President Donald Trump's revelation on Friday that he and first lady Melania Trump have tested positive for COVID-19 has raised the question of Joe Biden's potential exposure to the illness at Tuesday's presidential debate.
The Democratic presidential nominee did not shake hands with Trump and appeared to be properly socially distanced from him onstage at the debate in Cleveland, following the guidelines from the Centers for Disease Control and Prevention, but NBC News medical contributor Dr. Vin Gupta said on TODAY Friday that those precautions may not have been enough to protect Biden.
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"I think this is a deep concern," Gupta told Hoda Kotb and Savannah Guthrie. "What we know now with COVID-19, what we didn't know a few months ago, is that frankly 6 feet may not be enough, especially in an indoor environment that is not well ventilated.
"You can't really ventilate any indoor environment very well, and there was air conditioning, there was some degree of air flow happening, so no one is protected and everybody has to assume that they need to quarantine, that they need to quarantine for the full 14 days."
Biden had not shared any test results for the illness as of early Friday, but did tweet his wishes to the Trumps for a swift recovery.
Health experts have stressed that close contact indoors without masks and proper ventilation is one of the primary ways that coronavirus spreads.
"The probability of infection increases with the time that particles remain in the room," Rainald Lohner, who runs the Center for Computational Fluid Dynamics at George Mason University, told NBC's Vicky Nguyen on TODAY Tuesday. "And it also increases with the number of particles that you inhale. Ventilation is very important."
While Trump tweeted Friday that he is in isolation at home, the potential exposure could also mean Biden curtailing his campaign to isolate with 31 days to go until the presidential election. Trump, 74, and Biden, 77, are also in a higher-risk group of serious complications because of their age, according to the CDC.
The next presidential debate is scheduled for Oct. 15 in Miami.
"And a negative test does not exonerate them to go back on to the campaign trail, whether it's the Biden campaign or the Trump campaign," Gupta said. "This is a very, very serious event. Six feet really is effectively nothing given the nature of this virus and the more we learn about it."
Before sharing that he and the first lady had tested positive, Trump tweeted that one of his closest senior advisers, Hope Hicks, had tested positive and that the Trumps were awaiting their own results. Trump later tweeted that he and his wife had both tested positive and would "begin our quarantine and recovery process immediately."
"I'm worried," Gupta said. "The president is 74 and he also has something called metabolic syndrome. His weight's above a level that we would actually call him overweight/obese. That combination, anecdotally I've cared for several patients with that double whammy of being a higher age and also being overweight.
"If they get sick, if they become symptomatic, they escalate quickly potentially to needing or requiring ICU-level care, so you can imagine his physicians will be looking at his oxygen level using something called a pulse oximeter, they'll be seeing if he's short of breath, does he have a fever, does he have chills or a cough. Extreme vigilance here is warranted for the president, for the first lady, for anybody, but they're going to be looking specifically at those early signs and symptoms that might suggest that he needs hospital-level care."
The health of Hicks, 31, is also a concern along with everyone she came in contact with while traveling with the president in the days before her positive test.
"And critically what is Hope Hicks feeling like?" Gupta said. "Because if she was a high-risk exposure because she's very symptomatic at a young age, then that's concerning. That means everybody on Air Force One, everybody else they potentially came in contact with, needs to isolate for 14 days by CDC guidelines."
The press secretary for Vice President Mike Pence announced Friday that he and wife Karen Pence have both tested negative for the virus, but it's unclear whether they will enter isolation.