Hope Hicks, one of United States President Donald Trump's closest aides, has tested positive for Covid-19, according to unnamed sources aware of White House happenings.

Hicks, 31, travelled with Trump aboard Air Force One to and from the presidential debate on Sep. 29.

However, there was no indication that the president has contracted the virus, people in the know said.

Hicks's infection has not been publicly announced, so sources asked not to be identified.

Hicks has not commented.

Hicks is the latest person within Trump's circle to contract the virus.

Some people close to Hicks were told that she is experiencing symptoms of the disease, Bloomberg reported.

Hicks travelled with Trump

Hicks travelled with Trump to his debate with Biden on Tuesday and to a Minnesota rally on Wednesday.

Hicks was seen on Tuesday riding maskless in a staff van with White House senior adviser Stephen Miller, campaign adviser Jason Miller and others, Bloomberg reported.

When they returned to Washington on Tuesday, Stephen Miller and Hicks were seen sharing an umbrella as they exited Air Force One in the rain.

Miller's wife, Katie Miller, who is Vice-President Mike Pence's press secretary, recovered from Covid-19 earlier this year.

Trump's staff wear masks when travelling with him aboard the presidential helicopter, Marine One, and Hicks observed that protocol this week.

Other senior staff have contracted Covid-19 and recovered.

National Security Adviser Robert O'Brien was one of them.

But Hicks has spent much more time with the president.

She has been with the president since his 2016 campaign.

Trump during debate

Trump's entourage did not have face coverings when they entered the debate hall on Tuesday, or removed them as they sat down.

They also refused an offer of masks from a doctor at the Cleveland Clinic, which was co-hosting the event.

Biden's guests wore masks.

Trump likely to be criticised

The Trump administration's response to the Covid-19 pandemic will likely be criticised.

The president's disregard for public health measures to combat Covid-19 has come under fire since the start of the year.

Trump seldom wears a mask and has mocked Biden for routinely covering his face.

The president has resumed holding large campaign rallies where his supporters gather unmasked.

Most of the events are held outdoors at airports but two recent events in Arizona and Nevada were indoors.

Trump's lack of sleep during the final stretch of the campaign could leave him vulnerable to infection.

Trump's age, 74, also puts him at greater risk of Covid-19.

Covid-19 has infected more than 7.2 million Americans and killed more than 200,000.

White House statement

"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."

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Top photo via CBS Los Angeles