The coronavirus can linger in the air in tiny particles. The president spends a lot of time indoors with others and disdains precautions.
On Saturday, President Trump met with Judge Amy Coney Barrett, the nominee to the Supreme Court, and others in the Oval Office. On Tuesday, he debated former Vice President Joseph R. Biden Jr. in an indoor hall, neither with a mask, talking at high volume and often without pause. On Wednesday, Mr. Trump traveled to and from Minnesota on Air Force One along with dozens of others. On Thursday, the president appeared indoors before hundreds of supporters at a golf club in Bedminster, N.J. On none of these occasions was the president wearing a mask. Often, neither were many in the room or on the airplane with him. All in all, conditions like these are a recipe for so-called super-spreader events, in which a single infected person transmits the virus to dozens of others, research has shown. “The White House has been flouting the basic rules of public health for a very long time,” said Dr. Ashish K. Jha, dean of the School of Public Health at Brown University in Providence, R.I. Regarding the president’s diagnosis that he was infected with the coronavirus, he added, “there are no surprises here.” The problem is one scientists have been warning about for months: airborne transmission. In addition to the heavy droplets sneezed or coughed out by infected people, research has shown the coronavirus may drift in the air indoors, held aloft in tiny particles called aerosols. Now the White House is trying to pin down exactly who had contact with Mr. Trump in recent days — and to whom these people in turn may have passed the virus. Potential contacts may number in the hundreds. All of those people will have to be identified, tested and quarantined. “Rather than looking for a needle in a haystack, it’s like Trump is the needle and you’re trying to find out if it touched each piece of hay,” said Angela Rasmussen, a virologist at Columbia University in New York. Experts may never know how the president was infected or whom he may have infected. The Rev. John I. Jenkins, president of the University of Notre Dame, tested positive for the coronavirus after attending a White House ceremony on Saturday for Judge Barrett. So did Senator Mike Lee, Republican of Utah. The timing raises the possibility that the president could have been infected over the weekend, scientists said. Most people develop symptoms about five days after being infected with the virus, so exposure over the weekend would fit with reports that the president was showing early symptoms on Wednesday and Thursday. People are thought to be most contagious to others a day or two before the onset of symptoms. “We know that presymptomatic transmission drives a significant amount of spread of this virus,” Dr.
