Joe Biden has again tested positive for COVID-19 in what doctors say may be a “rebound” infection.
The US president, 79, has “experienced no re-emergence of symptoms and continues to feel quite well”, White House physician Dr Kevin O’Connor said.
Mr Biden also tested positive nine days ago, on 21 July, when he was said to be “experiencing very mild symptoms”.
The second confirmation of the virus is believed to be a “rebound” experienced by some patients, Dr O’Connor said.
It is something that can be experienced by patients who have been treated with an anti-viral medication called Paxlovid – the drug the president received.
In a tweet, Mr Biden said two positive tests in close succession can happen to a “small minority of folks”.
He added: “I’ve got no symptoms but I am going to isolate for the safety of everyone around me.
“I’m still at work, and will be back on the road soon.”
The president had tested negative for the last four days, Dr O’Connor said.
Given Mr Biden’s lack of symptoms, there is no plan to reinitiate treatment, the medic added.
Mr Biden’s diary includes a trip to Michigan on Tuesday to promote new legislation to boost the semiconductor industry – a visit announced earlier on Saturday.
After his initial positive test, the White House said the president was continuing to carry out his duties “fully”.
Multiple members of the Biden administration and other senior figures in Washington have tested positive for the virus in recent months, including vice-president Kamala Harris, House of Representatives speaker Nancy Pelosi and Attorney General Merrick Garland.