The top official in charge of the U.S. Agency for International Development, John Barsa, has tested positive for the coronavirus, U.S. officials said.

Barsa, who leads one of the world’s largest aid organizations, has been isolating since he began exhibiting symptoms late Monday, USAID spokeswoman Pooja Jhunjhunwala said in a statement.

“While I do feel tired, I continue to monitor work virtually,” Barsa said in a memo to staffers obtained by The Washington Post. “The Agency’s COVID-19 Readiness Unit is notifying any individuals with whom I have met over the past 2 days.”

He noted that his offices would be “deep-cleaned” and closed until Monday.

Barsa held meetings in his office on Monday, said people familiar with the situation. He has a reputation for sparse mask use, which will probably result in those he met with having to quarantine on Thanksgiving as families around the country gather, the people said.

Jhunjhunwala said the agency takes “seriously the guidelines for safety protocols and physical distancing issued by the Centers for Disease Control and Prevention.”

Barsa, who holds the title of acting deputy administrator, canceled a planned trip to Honduras on Sunday as a result of his condition, said a person familiar with the situation who like others spoke on the condition of anonymity to discuss internal agency matters.

In recent days, Barsa had told USAID colleagues that the agency would not cooperate with the transition to President-elect Joe Biden’s administration until a Trump appointee signed paperwork affirming him as the winner of the election.

That formality came on Monday and directed all federal agencies to provide post-election resources to the incoming administration. USAID has yet to publicly acknowledge the decision even though some officials have begun to work with Biden’s team on the transition.

Barsa has retained his job as head of the agency because of a decision by the White House to fire a senior USAID official, Bonnie Glick, this month without cause. Barsa was not confirmed by the Senate to lead USAID, and the Federal Vacancies Reform Act limits the amount of time officials can perform such functions without congressional approval. The White House’s decision to fire Glick, who was deputy administrator of USAID, however, extended Barsa’s grip on power.