President Donald Trump was taken to Walter Reed hospital Friday evening after being diagnosed with COVID-19 late last night. For many patients, being hospitalized indicates they are on the edge of falling seriously ill, doctors say.

“If he went from being on the campaign trail to feeling sick yesterday to having a fever and now being hospitalized, I would be worried about him as a patient,” said Dr. Peter Chin-Hong, who has treated dozens of COVID-19 patients but isn’t privy to the President’s condition. “Hospitalization typically indicates a higher level of disease.”

White House press secretary Kayleigh McEnany said Friday the president “remains in good spirits and has mild symptoms.” 

“Out of an abundance of caution, and at the recommendation of his physician and medical experts, the President will be working from the presidential offices at Walter Reed for the next few days,” she said.

Trump is a high-risk COVID-19 patient because he is 74 and obese, said Chin-Hong, a professor of medicine and infectious disease specialist at the University of California, San Francisco. 

Given the high level of medical care available in the White House, Chin-Hong said it’s possible there were concerns he might need, or eventually need, oxygen.

“Once you require oxygen, that’s a bad omen,” he said.

Amesh Adalja, a senior scholar at Johns Hopkins University Center for Health Security, said White House medical staff likely monitor closely Trump’s vital signs and recommend appropriate care.

A hospitalization “would suggest they would need more aggressive monitoring, bloodwork or intravenous fluids,” said Adalja, an infectious disease and emergency medicine expert. “Or possibly the use of an experimental therapy that might require a hospital setting to be administered in.”

Other doctors not involved in the president’s care said his age, weight and gender put him at high risk. At 74, the president is five times more likely to be hospitalized and 90 times more likely to die of COVID-19 than someone between the ages of 18 and 29, according to the CDC.   

Adults with obesity have triple the risk of hospitalization due to a COVID-19 infection, according to the CDC. This is in part because obesity is linked to impaired immune function and decreased lung capacity and reserve. 

Going to the hospital is a very significant event for most COVID-19 patients and generally occurs when they require oxygen, Chin-Hong said.

“If you’re requiring oxygen, it indicates it’s more than just the virus, it indicates you’re dealing with inflammation from the virus,” he said. “That means you’re close to falling off the cliff.”

The progression into acute and dangerously severe COVID-19 can be very rapid and is something he’s seen in many patients.

“It’s very, very sudden. Somebody might be on very little oxygen and then they suddenly start needing a lot of oxygen. Usually, it’s not a gradual progression,” he said. “The patient is kind of trucking along and then all of the sudden they go south. That’s why we talk about ‘falling off the cliff’ with COVID.  You get wheeled to the ICU and you have lung injury most of the time.”

Once a patient is in the ICU they may still recover, but they’re likely to be hospitalized a while, Chin-Hong added. “If you live, people take a long, long time to recover.”