information has been limited. That testing would be the only way to know for sure that Trump isn't contagious.

"If they find virus protein or they find culturable virus, then he would be likely to still be at risk of transmitting virus," Mina said. "If they find no viable virus and no protein, then it would be reasonable to assume that he is no longer infectious."

Beyond the implications for people around him, it was inadvisable for the president to resume activities for his own health, several doctors said.

"This is a 74-year-old gentleman who just had hospitalizing disease — perhaps a hospitalizing viral pneumonia," Walensky said. "Being out and about on the campaign trail may, in fact, not be the best thing for him. People generally take a little bit more time than that to convalesce."

Steroids tend to mask symptoms, making people feel like they're better than they really are, she noted.

Several experts said the scant information released about the president provides little insight into his current condition. A single measurement of his respiratory rate is meaningless, for example, they said. What would be more important is his blood oxygen level and respiratory rate after he exercises, they said.

"I would be interested in the oxygen saturation when he walksbecause it provides information about respiratory reserve," said Dr. Rajesh Gandhi, another infectious disease expert at Massachusetts General Hospital.

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