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Dr. Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, has started what he called a "modified quarantine" after came in contact with a White House staffer, who tested positive for COVID-19, according to CNN report, making him the third senior U.S. health official to go into isolation. 

But the member of the White House's coronavirus task force said he was not in close proximity to this person with the virus, adding he's at "low risk" and the test result came out negative on Friday.

It's not immediately clear which White House staffer Fauci had contacted with.

Fauci told CNN that he will stay at home and telework - though he might go to his office at National Institute of Allergy and Infectious Diseases, where he is the only one there - and wear a mask continually for 14 days.

Two other cabinet-level U.S. officials, Director of the Centers for Disease Control and Prevention Robert Redfield and U.S. Food and Drug Administration Commissioner Stephen Hahn were both in self-quarantine on Saturday after coming into contact with someone who had tested positive for COVID-19.