Just as the nation’s ability to test for coronavirus is expanding, hospitals and clinics say another obstacle is looming: shortages of testing swabs and protective gear for health care workers.

At the UCSF Health — a San Francisco hospital system at the heart of one of the nation’s coronavirus outbreaks — officials said they would have to stop testing patients in about five days because they will run out of nasopharyngeal swabs, which are inserted into patients’ nasal passages to get samples for testing. Other hospitals elsewhere in the country were ending their practice of using a second swab to test for the flu in an effort to preserve their supply.

The main manufacturer of the swabs, Copan, is an Italian company whose manufacturing plant is in Northern Italy, a region that has itself been hard hit by the coronavirus outbreak. It says it has ramped up manufacturing to deal with the extraordinary demand for an otherwise unassuming product to which many doctors gave little thought, until now.

“We weren’t really thinking about, ‘Wow, what’s our swab supply?’ because we haven’t really faced anything that depleted our swabs before,” said Dr. Josh Adler, the chief clinical officer of U.C.S.F. Health. Making matters more difficult, the swabs must have just the right ingredients — the shafts cannot be wood, for example — or the virus might not be properly detected. “You can’t go to your local store and get Q-tips,” he said.

On Wednesday, UCSF Health said it had secured another two-day supply of swabs.

Dr. Ulrike Sujansky, a physician in solo private practice in San Mateo, Calif., one of the areas with the most cases, said she has only been able to test a few patients because of problems with supplies.

“We cannot test. We cannot test,” she said. The swab kits she ordered from the two biggest lab companies, LabCorp and Quest Diagnostics, either arrived late or were not the right type, she said. She also does not have adequate masks or protective supplies, despite weeks of efforts to purchase them and recent appeals to state and local health authorities and hospitals. “I’m not given any tools to deal with this complete crisis.”

After a botched rollout of coronavirus tests in February, the Trump administration has tried to quickly expand the number of tests available to Americans by lowering regulatory hurdles and approving commercial tests made by companies — like Roche and Hologic — whose machines can run thousands of samples a day. Major lab companies like LabCorp and Quest Diagnostics have been ramping up their capacity, as have hospital labs around the country.

But shortages like those with the supply of swabs now threaten that broader testing effort. Premier, which buys medical supplies on behalf of many U.S. hospitals, said its members were also encountering problems.

“Our hospitals are eager to do their part to help expand access to testing, but are struggling to do so absent necessary testing supplies,” said Soumi Saha, the senior director of advocacy at Premier. She said that the company requested additional information from the F.D.A. about how to address the swab shortage days ago, but has not heard back.

On Wednesday, the Food and Drug Administration said in a statement, “We have heard concerns from labs who have questions about the availability of certain supplies. We are updating frequently asked questions for labs and test developers, providing information on alternative sources of reagents, extraction kits, swabs and more.” The agency said it also set up a toll-free line, 1-888-INFO-FDA, to help labs with questions about approvals or supplies.

Gabriela Franco, a spokeswoman for Copan, which makes the testing swabs, said the company has increased production at its plant in Brescia, Italy, to 24 hours a day, seven days a week. “We are asking our customers and distributors to rationalize their ordering so we can maximize throughout,” she said, adding that in the United States, a busy flu season had already depleted supply. The company has about half of the market for testing swabs in the United States.

She said the lockdown in Italy — which has been hit particularly hard with more than 2,500 deaths — — had not affected the business or the export of goods.

She said the company was taking precautions to protect its workers and to keep production running. “We are working with the Italian regional and national authorities to preserve the current manufacturing conditions in order to serve the world with our products, even in case heavier restrictions are applied,” she said.

The swab shortfall is just one example of the strain on the supply chain amid global demand for testing for coronavirus. Testing has also been hampered by dwindling supplies of RNA extraction kits, which are needed to extract the RNA from samples in order to run the tests in many cases. In response, the F.D.A. has widened the number of extraction products that can be used in the tests.

A shortage of masks, gowns and other protective gear — which has put a strain on many other areas of care — is also getting in the way of testing. Patients often sneeze or cough when the swab is inserted deep into their noses, which can expose the workers who are doing the tests to the virus.

“That’s been the bottleneck for what I call the crisis within the crisis,” said Dr. Christopher Crow, the president of Catalyst Health Network, who is setting up drive-through testing in locations around North Texas. His network of more than 800 physician offices serves one million people.

Until Tuesday, Dr. Crow was experiencing such a shortage of masks and other gear that he was facing the possibility of closing the sites Wednesday, just as he was preparing to vastly expand his capacity from about 30 people a day.

“You can’t go scuba diving without oxygen, a regulator and a mask,” he said. “If you don’t have that equipment to test, then you can’t test.”

On Tuesday afternoon, he learned that he had been granted permission by a regional authority to use a shipment of gear from the national stockpile, solving his problem, for now.

Some patients say the shortages have prevented them from getting tested, even when they are showing symptoms of the coronavirus. Aliesha O’Raw, a graduate student in Durham, N.C., said her primary care doctor sent her to an urgent care clinic after she had a fever and a dry cough for two weeks.

Ms. O’Raw, who is 26, has asthma and Ehlers-Danlos syndrome, an inherited condition that affects the body’s connective tissues, like skin and joints. Both are underlying conditions that could make the disease more severe. She tested negative for the flu, and antibiotics did not work.

When she visited the urgent care clinic on Monday, the doctor declined to test her because there was a shortage of swabs and they were rationing, she said. Because she did not have known contact with an exposed person, she was denied a test.

She would like to be tested “not for my own knowledge,” she said. “It’s that I know I have people around me who are starting to get sick.” Her boyfriend, who ran errands for her while she was ill, is now sick, she said, as are some classmates who were around her before she developed symptoms.

Her doctor ordered another test, and she was able to use a drive-through testing site that just opened. She was tested on Wednesday and is awaiting her results. “It’s happening,” she said. “It’s just taking longer than either of us expected.”

Sheri Fink contributed reporting.

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