Americans seeking coronavirus tests amid an unprecedented surge in cases are experiencing lengthier lines and waiting days to get test results — delays that complicate efforts to slow the pandemic and that are expected to intensify as people try to get tested ahead of family gatherings.

Testing sites from New York to Wisconsin to Oregon are reporting lines stretching three to four hours, with results taking as long as five days.

In Denver, officials shut down one testing site within an hour of opening Tuesday because it had reached capacity. At another site, lines grew so long that officials closed over concerns about traffic safety. In New York, residents are standing in line for hours. In Olympia, Wash., officials have had to turn away as many as 200 cars in line in recent days because labs had reached capacity.

When Sarah Hass, 22, recently tried to book a coronavirus test in the Chicago suburbs, she couldn’t find a clinic with an open appointment in the next three days. She widened her search to any CVS or Walgreens within a two-hour drive. Still nothing.

Finally, she headed to a drive-through testing site set up by state authorities in a vacant parking lot in the southwest suburb of Aurora, Ill.

For three hours, she inched along in the torturous caravan.

“I listened to an audio book, put on music, tweeted pictures of the line,” said Hass, who works part time at a restaurant. The testing site was scheduled to close at 4 p.m., but workers stayed hours longer to help those in line. “The time it takes right now is just crazy.”

Demand at the Aurora testing site and throughout Illinois has boomed in recent weeks. In September, the site averaged 325 tests a day; now it is performing more than 1,000 daily, said Kevin Jaques. He is the spokesman for the Illinois State Covid-19 Testing Project, which runs 10 free testing sites and eight mobile sites across the state.

“The demand is exploding across the board,” Jaques said. “The labs we’re working with have asked us to cap the number we do because they can’t process them quickly enough anymore to meet the 72-hour turnaround.”

Waiting more than three days for test results renders them much less useful, health officials say, because those who have come in contact with the infected may begin to become infectious themselves. Residents are also basing their actions — such as whether to continue to isolate — on the results.

Jaques and other testing officials said they worry that the long lines and delays could dissuade people from getting tested at a time when fast and widespread testing is critical.

The resurgence of testing delays is sabotaging America’s ability to stem runaway viral transmission and the mounting lives lost. Compared with earlier in the pandemic, the country is doing far more testing — more than 1.4 million daily tests conducted in recent days, compared with 100,000 to 300,000 a day in the spring, according to the Covid Tracking Project. The project is a volunteer effort to compile data from state health agencies.

The problem is that even as the nation’s testing capacity expanded, so did demand. At first, it was driven by businesses resuming, schools reopening and people emerging from their homes. But in recent months, the record-breaking rise in infections has sent demand for tests surging even higher, outstripping the ability of labs to keep up.

In a public warning last week, the American Clinical Laboratory Association — which represents large commercial labs such as LabCorp and Quest Diagnostics — cautioned that soaring demand for coronavirus tests will soon push labs beyond their capacity, delaying results.

In addition to running out of necessary chemicals and swabs — as happened repeatedly early in the pandemic — many labs say they are running short of other equipment, such as pipettes, a laboratory tool used to carry fluid.

Testing sites say they are also experiencing shortages of workers to handle the surge.

The clinical lab group highlighted in its statement that some strategies used to increase capacity, such as pooling testing samples, are useful only “for populations at low risk or with low prevalence of infection” and could no longer be deployed with the virus now raging out of control.

In a glimmer of hopeful news, federal regulators on Tuesday approved the first rapid, at-home test — Lucira Health’s “All-In-One” test kit. The company expects to sell its test for less than $50, and it will require a prescription. While experts saw the news as an encouraging development, it will not reach the national market until early spring as Lucira scales up manufacturing, the company said.

While public health labs are not yet seeing significant delays, it is probably just a matter of time before they do, said Scott Becker, chief executive of the Association of Public Health Laboratories.

“Beyond the supply issues, the one thing people can do is all the public health measures we’ve been talking about for months now — mask up, distancing, not gathering in groups,” Becker said. “Or our testing capacity just won’t be able to keep up.”

In recent days, testing officials say, many people coming to get tested are there ahead of trips to see family or gatherings for Thanksgiving. But that may not be an entirely sound strategy, experts say.

“A test is valid only for a certain point in time. You can test negative one day and be positive the next,” Becker said. “Are these people getting tested more than once? Are they quarantining between the time they take the test and when they see people? Are they getting exposed at an airport or along their drive to see family?”

Despite experts’ warnings to take precautions ahead of the holidays, many public health experts are anticipating a jump in infections after Thanksgiving, as happened after Memorial Day, the Fourth of July, Labor Day and Halloween.

In recent days, some experts have expressed hope that the country’s testing problems will find a measure of relief under President-elect Joe Biden, who has said he plans to create a national testing board to scale up testing similar to President Franklin D. Roosevelt’s War Production Board.

“We need an interconnected system of labs. You have commercial labs that are swamped, and labs at universities with huge capacity but no great system for allocating tests to them,” said Eileen O’Connor, a senior vice president at the Rockefeller Foundation, which has been leading efforts to improve testing. “We as a country have been talking about this testing problem for months, and it’s appalling we still haven’t done what’s needed.”

The lack of a national testing strategy has become especially glaring in recent weeks as new testing technologies have emerged.

The United States now has several different types of tests to deploy against the virus: the slower-but-accurate molecular PCR tests, the rapid-but-less-accurate antigen tests (which detect proteins on the surface of the virus), new tests based on CRISPR gene-editing technology, and community surveillance that relies on testing sewage.

Experts have repeatedly recommended deploying them strategically in a multipronged approach.

In areas with low infection rates, they say, sewage surveillance tests should be used as an early warning signal. If the sewage suggests the beginnings of an outbreak, rapid tests could be deployed to test an entire community overnight. Those who screen positive on the home tests could then have their status confirmed with more precise PCR tests.

But few communities and states have done so. And President Trump’s administration has done little to advocate for such a strategy.

On Monday, Assistant Health Secretary Brett Giroir — Trump’s lead official on testing — said the administration has worked hard to expand testing, has sent millions of rapid tests to nursing homes and other facilities, and has helped states open surge testing sites.

“I don’t know where the lines are,” Giroir said. “The best way to solve the testing problems if there are any is to have public health measures. … Indoor crowded spaces, mask-wearing.”

On Wednesday — four days after enduring that hours-long line in the Chicago suburbs for testing — Sarah Hass said she was still waiting to get results. “I don’t want to get anyone at work sick, so I was trying to do the right thing,” she said.

“But I’m in my 20s. I have time to kill,” she said. “Imagine how hard this is on people who have kids, who need to hold down their job. The way testing is going right now just isn’t going to work.”