President Biden canceled his face-to-face meetings with Prime Minister Micheal Martin of Ireland on Thursday after the prime minister received a positive result on a coronavirus test during a gala event in Washington on Wednesday night that both men attended.

The two leaders instead met virtually on Thursday morning.

Daniel Mulhall, Ireland’s ambassador to the United States, confirmed the positive test early Thursday, complicating the prime minister’s plans to spend the day with Mr. Biden for traditional St. Patrick’s Day celebrations.

Mr. Biden, who is 79 and has been vaccinated and boosted, had been scheduled to meet with Mr. Martin at a morning meeting at the White House, followed by a luncheon at the Capitol and a shamrock presentation at the White House. Mr. Biden attended the luncheon and officials said he would still participate in the St. Patrick’s Day celebration. During their virtual morning meeting, Mr. Biden was seated near a television monitor showing Mr. Martin, with a bowl of shamrock on a coffee table. The president said he was “deeply sorry for the inconvenience” for the virtual format.

White House officials said that Mr. Biden was not in close contact with Mr. Martin during Wednesday’s gala, which the Centers for Disease Control and Prevention defines as being within six feet of someone for at least 15 minutes.

The prime minister’s test result came amid a burst of infections among public officials in Washington in recent days. At least nine Democratic members of Congress tested positive this week after a party retreat and late night voting last week. Douglas Emhoff, the husband of Vice President Kamala Harris, also tested positive this week, as did former President Barack Obama.

White House officials have downplayed the recent spate of cases, noting that the overall rate in Washington is still extremely low. Jen Psaki, the White House press secretary, said on Monday that the United States was in a better position to combat the Omicron subvariant known as BA.2, because of the number of people vaccinated.

“It’s circulated in the United States for some time,” she said of the new variant. “We’ve been watching it closely, of course.”

Mr. Mulhall said on Twitter that he had accepted a leadership award for Mr. Martin on Wednesday at the gala for the Ireland Funds in Washington, an event that Mr. Biden and Speaker Nancy Pelosi also attended.

“I filled in for the Taoiseach after he tested positive for #Covid19,” he wrote, using the Irish word for the country’s leader. “I wish the Taoiseach well for his recovery.”

The speaker’s office confirmed that Ms. Pelosi, who is vaccinated and boosted, had tested negative on a P.C.R. test on Thursday morning, and would continue regular testing and to follow C.D.C. guidelines, though it was not clear which ones. It was unclear whether the Attending Physician’s Office considered Ms. Pelosi, 81, to be a close contact.

Ms. Pelosi, who was photographed sitting next to Mr. Martin during the gala, appeared at her weekly news conference on Thursday, adding that she was tested nearly every day. Mr. Martin remained masked until food was served, she said, and was pulled aside during the appetizer course about his positive test.

“We’re very, very sad that on St. Patrick’s Day, the Taoiseach has this diagnosis,” she said at her indoors news conference, where she removed her mask to speak and take questions. “We won’t be able to have the benefit of the honor of his presence.”

A scheduled lunch — The Friends of Ireland Lunch on Capitol Hill — proceeded on Thursday, without Mr. Martin present.

Irish journalists traveling with Mr. Martin’s delegation reported that he had attended the early part of the gala, and photos from the event appeared to show him seated next to Ms. Pelosi.

A spokesperson for the Irish government said in a statement on Thursday that the prime minister had tested negative for the virus earlier on Wednesday and also on Sunday, before traveling to the United States.

His second test on Wednesday was administered after a member of the prime minister’s delegation received a positive result on a test, the statement said.

Mr. Mulhall did not elaborate on whether Mr. Martin had symptoms.

In a tradition going back to 1952, Irish ambassadors or political leaders present the American president with a bowl of shamrocks on or around St. Patrick’s Day, usually in the White House. The tradition is valued in Ireland, and by many Irish Americans, as a sign of the close ties between the two countries.

Mr. Martin may now never visit the Oval Office in this official capacity: His first scheduled visit last year was canceled because of the pandemic and, as part of a coalition deal with two other Irish political parties, he is expected to hand over the prime ministership before next March.

On Wednesday, Claire Cronin, the U.S. ambassador to Ireland, said on Twitter that she canceled her plans to join Mr. Martin because she had tested positive for the coronavirus.