Trump, 74, who was flown to Walter Reed National Military Medical Center outside Washington on Friday, has taken two doses of a five-day course of the intravenous antiviral drug Remdesivir, as well as the steroid dexamethasone, which is used in severe cases.

Dr Sean P. Conley acknowledged on Sunday Trump’s blood oxygen levels had dropped in prior days and that he ran a high fever on Friday morning.

He admitted the president’s condition had been worse than previously disclosed but said it was now improving.

The briefing came the day after contradictory messages from the White House caused widespread confusion about the president’s condition.

Trump spent much of the year downplaying the risks of COVID-19, which has infected 7.4 million Americans, killed more than 209,000, and caused an economic downturn that has thrown millions out of work.

His illness has upended his re-election campaign as it seeks to fend off Democratic challenger Joe Biden in the final month of the race, and rattled financial markets.

Several members of his inner circle have also tested positive for the disease, as well as three Republican members of the US Senate.

Two members of the White House residence staff tested positive for COVID-19 a few weeks ago, and Trump’s “body man” aide, Nicholas Luna, has also tested positive, according to a source familiar with the situation.

The New Jersey Department of Health said on Sunday the White House had provided it with the names of more than 200 people who attended a Trump fundraiser at his golf club in Bedminster on Thursday, after the White House knew that adviser Hope Hicks had tested positive.

Asked what tests had revealed about the condition of Trump’s lungs, Conley replied: “There’s some expected findings but nothing of any major clinical concern.”

Conley’s response suggests the X-rays revealed some signs of pneumonia, said Dr Amesh Adalja, an infectious disease specialist at Johns Hopkins University.

“The expected finding is that he has evidence of pneumonia in the X-ray. If it was normal they would just say it is normal,” Adalja said.

Doctors said the president had a high fever on Friday morning but had not run a fever since Friday.

Dr Brian Garibaldi said Trump was given the steroid dexamethasone in response to “transient low oxygen levels”.

“He received his first dose of that yesterday and our plan is to continue that for the time being,” Garibaldi said.

Dexamethasone is known to improve survival for patients hospitalised with severe or critical COVID-19 who need extra oxygen.

But it should not be given in mild cases since it can limit the body’s own ability to combat the virus, according to guidelines from the Infectious Disease Society of America.

Trump is also being given an experimental treatment, Regeneron’s REGN-COV2, as well as zinc, Vitamin D, famotidine, melatonin and aspirin, his doctors have said.

“Our plan for today is to have him eat and drink, be up out of bed as much as possible, to be mobile,” Garibaldi said.

– Reuters