The Centers for Disease Control and Prevention on Wednesday broadened the guidelines for coronavirus testing, allowing anyone who has symptoms like a fever, cough or difficulty breathing to receive a test if a doctor agrees.
The changes greatly expand the pool of patients who may qualify for diagnostic testing. But the nation’s testing capacity is still limited, and experts feared a rush by the worried well just as companies and hospitals are getting new laboratories off the ground.
A surge in coronavirus testing by people who have no real need may divert resources from seriously ill patients whose diagnosis is unknown. When the diagnosis is uncertain, experts noted, it is difficult to know how to use limited protective gear appropriately or whether to isolate the patient.
The loosening of testing criteria comes less than 24 hours after Vice President Mike Pence announced that federal health officials would lift all restrictions on access to testing. The new guidelines will “make it clear that any American can be tested, no restrictions, subject to doctors’ orders.”
The nation’s testing capacity is being expanded, now that private labs and companies are being allowed to make their own tests. But the process has only begun, and it will take time to ramp up the production of new testing kits.
The C.D.C. distributed its own diagnostic test kits to state and local health departments last month, but they turned out to be flawed, producing sometimes inconclusive results. The C.D.C. distributed partial replacements, but on Saturday the Trump administration announced that commercial and academic institutions would be permitted to make their own.
Officials with the Association of Public Health Laboratories said this week that member laboratories eventually would be able to conduct about 10,000 tests a day. On Tuesday, 54 labs were running at full capacity; 46 are expected to be up running by Saturday.
Laboratories around the country are still not ready to test large numbers of samples, several experts said. While the federal government has said it is shipping enough kits to test thousands of patients, some public health laboratories still have not received kits from the C.D.C., or are in the process of running checks to ensure they are working properly.
Once they are operating, the labs can process only about 100 tests per day.
Commercial tests — such as those developed by companies like Cepheid, Hologic and Qiagen — are expected to greatly increase capacity, but representatives for those companies said they were weeks away from approval by the Food and Drug Administration.
Hologic has said that once its tests are available, labs could run about 1,000 tests per day, but only if the labs did not also run other tests for other viruses, like the flu or H.I.V.
But demands for testing are already streaming in to laboratories in the Bay Area, where 30 coronavirus cases have been reported.
“We are already overwhelmed with calls day and night to get testing,” said Dr. Julie Vaishampayan, public health officer of Stanislaus County in Modesto, Calif.
Certain nonhospitalized patients were permitted to begin coronavirus testing on Tuesday. Public health laboratories in California are already working seven days a week, she said.
Previous guidelines for testing were much more restrictive, requiring a patient to have symptoms of respiratory illness as well as a clear route of exposure, such as recent travel to China or other affected countries, contact with a known coronavirus patient, or hospitalization with a severe and unexplained illness.
In the C.D.C.’s new guidance, doctors were encouraged to rule out other causes of respiratory illness, such as influenza, and to take into consideration whether there are other local coronavirus cases.
Doctors were also encouraged to consider testing for anyone — including health care workers — who had close contact with a known coronavirus patient within 14 days of developing symptoms, as well as anyone who traveled recently to China, Iran, Italy, Japan or South Korea.
Some experts worried that the pendulum had swung too far, from testing too few Americans to testing far too many, in just weeks. Federal health officials appear to have done away with virtually all requirements for testing.
“They’re not going to be able to test everyone, and if we let everyone through for testing, the people who really need it won’t be able to get it,” Dr. Vaishampayan said. “We can’t do that for the whole state — there’s 48 million people here.”
“There has to be some sort of prioritization,” she added.
As a general rule, screening for infectious diseases requires some sort of winnowing of potential candidates, experts said. The C.D.C.’s new criteria relegate the decision to test to individual physicians with little experience, and scant scientific evidence, about a new disease.
“You need some sort of framework within which to work,” said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University. “Not every patient who walks into the doctor’s office with a cough needs to be tested.”
Priority should be given to people who are involved in an investigation of an outbreak — as well as their contacts, and exposed health care workers — and to symptomatic people who have returned from trips to affected regions, Dr. Schaffner said.
People with symptoms who are at high risk for complications and severe illness because of underlying health conditions — such as Type 2 diabetes, heart disease and lung disease — should receive priority, as well as individuals who are older and frail.
Flu also should be ruled out before coronavirus testing is considered, Dr. Schaffner suggested.
There are more than 130 confirmed cases of coronavirus infection in 16 states in the United States, and 11 patients have died. So far, the majority of these cases are in California and Washington State, and many are related to travel outside the country.
Until last week, the C.D.C. refused to test patients for the novel coronavirus if they had not been to China recently or had contact with a known, identified patient.
A severely ill hospital patient in Sacramento waited days to get a coronavirus test approved, and then days more to get the test processed at C.D.C. laboratories in Atlanta.
Following mounting criticism, the agency’s diagnostic criteria were slightly loosened to allow testing of certain hospitalized patients who did not have a clear exposure to the coronavirus and to include four additional countries where the virus has taken root.