The testing shift, experts say, was a far more puzzling reversal. Dr. Giroir said the move was “discussed extensively by” members of the White House coronavirus task force, and he named Dr. Redfield, Dr. Atlas, Dr. Fauci and Dr. Stephen M. Hahn, the commissioner of food and drugs. Notably, he did not name Dr. Deborah L. Birx, the White House coronavirus response coordinator. But he said Dr. Fauci was among those who had “signed off.”
In a brief interview, Dr. Fauci said he had seen an early iteration of the guidelines and did not object. But the final debate over the revisions took place at a task force meeting on Thursday, when Dr. Fauci was having surgery under general anesthesia to remove a polyp on his vocal cord. In retrospect, he said, he now had “some concerns” about advising people against getting tested, because the virus could be spread through asymptomatic contact.
“My concern is that it will be misinterpreted,” Dr. Fauci said.
The newest version of the C.D.C. guidelines, posted on Monday, amended the agency’s guidance to say that people who had been in close contact with an infected individual — typically defined as being within six feet of a person with the coronavirus and for at least 15 minutes — “do not necessarily need a test” if they do not have symptoms.
Exceptions might be made for “vulnerable” individuals, the agency noted, or if health care providers or state or local public health officials recommended testing.
Dr. Giroir said the new recommendation matched existing guidance for hospital workers and others in frontline jobs who have “close exposures” to people infected with the coronavirus. Such workers are advised to take proper precautions, like wearing masks, socially distancing, washing their hands frequently and monitoring themselves for symptoms.
He argued that testing those exposed to the virus was of little utility, because tests capture only a single point in time, and that the results could give people a false sense of security.