WASHINGTON -- Democratic nominee Joe Biden made an abbreviated campaign visit to Grand Rapids, Michigan, on Friday, hours after he tested negative for the coronavirus in two separate tests.
"I'd like to start by acknowledging [and] sending my prayers for the health and safety of the first lady and president of the United States," said Biden at an event hosted by the United Food and Commercial Workers International Union. "My wife Jill and I pray that they'll make a quick and full recovery."
"This is not a matter of politics," Biden continued. "It's a bracing reminder to all of us that we have to take this virus seriously."
President Donald Trump and the first lady tested both positive for coronavirus infection late Thursday, as did top White House aide Hope Hicks. On Friday, Trump was transferred to Walter Reed Army Medical Center.
Shortly after Biden's speech, a top campaign adviser, Ron Klain, confirmed that the Biden campaign will halt its negative advertising against the president for the time being.
Biden told the assembled guests in Grand Rapids that he was late to the speech (originally scheduled for 1:30 p.m.) because he was awaiting the results of two separate coronavirus tests.
"We wanted to make sure that we're doing everything by the numbers, so I got two, two COVID tests this morning. One in Delaware and one by the former White House doc who came up. And everything is clear, we wanted to make sure everything was clear before I came," Biden said at the start of his remarks.
Biden also tweeted about the negative result earlier in the day.
The Biden campaign said the former vice president and his wife, Jill Biden, were both tested Friday morning out of an abundance of caution.
One negative test after potential exposure to the virus is not enough, however, to guarantee that a person hasn't contracted Covid-19, said Michael Osterholm, an epidemiologist at the University of Minnesota.
"All the people who said they were at the debate or at the rally here in Minnesota, or at a fundraiser here in Minnesota this week, none of those tests really are that meaningful to me yet by saying they're negative," Osterholm said on CNBC's "Power Lunch."
Once a person is exposed, he added, it could be up to 14 days before they exhibit signs or symptoms of infection. "Most of the people will be showing signs of illness if they're going to get ill and be positive by testing at seven or eight days."
During the presidential debate Tuesday in Cleveland, Biden was in the same room as Trump was for nearly two hours on stage.
Neither man wore a mask on stage, nor did debate moderator Chris Wallace. But Trump and Biden's podiums were placed approximately 8 feet apart, and they didn't get close to one another. The Centers for Disease Control's current guidance for social distancing is 6 feet.
Biden's running mate, Sen. Kamala Harris left Washington at midday bound for Las Vegas, where she was scheduled to hold an event Friday evening.
Harris was tested for Covid-19 on Thursday, and she tested negative, campaign aides said. She also tested negative Friday.
Democratic National Committee Chair Tom Perez, who attended the debate with Biden, also tested negative on Friday, a spokeswoman said.
Both Biden and Harris sent best wishes to the president and first lady on Friday.
Former President Barack Obama also sent the Trump's best wishes. "Let me start by just stating that although were in the midst of a big political fight and we take that very seriously, we also want to extend our best wishes to the president of the United States and the first lady," Obama said at the start of a virtual fundraiser.
Earlier in the day, Biden campaign manager Jen O'Malley Dillon sent an email to staff assuring them that the campaign was taking every health precaution to protect Biden, Harris and their families. She also asked them not to post on social media about Trump's diagnosis without prior approval.
The email, which was obtained by NBC News, underscores the political sensitivity of the president's diagnosis in the context of the presidential race.
During Tuesday's debate, Trump mocked Biden for wearing a mask, which the CDC recommends as a key element of preventing infection.
"I don't wear face masks like him," Trump said of Biden. "Every time you see him he's got a mask. He could be speaking 200 feet away ... and he shows up with the biggest mask I've ever seen."
Trump also mocked Biden for not holding large rallies the way Trump has been doing since late August.
Many, if not most, of the people at Trump's rallies are squeezed closely together and not wearing masks. Several of them have been held in defiance of state and municipal orders that prohibit large gatherings.
Biden, meanwhile, has strictly enforced social distancing, masks and crowd limits at his events. As a result, his campaign events have featured chairs spaced far apart and typically just a few dozen people.
-- CNBC's Kevin Stankiewicz contributed reporting.