US first lady Jill Biden has tested positive in a rebound case of COVID but is not experiencing any symptoms, while President Joe Biden continues to test negative, officials say.

Dr Biden tested positive on Wednesday (local time) by antigen testing, following a negative test the previous day, and the White House’s medical unit has notified close contacts, her deputy communications director said.

“The first lady has experienced no re-emergence of symptoms, and will remain in Delaware, where she has re-initiated isolation procedures,” her deputy communications director Kelsey Donohue said in a statement.

Dr Biden, 71, first tested positive for the virus on August 16.

She had ended her first isolation on August 21 after a course of Paxlovid, an antiviral medication.

Mr Biden tested negative for COVID on Wednesday morning in antigen testing, the White House said.

A White House official said the president would wear a mask for 10 days when indoors and near others.

The White House will also maintain Mr Biden’s increased cadence of testing and report those results, the official said.

Mr Biden recently also suffered a rebound case of the virus, after being confirmed with it for the first time several weeks ago. Medical experts say rebound cases of the virus are not uncommon after taking Paxlovid.

-with AAP