Ms Hope Hicks, one of US President Donald Trump's closest aides, has tested positive for coronavirus infection, according to people familiar with the matter.
There was no indication that the president has contracted the virus, the people said. Ms Hicks travelled with Mr Trump aboard Air Force One to and from the presidential debate on Tuesday (Sept 29).
The people asked not to be identified because Ms Hicks's infection has not been publicly announced. Messages left for Ms Hicks were not immediately returned.
Ms Hicks is the latest person in Mr Trump's orbit to contract the virus, which has infected more than 7.2 million Americans and killed more than 200,000.
Other senior staff have contracted Covid-19 and recovered including National Security Adviser Robert O'Brien, but few spend as much time with the president as Ms Hicks, whose service dates to his 2016 campaign.
Some people close to Ms Hicks were told that she is experiencing symptoms of the disease.
"The president takes the health and safety of himself and everyone who works in support of him and the American people very seriously," White House spokesman Judd Deere said in a statement.
"White House Operations collaborates with the physician to the President and the White House Military Office to ensure all plans and procedures incorporate current CDC guidance and best practices for limiting Covid-19 exposure to the greatest extent possible, both on complex and when the president is traveling."
The development is likely to inflame criticism of the Trump administration's reaction to the coronavirus pandemic, as well as the president's disregard for public health measures to combat it.
Mr Trump seldom wears a mask and has belittled his re-election challenger, Mr Joe Biden, for routinely covering his face. The president has resumed holding large campaign rallies at which thousands of his supporters gather, shoulder to shoulder, few in masks.
Most of the events are held outdoors at airports but two recent events in Arizona and Nevada were indoors, a setting that public health experts raises the risk of virus transmission.
Ms Hicks travelled with Mr Trump to his debate with Mr Biden on Tuesday and to a Minnesota rally on Wednesday. Mr Trump's entourage entered the debate hall without face coverings, or removed them as they sat down, and refused an offer of masks from a doctor at the Cleveland Clinic, which was co-hosting the event.
Mr Biden's guests wore masks.
Ms Hicks was seen on Tuesday riding maskless in a staff van with White House senior adviser Stephen Miller, campaign adviser Jason Miller and others.
When they returned to Washington on Tuesday, Mr Stephen Miller and Ms Hicks were seen sharing an umbrella as they exited Air Force One in the rain.
Mr Miller's wife, Ms Katie MillerVP Mike Pence's press secretaryrecovered from Covid-19 earlier this year.
Mr Trump is tested regularly for infection, though is not clear precisely how often. People who work in the White House are tested daily, including members of the press corps, and anyone scheduled to meet with the president is tested beforehand.
Mr Trump's staff wear masks when travelling with him aboard the presidential helicopter, Marine One, and Ms Hicks observed that protocol this week.
But his aides worry that Mr Trump's lack of sleep during the final stretch of the campaign could leave him especially vulnerable to infection. The president did not return to the White House until after midnight following his Tuesday and Wednesday trips. Mr Trump's age, 74, also puts him at greater risk for serious illness from the virus.