Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, entered a "modified quarantine" due to exposure to someone who tested positive for the novel coronavirus.
He joins a growing list of administration officials taking precautions following the news of two known coronavirus cases at the White House, including the vice president's press secretary.
The Centers for Disease Control and Prevention Director Dr. Robert Redfield announced Saturday afternoon he would be going into self-quarantine due to "low risk exposure" to someone with the novel coronavirus. Food and Drug Administration Commissioner Dr. Stephen Hahn said he would be isolating himself for similar reasons.
The NIAID said Fauci tested negative for COVID-19 and is considered to be "at relatively low risk based on the degree of his exposure." Fauci's quarantine was described as "modified" and he might still go to his office at the National Institutes of Health, where he would be the only one in the building.
"Nevertheless he is taking appropriate precautions to mitigate risk to any of his personal contacts while still allowing him to carry out his responsibilities in this public health crisis," NIAID told ABC News.
Fauci, Redfield, Hahn and Assistant Secretary for Health Adm. Brett Giroir, the top official on testing, are scheduled to appear before the Senate Committee on Health, Education, Labor and Pensions Tuesday -- and though Fauci was planning to attend the hearing in person -- Chairman Lamar Alexander announced they will all do so via video conference.
"After consulting with Dr. Fauci, and in an abundance of caution for our witnesses, senators, and the staff, all four Administration witnesses will appear by videoconference due to these unusual circumstances," according to a statement from the senator's office.
Hahn and Redfield would have regularly come in contact with Vice President Mike Pence and President Donald Trump in consulting with the White House coronavirus task force. Both men have been tested multiple times and come back negative, though it's unclear if they've been tested again this weekend.
An FDA spokeswoman confirmed Saturday morning that Hahn was tested after he came into contact with an individual who tested positive. His test came back negative and he told his staff in a note that he would self-quarantine for two weeks as a precaution.
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The CDC said in a statement that if Redfield needs to go to the White House to fulfill any responsibilities for the task force, he would follow safety practices established for critical infrastructure workers who may have been exposed to COVID-19.
"Those guidelines call for Dr. Redfield and anyone working on the Task Force at the WH to have their temperature taken and screened for symptoms each day, wear a face covering, and distance themselves from others," the agency said in the statement.
Trump said on Friday he would "probably" have another test after a military service member -- a personal valet who had brought him Diet Cokes in the Oval Office -- had tested positive.
Pence's press secretary, Katie Miller, who's married to top Trump policy adviser Stephen Miller, also was revealed to have tested positive for the coronavirus on Friday.
Stephen Miller, one of the president's closest advisers, tested negative for COVID-19, ABC News has learned.
It is not clear who tested positive for coronavirus and came into contact with Fauci, Redfield and Hahn.
What to know about the coronavirus:
- How it started and how to protect yourself: Coronavirus explained
- What to do if you have symptoms: Coronavirus symptoms
- Tracking the spread in the U.S. and worldwide: Coronavirus map
This report was featured in the Monday, May 11, 2020, episode of “Start Here,” ABC News’ daily news podcast.
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