How did President Trump become infected with the coronavirus?

The common route of transmission for covid-19, the disease caused by the novel coronavirus, is person-to-person. That means people most often get sick through direct or close contact with other infected people, who may release respiratory droplets from their mouths or noses by coughing, sneezing, speaking, shouting or even singing. Scientists and public health experts say there is also mounting evidence that the coronavirus is airborne, transmitted through tiny droplets called aerosols that linger in the air much longer and travel farther than the larger globs that come from coughing or sneezing.

The more closely a person interacts with others and the longer that interaction, the higher the risk of covid-19 spread. In crowded indoor spaces with poor ventilation, for example, covid-19 can spread widely, although it’s far less infectious than measles.

It is not clear how and when President Trump, who is 74 and has attended several events in recent days without wearing a mask, caught the virus. He was in close contact this week with Hope Hicks, a trusted adviser whose own positive test was announced Thursday, one day after she began to feel ill. Hicks traveled with Trump to Ohio on Tuesday for the debate against Democratic presidential nominee Joe Biden, and on Wednesday evening, accompanied the president to a campaign rally in Duluth, Minn. Ronna McDaniel, the chairwoman of the Republican National Committee, who is in regular contact with the president, also tested positive for coronavirus, an RNC spokesman announced Friday. She last saw the president a week ago Friday.

What are the president’s symptoms?

Early Friday, White House chief of staff Mark Meadows told reporters that Trump is experiencing “mild symptoms.” Two people who spent time with Trump on Thursday, when he attended a fundraiser and delivered a speech at his golf club in Bedminster, N.J., told The Washington Post that he appeared tired.

But his condition appeared to worsen through the day to include low-grade fever, a cough and nasal congestion, and by Friday afternoon, the decision was made to move him to Walter Reed National Military Medical Center, according to two administration officials who spoke on the condition of anonymity to discuss the president’s health. Experts said the move most likely reflects his doctors’ desire to keep him under close observation in a location where they can administer oxygen and other therapies quickly if necessary.

Covid-19 may manifest a variety of symptoms between two to 14 days after exposure. These include coughing, fatigue, nausea, diarrhea, chills, fever, difficulty breathing and the loss of the sense of smell or taste.

In severe cases, people with covid-19 may have difficulty breathing, high fever or chest pain. The virus mainly attacks the lungs but can also harm the heart, brain, kidney and other organs. More than 200,000 Americans have died of the disease.

What are the president’s risks of severe disease?

The most important risk factor for a severe outcome — greater even than having other health problems — is age. The CDC tracks mortality rates by decade — for example, ages 65 to 74, or ages 75 to 84 — and says the risk increases with each additional year within those cohorts.

Trump’s risks are greater because of his gender and weight. Although men and women catch the virus at similar rates, men disproportionately die from the disease. As of June, men represented 57 percent of U.S. deaths.

Obesity, in particular, is associated with increased covid-19 complications, according to a review published in August of dozens of studies. People with obesity, when compared with those of healthy weight, were 113 percent more likely to be hospitalized and 48 percent more likely to die of the disease.

Trump’s weight, with a body mass index of 30.5, according to his most recent medical report, would place him at “increased risk of severe illness,” according to the CDC’s coronavirus advisory on risk factors. The agency said a body mass index of 30 or higher has increased risk.

The severity of the president’s illness may also be dictated by whether he inhaled a large amount of virus deep into his lungs. His failure to wear a mask regularly may have left himself vulnerable to receiving a heavy dose of the virus, which is correlated with worse outcomes.

Trump also takes a statin for high cholesterol and has slightly elevated blood pressure. Hypertension is not considered as great a risk factor as obesity by the CDC, which says people with that condition “might” be at higher risk.

How is the president being treated?

Typically, people with mild cases of covid-19 are provided supportive care — such as hydration and acetaminophen for fever and aches and pains after a diagnosis, said Amesh Adalja, an infectious disease expert at Johns Hopkins University Center for Health Security.

But in a memo released Friday afternoon, White House physician Sean Conley said Trump had received a single eight-gram infusion of an experimental drug made by Regeneron Pharmaceuticals. The drug, a combination of two monoclonal antibodies, aims to keep people out of the hospital by generating the body’s own disease-fighting force. Regeneron said the still unapproved experimental therapy was provided to Trump in response to a “compassionate use” request from his physicians. The drug is being tested in a late-stage clinical trial, the company said in a statement.

Conley said the president also is taking zinc, vitamin D, famotidine, melatonin and a daily aspirin. Famotidine is used to reduce the production of stomach acid and melatonin can be employed as a sleep aid.

If Trump were to get much sicker and require hospitalization, doctors would consider additional treatments. In addition to the antiviral drug remdesivir, those could include one or more of the following: supplemental oxygen; the steroid dexamethasone to calm an overactive immune system; and blood thinners to reduce the risk of clots.

Mark McClellan, FDA commissioner during the George W. Bush administration, said the treatments and care for covid-19 have improved sharply in the last six months. “We are seeing much better outcomes in severely ill people,” he said.

How was the president tested for the coronavirus?

Conley, the White House physician, said that Trump’s infection was confirmed by a PCR, or polymerase chain reaction, test, which is considered the most accurate gauge of whether virus is present.

Starting in April, the White House began requiring the president’s visitors to take a rapid-turnaround test, using a machine known as Abbott ID NOW. The machine analyzes nasal swabs, and delivers results in five to 13 minutes, but researchers have found that it can miss infections.

Abbott ID NOW is a viral RNA test, not one of the quick antigen tests that the Trump administration has been deploying in chaotic fashion to nursing homes around the country. Antigen tests look for a protein that exists on the surface of the coronavirus, and they are less accurate than traditional, PCR laboratory tests.

PCR tests are very sensitive and test for the presence of viral RNA in a sample from the nose or throat, but they take more time to deliver results. They amplify this RNA by using cycles of heating and cooling, so that even a tiny amount of initial virus can be detected, said Tara Smith, an epidemiologist at Kent State University.

In August, Ohio Gov. Mike DeWine (R) tested positive after receiving an antigen test as part of a screening before meeting with President Trump in Cleveland. A follow-up PCR test showed a negative result, however.

The president has been tested regularly. Does that mean he didn’t need to wear a mask or socially distance?

In July, White House press secretary Kayleigh McEnany said Trump was being tested for the coronavirus “multiple times a day,” referring to him as “the most tested man in America.”

Trump quickly contradicted that, telling reporters he was taking tests every two to three days, but did not recall ever having had more than one in a single day.

Whatever the frequency, testing is imperfect. Rapid tests have been shown to be inaccurate, and even PCR tests can return false negatives if a poor sample is taken, or if a person is early in the infection and has very little virus in their body. Because it can take several days for the virus to replicate to levels that would be detectable, a negative test on one day means only that the person tested is unlikely to be infectious on that day, not that they do not have covid-19.

They may still develop covid-19 in the 14 days following exposure, which is why public health experts recommend quarantining for that length of time after exposure.

On Friday, many scientists and public health experts said the president’s positive test offered a clear demonstration that avoiding infection depends on taking basic preventive measures — mask-wearing, social distancing and hand-washing.

“If ever there was a need to demonstrate that testing is not a substitute for safety measures …” former CDC Director Tom Frieden said on Twitter. “No one thing will keep us safe from covid-19. We can chip away at risk by wearing a mask, watching distance, washing hands, reducing indoor crowding, testing and tracing strategically.”

John I. Jenkins, president of the University of Notre Dame, expressed regret Monday that he had removed his mask at a White House event Saturday during which the president nominated Amy Coney Barrett to the Supreme Court, after Jenkins received a negative result from a rapid test.

Officials at the event, he said, had indicated it was “safe.”

After the test, Jenkins wrote in a letter to university students and staff, he was “directed to a room with others, all fully masked, until we were notified that we had all tested negative and were told that it was safe to remove our masks … I regret my error of judgment in not wearing a mask during the ceremony and by shaking hands with a number of people in the Rose Garden.”

Jenkins tested positive on Friday, Notre Dame said.

Is the president in quarantine or isolation? What does that mean?

Trump tweeted early Friday that he and the first lady would “quarantine,” but that is not the correct term for what infected people are urged to do to avoid further spread of the virus.

Meadows said Friday the president is in self-isolation, which separates people who are sick with a contagious disease from those who are not. According to the CDC, infected people should remain isolated for at least 10 days and as long as 20, if their cases are severe. Assuming Trump is following that guidance, he is staying in a specific “sick room,” or area of the executive residence, and using a separate bathroom.

A quarantine is when the movements of an exposed person are restricted while they wait to determine whether they contracted an infectious disease. This helps prevent the spread of disease that can occur before people know they are sick or infected.

What is contact tracing? How might that be done in the White House?

The public health technique called contact tracing helps map and contain the spread of the disease. Disease detectives called contact tracers call, text or otherwise notify people who may have been exposed to an infected individual to determine whether there was any close contact. For the coronavirus, close is defined as spending 15 minutes or more within six feet of an infected person.

Contact tracing is underway in the White House, spokesman Judd Deere told Agence France-Presse on Friday. The White House did not immediately respond to a request from The Post to describe who was tracking links to the president’s case, or over what timeline.

If the president’s symptoms appeared on Thursday, the beginning of his infectious period would likely have been around Tuesday, said Emily Gurley, an epidemiologist at Johns Hopkins Bloomberg School of Public Health.

Though the president came in contact with many people over the last few days, tracing close contacts of famous people is comparatively easy, she pointed out. “How many people have had contact with the president of the United States during the past few days and [would] not remember?” Gurley said.

Contact tracing has successfully curbed Ebola and smallpox outbreaks but has been a challenge in the coronavirus pandemic because of the scope of the outbreak.

President Trump shared a stage with Vice President Biden Tuesday night. Is Biden at risk?

Democratic nominee Joe Biden and his wife, Jill, said on Friday they had received negative results for coronavirus, after their doctor said they had been given PCR tests.

“I’m happy to report that Jill and I have tested negative for the coronavirus,” Biden said in a tweet. “Thank you to everyone for your messages of concern. I hope this serves as a reminder: Wear a mask, keep social distance, and wash your hands.”

The candidates did not shake hands, and they stood at podiums that were separated by more than six feet. Although Biden was distanced from Trump onstage, both were unmasked. Infectivity is high a few days before symptoms develop, and it is possible Trump was infectious on Tuesday, though that is not certain.

Proper ventilation in the debate hall may have helped reduce the risk of any possible viral exposure. Masks were required for the audience, though members of Trump’s family who attended were seen refusing to wear them.

The Cleveland Clinic, one of the debate’s sponsors, said the debate setup followed CDC guidelines. But neither the clinic, nor Case Western Reserve University, the other sponsor, answered a request from The Post asking how far apart the candidates stood or details about the hall’s ventilation.

Moderator Chris Wallace estimated in an interview that he sat “10 or 12 feet” from Trump and the candidates were roughly eight feet apart onstage.

Forcefully projecting one’s voice — which Trump did in the direction of both Biden and Wallace, who was also unmasked — may propel virus particles farther than six feet. An outbreak among singers at a choir practice in Washington State, for instance, indicated the virus spread indoors up to 45 feet away from an infected person.

Which other world leaders have caught this virus?

Trump joins a small but growing number of world leaders and top officials who have contracted the coronavirus.

Boris Johnson, the British prime minister, was hospitalized for a week in April. He required oxygen and spent several days in the intensive care unit. Johnson has described covid-19 as the most serious danger to his health he had ever experienced.

Brazilian President Jair Bolsonaro, who had been dismissive of the virus’s severity even as the country’s infections climbed — Brazil ranks third by case count, after the United States and India — tested positive in July. Other leaders with positive test results include Belarus President Alexander Lukashenko and Honduras President Juan Orlando Hernández.

Canadian first lady Sophie Grégoire Trudeau also tested positive in March, and her husband, Canadian Prime Minister Justin Trudeau, self-isolated for 14 days at their residence, during which he continued to work.

Joel Achenbach and Laurie McGinley contributed to this report.