An abrupt shift this week in government testing guidelines for Americans exposed to the novel coronavirus was directed by the White House’s coronavirus task force, alarming outside public health experts who warn the change could hasten the disease’s spread.

The new guidance — introduced this week, without any announcement, on the Centers for Disease Control and Prevention website — replaces advice that everyone who has been in close contact with an infected person should get tested to find out whether they had contracted the virus. Instead, the guidance says those without symptoms “do not necessarily need a test.”

Several leading infectious-disease experts predicted that, after months of public health exhortations encouraging people to get tested, the turnaround could heighten public confusion, impede contact tracing and lead to more cases. The nation’s society of infectious-disease doctors demanded the guidance be reversed as the United States leads the world in confirmed cases and deaths.

The CDC estimates that 40 percent of those who test positive for the coronavirus have no symptoms but may be highly infectious and spread it to other people.

The revised guidelines come as President Trump has feuded with the CDC and the Food and Drug Administration, both parts of the Department of Health and Human Services, and marginalized officials who would ordinarily play leading roles in a pandemic response. He has repeatedly said that he did not like that more testing had revealed more cases.

“I said to my people, ‘Slow the testing down, please!’ ” Trump said at a rally two months ago. Aides said he had been speaking tongue-in-cheek. But asked later whether he had been kidding, Trump replied, “I don’t kid.”

On Wednesday, Brett Giroir, an assistant HHS secretary who oversees testing, denied the impetus for the shift came from the White House. He said the idea of altering the testing guidance originated with him and CDC Director Robert Redfield, based on concerns that people can have misleading negative results if the test is given too early.

“They think it’s a badge of honor [to get a negative result] and go do what you are going to do,” he said in an interview, adding, “It’s much more important to focus on the actions people need to take,” including wearing masks and staying at safe distances from others.

A senior administration official, speaking on the condition of anonymity to share behind-the-scenes discussions, confirmed that Giroir launched the effort. Redfield was initially skeptical, the official said, “but then came along to it.”

“The cynical approach could be to say you have fewer tests, so you have fewer … cases,” the official added. “The truth, I think, is that people are getting tested who don’t really need to get tested. You are taking a test from someone who actually needs it and is at a greater risk.”

At least three high-profile Democratic governors said their states would not follow the new guidelines. “This will not be the policy of the state of California,” Gov. Gavin Newsom said in a tweet. Washington Gov. Jay Inslee said the guidance would cause his state “to miss thousands of new cases and allow the virus to spread in our communities.” On Twitter, he urged: “If you’ve been exposed to a confirmed case, GET TESTED.”

And New York Gov. Andrew M. Cuomo called the change “indefensible” in a phone call with reporters, CNBC reported. “We’re not going to follow the CDC guidance,” he said. “I consider it political propaganda.”
On a conference call with reporters, Giroir said he and Redfield discussed the idea with all the physicians on the White House’s coronavirus task force, including Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, and Scott Atlas, a new member influential with Trump from his appearances on Fox News who is a fellow at Stanford University’s conservative Hoover Institution. Atlas has said fewer people need tests for the virus, which has led to more than 5.7 million cases in the United States and more than 176,000 deaths. He is not an infectious-disease specialist.

“All the docs signed off on this … before it got to a place where the political leadership would have ever seen it,” Giroir said. He said the task force debated the change for about a month before approving it last Thursday.

Fauci contradicted aspects of that, however, in a statement he gave to CNN’s Sanjay Gupta. “I was under general anesthesia in the operating room last Thursday and was not part of any discussion or deliberation regarding these new testing recommendations … I am concerned about the interpretation of these recommendations and worried it will give people the incorrect assumption asymptomatic spread is not of great concern. In fact, it is.”

A NIAID spokeswoman confirmed Fauci’s views, noting he had quickly reviewed a version of the guidelines that circulated” before his surgery and “was not struck by the potential implication of this particular change” until he saw the final guidance.

In its new form, the testing guidance says that people who have been within six feet of an infected person for at least 15 minutes do not necessarily need a test unless they are especially vulnerable to the virus, or one is recommended by state or local public health officials or their health providers.

It also no longer calls on people to self-isolate for two weeks, the time frame within which most people develop coronavirus symptoms. Rather, it says those who have been in close contact with an infected person and have no symptoms “should strictly adhere to CDC mitigation protocols,” such as mask-wearing and social distancing. Giroir said in the interview that anecdotal evidence suggests such practices are effective at limiting virus transmission, even if people go out on occasion.

In a statement late Wednesday, the CDC’s Redfield said the new guidelines prioritize testing individuals with symptomatic illness, significant exposure to the virus, vulnerable populations including nursing homes residents, health care workers and essential workers.

“Everyone who needs a covid-19 test, can get a test,” he asserted. “Everyone who wants a test does not necessarily need a test; the key is to engage the needed public health community in the decision with the appropriate follow-up action.”

Many in the medical community condemned the changes.

“Suggesting that people without symptoms, who have known exposure to covid-positive individuals, do not need testing is a recipe for community spread and more spikes in coronavirus,” said Susan R. Bailey, president of the American Medical Association, calling on the federal government to release the scientific rationale for the change.

Former CDC director Tom Frieden said that with testing materials and labs’ capacity stretched thin, it makes sense to set priorities for who needs to get tested the most. “But that’s not what they’re saying,” he said. “They’re saying don’t test asymptomatic people … There’s a big difference between not testing asymptomatic college students and not testing contacts” of an exposed person. He noted that people who are asymptomatic are able to spread the virus to others before they develop symptoms. “We don’t know what proportion of all spread comes from people who are asymptomatic,” Frieden said. “We know it’s not negligible.”

Others said the change, while controversial, might have merit if it were properly explained to the American public.

Jennifer Nuzzo, an epidemiologist at the Johns Hopkins Center for Health Security, criticized the administration for releasing important recommendations under the CDC name without allowing its officials to discuss them. She also said the White House intervened in the drafting of CDC guidance about masks and reopening of churches and schools, so “that process has really poisoned people’s view of guidelines, quite unfortunately.”

Nuzzo said she and other public health experts have called for the administration to prioritize who gets tested. She added, however, that people who have been in contact with known cases should be included among the priorities.

Physicians leading clinical trials for covid-19 treatments said the change could slow down that urgent quest, particularly for those with mild and moderate illness. To recruit people to those trials, physicians need potential participants to be identified early in their disease course.

“A lower number of diagnostic tests, period, makes it much more difficult to conduct outpatient clinical trials, where we’re trying to find a solution so society can begin to function again,” said David Sullivan, a professor of molecular microbiology and immunology at the Bloomberg School of Public Health at Johns Hopkins University who is leading a trial to see if convalescent plasma is an effective early treatment for covid-19 patients.

Others questioned whether the new guidance could mean that children, who are mostly asymptomatic, will be less likely to be tested.

Giroir said he does not expect the change to lead to any fewer coronavirus tests being performed, particularly as students return to school and workers to their jobs.

Carolyn Y. Johnson, Yasmeen Abutaleb and Josh Dawsey contributed to this report.