The four-day delay in testing a California woman for coronavirus highlights how a faulty test and, until Thursday, a narrow definition of who should be tested have hindered the United States’ ability to track how widely the disease has spread. Infectious-disease experts worry the disease may be spreading undetected in other places.

Those concerns were stoked by the emergence of the nation’s first case of community transmission in Northern California, where hospital administrators contend the patient, a woman, was not tested when clinicians requested it because she did not meet strict Centers for Disease Control and Prevention criteria that recommended testing only those with symptoms who recently returned from China, or who had close contact with a person confirmed to be infected with covid-19.

“We have just a few hundred testing kits in the state of California,” Gov. Gavin Newsom (D) said Thursday at a news conference. “That’s simply inadequate to do justice to the kind of testing that is required to address this issue head on. . . . Testing protocols have been a point of frustration for many of us.”

“You don’t know what you don’t know unless you’re testing,” he added.

The CDC put out a statement Thursday night disputing that it had denied doctors’ request to test the California woman.

“A preliminary review of CDC records indicates that CDC was first informed about this case on Sunday, Feb. 23, said the statement from spokeswoman Kristen Nordlund. “That same day, CDC requested specimens from the patient to test for covid19 exposure. Test results were confirmed and communicated on Wednesday.”

The problems underscored by the California case include the limited availability of tests — which were shipped out to labs nationwide with a problematic component that is only now being corrected — and the federal testing criteria, which had become outdated as the outbreak evolved from being centered in China to spreading in more than three dozen countries. On Thursday, the CDC also expanded federal guidelines to include testing for people who have unexplained severe respiratory symptoms that require hospitalization and people with symptoms who have recently traveled to Iran, Italy, Japan or South Korea.

Newsom said the state was working with the CDC to get more testing kits and the ability to do tests without shipping samples across the country.

“There’s a desperate need to do more testing,” said Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health. “The point is to find out if, like many other countries, we have undetected chains of transmission that we’re just not detecting.”

While Lipsitch said that Guangdong province in China had conducted more than 300,000 tests in fever clinics, the United States has tested 445 people, not including those who were evacuated. Health and Human Services Secretary Alex Azar said Thursday that 3,600 tests have been run but did not clarify how many people had received them.

In addition, the tests sent out nationwide earlier this month had a faulty component that has required most samples to be sent to the CDC in Atlanta for analysis. There were signs Thursday that federal health officials were correcting those problems. As of 9 a.m. Thursday, Scott Becker, executive director of the Association of Public Health Laboratories, said he was aware of only eight public health labs currently able to run tests but that about 40 more labs are expected to come online very shortly. And he said he expected all 100 public health labs across the country to be able to run tests by the end of two weeks.

Infectious-disease experts and others had been calling for the expanding of testing criteria for some time.

“It’s long overdue that [testing criteria] be broadened,” said Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security. He said the reason testing should include people with unexplained symptoms is because “travel history will become less important as we have community spread in countries around the world, as well as perhaps in the United States.”

He also said that it is important to test people with mild symptoms; right now, the emphasis is on those with lower respiratory symptoms, including coughing or shortness of breath, versus symptoms such as runny noses and sore throats. “But testing people with milder symptoms will give us an understanding of how widespread this is in the community,” Adalja said.

Hawaii Lt. Gov. Josh Green, who is an emergency physician, gave the example of a person who arrived in his state with flulike symptoms earlier this week from Las Vegas.

“Very likely, he had the flu; he hadn’t been in a region of concern for a full month, but it would have been very convenient to test,” Green said.

Some people who have fallen ill with what they fear may be the coronavirus are also upset they haven’t been able to get tested because they haven’t met the CDC criteria.

A 57-year-old woman who lives in New York City said that her husband developed a severe sore throat after returning from a business trip to South Korea in mid-February. He got a strep test, which came back negative. Ten days later, she got sick, with many more symptoms, including aches and pains, headache, congestion, and fever. Her doctor wanted her tested for the coronavirus, but she wasn’t eligible because she hadn’t traveled to a country with widespread transmission or been in contact with someone known to be infected.

“The testing needs to be broadened,” said the woman, who spoke on the condition of anonymity, citing privacy concerns. “If you don’t test, you don’t find. This is irresponsible.”

The woman said she has decided to self-quarantine for several days but worries that other people might not suspect they are infected and will pass on the virus. “It’s a Catch-22 that will put the weak and elderly at risk,” she added.

Jeff Engel, executive director of the Council of State and Territorial Epidemiologists, said that the tests not working has been the biggest impediment, in part because public health officials need to gain experience using them as they ramp up.

“I think the biggest disappointment was not getting field experience on laboratory testing,” Engel said. “We’ve already lost two weeks on that, and I think that was the biggest blow to progress.”

Officials are taking steps to try to fix the test. One of the three reagents, or components of the test, was giving inconclusive results when many laboratories were trying to verify that it was working. Public health labs received guidance late Wednesday afternoon that would allow them to go ahead with tests using two of the three components, if they were able to get those working. New test kits are expected to be sent out to labs next week.

Amy Goldstein contributed to this report.

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