After hosting a gathering with guests later found to be infected with the coronavirus, President Trump refrained from getting tested, let alone from self-quarantine, even as administration officials urged Americans to adopt stern new precautions.
Mr. Trump finally underwent testing for the virus on Saturday morning and was reported to be negative on Saturday evening. Still, the episode has startled and disconcerted medical experts, who worry that it sets a poor example for Americans and suggests that the president still does not fully understand the risks the country faces.
Indeed, Mr. Trump should be tested regularly even without symptoms, given his frequent appearances at campaign rallies and his interactions with top leaders who are instrumental in running the country, said Arthur Caplan, a bioethicist at N.Y.U. Langone in New York. The test results should be made public, he said.
“It is the height of irresponsible leadership to continue to risk catching or spreading Covid-19 or other infectious diseases,” said Dr. Caplan, referring to the illness caused by the coronavirus.
Last weekend at Mar-a-Lago, the president’s estate in Palm Beach, Fla., Mr. Trump hosted both a dinner and a birthday party that was attended by President Jair Bolsonaro of Brazil, whose entourage included his chief communications officer, Fabio Wajngarten.
The president stood shoulder to shoulder with Mr. Wajngarten, who leaned toward Mr. Trump for a photo. A few days later, Mr. Wajngarten, who developed flulike symptoms once home in Brazil, tested positive for the coronavirus.
Two other people who attended gatherings with the Brazilian officials on the trip have since learned they are infected: Mayor Francis Suarez of Miami, who was tested even though he has no symptoms; and Brazil’s chargé d’affaires in Washington, Ambassador Nestor Forster Jr., who discovered he was infected on Friday evening.
The ambassador had already self-quarantined, after learning of Mr. Wajngarten’s infection, and is now extending the measure for two more weeks.
Other politicians who met with members of the Brazilian delegation — including Senator Rick Scott, Republican of Florida, and Senator Lindsey Graham, Republican of South Carolina — quarantined themselves.
But Mr. Trump did not alter his routine.
On Thursday, he met with the prime minister of Ireland, Leo Varadkar. At a news conference on Friday, he stood before a clutch of infection-control experts and business leaders in the White House Rose Garden.
The president shook hands with almost all of the business executives as he invited each to a shared microphone. Neither the handshakes nor the mic seemed particularly sanitary. One medical company executive was prepared — and offered his elbow even before Mr. Trump extended his hand.
The president responded with an elbow bump, saying, “I like that, that’s good.” Mr. Trump said Saturday that he was trying to break the habit of shaking hands, but that it was deeply ingrained.
“It’s a natural reflex,” he said, adding that he used to be a “non-hand-shaker,” but that “people walk up to me and want to shake my hand.”
People who were exposed to a known coronavirus case should be asked to stay home and to monitor their health for 14 days, and be tested if they develop symptoms, according to the Infectious Diseases Society of America.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and a member of the White House Coronavirus Task Force, went further in a televised interview on Friday.
Any individual who has been exposed to someone infected with the coronavirus should be tested, he said. If testing is not possible, “you should try as best as you can to self-isolate,” Dr. Fauci said.
He declined to say whether Mr. Trump should be tested for the infection, however, adding that was up to the president and his White House physician.
At 73, Mr. Trump risks developing particularly severe illness should he become infected. Officials of the White House Task Force were at pains this week to note that older Americans and those with underlying conditions should be particularly vigilant.
The president has made very little personal health information public. But he is known to take medication to lower cholesterol, and obesity — his reported weight is 243 pounds — is one of the underlying conditions that can increase the risk of severe illness.
Some medical experts are calling on the president to curtail face-to-face meetings with heads of state, business leaders and health officials. Mr. Trump’s news conference appearances on small stages packed with nodding officials, even as large American companies send employees home to work, unnerve some scientists.
“It would make sense for him to do some social distancing,” said Dr. Peter Rabinowitz, a professor of medicine and global health at University of Washington in Seattle. “He could set a good example.”
A lower threshold for testing should apply to the president and vice president, who was also in the photo with Mr. Bolsonaro’s aide, because of their critical roles in leading the country, said Dr. Judith N. Wasserheit, co-director of the University of Washington MetaCenter for Pandemic Preparedness and Global Health Security.
The president has two health obligations, said Lawrence Gostin, a professor of global health law at Georgetown University: “Number one, keep himself and the cabinet safe, and number two, to keep the American people safe.”
“No individual, president or not, has the right to expose others to a dangerous virus,” Mr. Gostin added.
The president’s physician, Dr. Sean P. Conley, said on Friday that Mr. Trump’s exposure was “extremely limited” with one individual later found to be infected. Although the president spent more time “in closer proximity” to a second individual who later tested positive, “all interactions occurred before any symptom onset.”
People who are infected may not show symptoms for days, however; they may transmit the virus to others during this period, studies have shown.
Other administration officials have brushed shoulders with people who subsequently tested positive. Attorney General William P. Barr and the president’s daughter, Ivanka Trump, met last week with Australia’s minister for home affairs, Peter Dutton, who later said he was infected with the coronavirus.
Senator Ted Cruz, Republican of Texas, who decided to self-quarantine after mingling at a conservative political conference where an attendee had tested positive, is “probably doing the right thing, because as a politician, he is in some cases like a physician or anybody else who sees a high number of people every day,” said Kelly Hills, a bioethicist and co-founder of the consulting firm Rogue Bioethics.
Prime Minister Justin Trudeau of Canada secluded himself even before his wife tested positive for the coronavirus on Friday, and a Spanish deputy prime minister also did so.
Ms. Hills added that “if politicians, in general, are still planning on interacting with the public — glad-handing, kissing babies, whatever — then any politician who has possibly had exposure should probably take quarantine steps.”