Philadelphia, Pennsylvania, and New Jersey officials said Thursday they will not follow new, more restrictive coronavirus testing guidelines from the Centers for Disease Control and Prevention denounced as insufficient by many public health experts.

People who have been exposed to someone with COVID-19 should be tested, even if they have no symptoms, Philadelphia Health Commissioner Thomas Farley said Thursday, adding that identifying people who have the infection is key to “stop[ping] the chain of transmission.”

He and Gov. Phil Murphy of New Jersey were among several leaders, including the governors of New York, Connecticut, Kentucky, Washington, and California, who said they were alarmed by the change and would not heed the guidance.

The Pennsylvania Department of Health will not change its testing guidelines either, and Gov. Tom Wolf’s administration is continuing to work on expanding testing availability, a spokesperson told The Inquirer.

The CDC’s new guidelines said it isn’t necessary for those who have been exposed to infected people to get tested if they don’t have symptoms. After that prompted sharp criticism on Wednesday, CDC Director Robert Redfield made a clarification Thursday, saying that “testing may be considered” for people who have been in close contact with someone with the virus.

The CDC had previously recommended testing for anyone who had been within six feet of an infected person for more than 15 minutes. Widespread testing has been a key component of the coronavirus response for most countries. People can transmit the virus even when they don’t feel sick, and the CDC estimated in July that 40% of people infected are asymptomatic.

President Donald Trump has repeatedly suggested the United States should do less testing without providing any scientific rationale, and in June told a rally that he asked his staff to slow down testing.

On Wednesday, the leading association of U.S. infectious-disease experts called for the CDC to immediately reverse the decision, and the American Medical Association said the guidelines were “a recipe for community spread and more spikes.”

Testing is not only used to stop someone from transmitting the virus, but also the percentage of tests that come back positive is a key indicator in how the virus is spreading and in guiding public health decisions about shutdowns and other measures.

Robust testing has been crucial in decreasing the spread of the virus, Murphy said in a joint statement with the governors of New York and Connecticut.

“This 180-degree reversal of COVID-19 testing guidelines is reckless, and not based on science and has the potential to do long-term damage to the [CDC’s] reputation,” they said in the statement. “This abrupt and ill-informed shift threatens the robust testing regimes our states have worked tirelessly to stand up with our federal partners.”

The governors noted that the CDC and Department of Health and Human Services had not provided scientific evidence for the policy change, something the AMA also called on the federal agencies to do.

Redfield said in his Thursday statement that everyone who needs a test can get a test, but said: “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.”

However, the CDC’s website still said people who have been exposed and don’t have symptoms “do not necessarily need a test unless you are a vulnerable individual or your health care provider or State or local public health officials recommend you take one.” The agency applied the same guidelines to asymptomatic people who live in an area of high virus transmission and have attended a gathering of 10 or more people without masks or social distancing.

Farley recommended that anyone who has been exposed to someone with the coronavirus wait about seven days after exposure before getting tested to ensure an accurate test result. But he said the public health goal for stopping the spread of the virus is to increase testing, not decrease it.

“As the case rates go down, testing for those people who have been exposed is even more important,” Farley said, “because we want to identify as many people with the infection as possible so that we can do contact tracing and stop the chain of transmission.”

Almost half of Philadelphia residents who catch the virus know whom they got it from — usually a household member, a relative, or a friend, the city has learned through contact tracing.

Testing yielded new information in the region Thursday: Less than 3% of the 3,200 Philadelphia test results returned within the last day were positive, and of the 151,008 tests administered statewide between Aug. 20 and Aug. 26, about 2.9% were positive, the Department of Public Health said. Those relatively low numbers indicate a slower spread.

“We see continued progress against the coronavirus epidemic with improving signs locally, regionally, and nationally,” Farley said.

In reporting new cases of the virus Thursday, Philadelphia confirmed 88, Pennsylvania 620, and New Jersey 374.

Less than two weeks into its fall semester, Bloomsburg University announced 90 cases of the coronavirus had been reported among students — and said it would switch to mostly remote instruction.

Elsewhere, no fans will be allowed at Eagles games until further notice, the Eagles said Thursday, saying the state and city had provided confirmation of the expected moratorium on spectators.

As autumn nears and preparation begins for the annual flu season to occur amid a pandemic, Wolf announced $10 million in grant funding for projects working on coronavirus vaccines, treatments, and therapies.

The money will go to 23 “promising” projects, including vaccines and treatments such as developing a protective antibody and determining whether cancer medication would help coronavirus patients.

“We know that the only way we can get back to our normal lives is by developing a robust testing and tracing infrastructure combined with effective, safe and affordable treatments and vaccines,” the governor said in a statement.

Farley said it is unknown what exactly the virus will do when late fall and winter arrive.

“It’s such a new virus,” he said. “Anything is possible.”

Staff writers Erin McCarthy, Rob Tornoe and Susan Snyder contributed to this article, which also contains information from the Associated Press.