Robert O’Brien, Trump’s National Security Adviser, Has the Virus

President Trump’s national security adviser, Robert C. O’Brien, has tested positive for the coronavirus, the administration said on Monday.

Mr. O’Brien, 54, “has mild symptoms” and is working remotely from “a secure location off site,” the administration said in a statement.

“There is no risk of exposure to the president or the vice president,” it said. “The work of the National Security Council continues uninterrupted.”

Mr. O’Brien is the most senior White House official known to have contracted the virus. He typically works from a West Wing office steps away from the Oval Office and, under normal circumstances, may see the president several times a day.

It is unclear when he was last in physical contact with Mr. Trump, although he joined the president on a July 10 trip to Florida.

Speaking to reporters before departing the White House on Monday afternoon, Mr. Trump said he had heard about Mr. O’Brien but did not know when he had tested positive. “I haven’t seen him lately,” the president added.

Mr. O’Brien also traveled to Paris in mid-July, where he met with several European security officials, visited an American war cemetery and attended a Bastille Day celebration. It was unclear whether he had become infected before or after that trip. The White House statement did not provide further details.

A photograph of Mr. O’Brien in Paris with his counterparts from Britain, France, Germany and Italy shows the men standing nearly shoulder to shoulder without masks, and Mr. O’Brien and others are not wearing masks in images of his ceremonial stops released by the White House.

Speaking to reporters at the White House on Monday, Larry Kudlow, Mr. Trump’s top economic adviser, said that Mr. O’Brien believed he had contracted the virus from his daughter. “Apparently it’s a light case,” Mr. Kudlow said.

Senior White House aides are tested regularly for the virus, as is Mr. Trump.

The development comes as Mr. Trump has begun to more frankly acknowledge the severity of the virus’s spread throughout the American South and West.

Mr. O’Brien assumed his job in September, succeeding John R. Bolton, who resigned after mounting conflicts with the president over foreign policy.

He is the latest of several White House staff members and others in the president’s orbit who have tested positive for the coronavirus. They include a military officer who works as a presidential valet at the White House, as well as Vice President Mike Pence’s press secretary, Katie Miller, both of whom tested positive in early May. Last week, the White House closed two cafeterias in its extended complex after an employee tested positive.

Mr. Pence postponed a planned trip to Arizona this month after members of his Secret Service detail tested positive or showed symptoms of the virus. Kimberly Guilfoyle, a former Fox News commentator who is dating Donald Trump Jr., also contracted the virus, as did several Trump campaign advance staffers who helped to arrange his June rally in Tulsa, Okla.

Mr. O’Brien’s deputy on the National Security Council, Matthew Pottinger, was among the first White House officials to wear a mask. He accompanied Mr. O’Brien on his trip to Paris this month.

The news of Mr. O’Brien’s infection resonated quickly across the world.

Hu Xijin, the editor of the nationalist Beijing newspaper Global Times, tweeted that the news about Mr. O’Brien, a leading China hawk in the administration, “shows the pandemic has been completely out of control in the US. No American is absolutely safe.”

“Novel coronavirus is truly US’ top enemy now,” he added.