As COVID-19 cases have continued to surge across the U.S., so has the demand for testing.
Diagnostics experts are now closely monitoring several concerning and converging vectors and what could be a perfect storm of infection this holiday season. Labs and clinics administering COVID-19 tests warn that the need for testing may outstrip capacity.
"A wave of COVID-19 cases is sweeping across the United States," Quest Diagnostics, one of the largest testing companies in the U.S., said in a statement Tuesday. "Assuming national trends continue, we expect COVID-19 cases and corresponding orders for testing to increase for the foreseeable future, which may cause turnaround times to grow."
And cases are only expected to rise after Thanksgiving and Christmas, and with it a potential backlog in testing.
"We are concerned about Thanksgiving," Brett Giroir, the assistant secretary for health at the U.S. Department of Health and Human Services, told ABC News. "In terms of post-Thanksgiving surges and testing, we really are going to create as many tests as possible, of as high quality as possible. Get them to as many people as possible."
Demand for COVID-19 tests rose 50% compared to six weeks prior, Quest said, as the rate of positivity rose to more than 10%. LabCorp, another large private testing lab, likewise flagged a "rise in demand," and said their labs "are operating 24 hours a day, 7 days a week." A LabCorp spokesperson told ABC News that in the last week, it performed over 1 million tests, "the most that LabCorp has performed in a single week since the pandemic started."
American Clinical Laboratory Association President Julie Khani warned Thursday, it's a load threatening to stress the supply chain further.
"With demand for testing surging across the country, ACLA member laboratories are experiencing a significant increase in the volume of COVID-19 test orders. Clinical labs are also facing delays or cancellations on orders for critical supplies, such as pipette tips," Khani said in a statement to ABC News.
"The surge in demand for testing will mean that some members could reach or exceed their current testing capacities," Khani added.
Diagnostic labs and testing industry sources told ABC News that the sting is still raw from the virus's first surge, when scarce supplies of raw materials contributed to bottlenecked turnaround times for test results.
"I can't believe we're months into this and we are currently back to where we were this spring and early summer," Dr. David Grenache, president of the American Association for Clinical Chemistry, told ABC News. "Cases rising very quickly, limited supplies and reagents. But our biggest resource and our most precious resource are the scientists, the clinical laboratory scientists that perform the test."
Sufficient laboratory staff to process the testing influx is a concern echoed across the health care industry.
"We've been working really hard to increase our capacity. Manpower is essential for that, and it's our biggest constraint," Quest spokesperson Kim Gorode told ABC News, adding that it's preparing for an influx of both infection and demand for testing after Thanksgiving.
"We don't want to be back where we were," Gorode said.
Quest said it is "actively seeking" more staff to increase the efficiency and turnaround time of its COVID-19 testing.
"Unfortunately, we've been here before, and I think we've learned a lot of lessons," Gorode said. "We've been working really hard since summer, knowing this could come, and we've been preparing. We expect that big demand around Thanksgiving, but right now, we're still well positioned to meet it."
Giroir told ABC News that major laboratories have "assured" him that "right now, they're in good shape and are able to handle their issues," adding, the administration "will work with them like we work with everyone else on supplies, we have invested into pipette tips and all the supplies across the chain."
"Manufacturers have ramped up production as high as it could go. There is no flex in the system at this point," Kelly Wroblewski, the director of infectious diseases at the Association of Public Health Laboratories, told ABC News. "It's a big challenge, and it's a lot like whack-a-mole: One week it's plastics and pipette tips and the next week it's ethanol."
"I'm very concerned about Thanksgiving," Grenache said. "I think the Thanksgiving holiday in the United States is going to be a superspreader event like we have not seen."
The Centers for Disease Control and Prevention has provided its most robust guidelines ahead of the holidays -- as several states have issued restrictions and new cases have been tied to family gatherings -- stressing extra caution.
The steep rise in infections across the country affects labs' ability to triage test results with specimen "pooling" (testing groups of people at once) as the method is not effective in populations with high infection rates.
"We're seeing demand that we haven't seen since the beginning of the year, and you know, who knows how bad it could get," Gorode said. "The way this virus circulates -- it's not just hot spots -- it's everywhere now. And as infection increases, we may have to pull back on pool testing, and that could impact capacity."
Rapid antigen tests are now more available than they were in the summer, and some are being sold in chain stores around the country. On Tuesday evening, the Food and Drug Administration issued emergency authorization for the first at-home prescription rapid test. Though it may not be as effective as a lab test, it offers nearly instant results.
Experts emphasize testing can serve as an essential tool in stemming COVID-19's spread among contagious -- though perhaps asymptomatic -- individuals. Still, testing alone cannot prevent infection.
"COVID test results are only as good as the day in which the sample was collected," Grenache told ABC. "You could get it collected on a Monday, have a negative test result and get infected on Tuesday, and then bring it home to your family, if you travel during Thanksgiving."
"Testing doesn't make things safer," Gorode said. "We're not saying that testing is a way you can travel or celebrate Thanksgiving normally. The lab industry can only do so much and we're working so hard to meet demand, but people need to take personal responsibility as well."
LabCorp said it can test about 210,000 people a day. Quest said it can test 215,000 a day. If demand pushes past that limit, longer delays will begin to creep in.
"It's going to be tough," Gorode said. "Nobody has a crystal ball, but right now we're working hard and think we're going to be OK."
"I think Thanksgiving will be a critical juncture where we will see a lot of challenges going into the weeks after," Wroblewski said. "Help us help you. Wear your mask, stay home, social distance, because unless something changes, and if the curve continues to go up -- and I don't see any way but up right now -- at some point we will reach our limit."
ABC News' Anne Flaherty contributed to this report.