Biden is still testing positive for COVID. How long will he isolate?

President Joe Biden is still testing positive for COVID-19 four days into his rebound infection, White House physician Dr. Kevin O'Connor reported Wednesday.

Biden "continues to feel well," O'Connor said, noting the exam was conducted after the president completed a light workout.

"He is still experiencing an occasional cough, but less frequently than yesterday. He remains fever-free and in good spirits," O'Connor wrote. Biden's temperature, pulse, blood pressure, respiratory rate and oxygen saturation also remain normal.

O'Connor said Wednesday that Biden will continue to follow strict isolation measures, but it's not clear if he will go beyond the recommendations laid out by the Centers for Disease Control and Prevention -- as the White House vowed to do the first time he tested positive.

Biden initially tested positive for the virus on July 21, and emerged from isolation after completing a five-day course of Paxlovid and testing negative. But on July 30 he tested positive again in what O'Connor called "rebound positivity" -- referring to a relapse of COVID-19 some patients experience after taking the antiviral treatment.

The White House said after Biden's initial diagnosis that he would end isolation only after testing negative on an antigen test. The CDC recommends that an individual stop isolating after five days if they are fever-free and symptoms are improving. It doesn't suggest testing within 90 days of a positive case unless new symptoms develop.

For Biden's rebound case, the White House has said the president would again isolate for five full days, but it hasn't said if he would end isolation only after testing negative.

White House press secretary Karine Jean-Pierre told ABC News' Ben Gittleson on Wednesday she couldn't say if that would be the case.

"I would have to check to see exactly what the CDC guidance is, but we are gonna follow CDC guidance," she said.

When asked if the White House wants the CDC to urge Americans to test to end isolation, too -- and if they want the public to use the president's behavior as a model -- Jean-Pierre said they'll "leave it to the experts."

"That is for the experts and they follow the science which changes on this," she said. "You know, this is COVID, as we know, once-in-a-generation pandemic, so we leave it to them to make that decision."

Thursday will mark Biden's fifth day of isolation after testing positive the second time.