UW Medicine on Thursday said it was struggling to keep up with coronavirus testing demand and would begin to limit appointments to only those with COVID-19 symptoms or known exposures — a change prompting new questions as the omicron variant surges through the state.

The continued strain on the region’s testing capacity could mark a shift in the battle against the pandemic, as more Washingtonians rely on at-home rapid tests, rather than those in labs where samples can be genetically sequenced to monitor for new variants.

The state might soon have to start thinking of new surveillance strategies, the state’s chief science officer, Dr. Tao Kwan-Gett, said in a state Department of Health briefing Thursday.

Further complicating matters, some confusion is emerging nationwide over how to best limit viral spread as federal health experts release more information about the efficacy of rapid tests and new isolation and quarantine guidelines.

UW Medicine cited an “astronomically high” positivity rate that’s slowing its testing process and prompting the move to limit eligibility at its sites. Meanwhile, three of the health care system’s 12 testing clinics will close all together: in Ballard, at Seattle City Hall and at Lake Sammamish State Park. The changes go into effect Tuesday.

After that, people without symptoms who want to get tested before travel or gatherings, for example, will no longer be able to make appointments at UW testing sites.

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The high positivity rate — measuring more than 40% at some South King County locations — is creating a challenge in the testing system and slowing scientists’ ability to parse out which samples are actually positive, Dr. Geoff Baird, chair of laboratory medicine and pathology at UW Medicine, said in a news briefing Thursday morning.

“This isn’t an announcement that I’d like to make and we’re going to try and get back to our normal testing capacity as soon as we can,” Baird said.

While he acknowledged the temporary change will likely be inconvenient for many people, he added there “really aren’t too many ways around this.”

“We are in the midst of the worst public health disaster in the history of humanity in terms of raw numbers of people who have been impacted and people who have died,” he said. “So it’s important to go back and remind ourselves that this isn’t really an inconvenience. This is a serious public health problem right now.”

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Limits of “pool testing”

UW scientists normally opt for a “pool testing” system — common throughout the country — to speed up the process, which means they take four or five samples from testing sites, extract a small portion of each, then mix them together in one vial for testing.

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“If that sample was negative, all of those samples would be considered negative because the test is extremely sensitive,” Baird said. “So we would really have done the work of four or five tests with just one test. It was a way to increase capacity.”

He continued, “The problem when the positive test rate gets very high, though, is that all of the pools are positive. If one or two of them are … positive, we’d still have to go back and test all four individually to see which [individual sample] was positive — so we can’t do pooling anymore.”

That significantly decreases capacity, he said.

At King County’s UW collection site in Auburn, the COVID positivity rate was 49% earlier this week, Baird said. In the past, scientists have seen 5% to 10% positivity rates at Seattle sites in between surges, and at previous peaks positive rates have been around 20% to 25%, he added.

The change will last until scientists have confirmed samples’ positivity rate has fallen back down to an average of below 10% to 15%, Baird said.

Overall, most recent data shows the positivity percentage is about 25% — while test sites in South King County are between 40% and 50%, others in the Seattle area are much lower — so the rate will need to go down by about half for labs to “operate at full strength,” Baird said.

“It was expected, but it’s still been the highest we’ve ever seen in our region,” he said.

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On Thursday, the state reported another record-breaking daily number of COVID infections at 6,888, topping the most recent high recorded on Christmas Eve last week. Hospitalizations remain far lower than during previous peaks, though they’ve recently started to creep back up in some parts of Western Washington, state health leaders said last week.

Anyone who has an appointment before Tuesday will still be able to hold onto their time slot regardless of symptoms or exposure.

“[The restrictions] could change in a matter of days,” Baird said.

Avalanche of tests

Baird said the UW Medicine lab has generally been receiving 10,000 to 15,000 samples per day for most of December, with a pre-Christmas peak at 20,000 tests per day. If scientists want to get results out within 24 hours or less, they’ll have to scale back capacity to about 8,000 to 10,000 tests per day, Baird said.

“We could accept more tests, but we wouldn’t get to them in a meaningful time,” he said. “ … In the last few days, we’ve gotten to the point where our turnaround times have sometimes exceeded two days, and medically speaking, a COVID test that’s not back for several days just isn’t terribly meaningful because someone could go on and spread the virus and they wouldn’t have the important information they need to make the decision about whether or not to quarantine or limit contact, isolate, etc.

“We are making this decision because we want to keep the medical value of the testing intact,” he added.

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Baird pointed to staffing shortages as another large reason why the positivity rate is posing such a problem.

“Just like many of our other industries in medical and biomedical fields are having hiring crises right now, so are we,” he said.

UW locations have performed more than 4 million COVID tests since the beginning of the pandemic.

Baird reminded the public Thursday that “testing is one tool in the tool belt” for fighting viral spread, but that vaccines, distancing and limiting social gatherings are perhaps more important.

“COVID is not transmitted because of a lack of testing,” he said. “COVID is transmitted by human behavior with people interacting and being in close contact.”

Still, he acknowledged that the health care system will not be able to keep track of the total number of infections as accurately as long as appointments are limited.

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But, he said, the city and state have long known infection numbers are being undercounted because not everyone who gets sick gets a test. In addition, those who test positive with an at-home rapid test don’t always report their results to public health agencies.

While the positivity rate is still a “very good surrogate for what’s out there,” Baird said, a lack of total available samples — and therefore more limited sequencing — could become a problem.

Other testing options

While the UW Medicine changes leave many Washingtonians at odds over how to control asymptomatic spread in the near future, Lacy Fehrenbach, the state’s deputy secretary for COVID response, reminded the public Thursday there are still other ways to get tested — including through mobile test sites, public health department clinics and at-home testing.

For example, King County, in hopes of supporting high testing demand, plans to distribute 300,000 coronavirus at-home test kits to community groups, health centers, libraries and other congregate locations beginning in early January, County Executive Dow Constantine announced this week.

The move aims to bolster community supply of at-home rapid tests, which Walgreens, CVS and Bartell Drugs continuously report are being snatched up at a rate that’s outpacing supply.

While new research from the Food and Drug Administration shows rapid tests “may have reduced sensitivity” at detecting the omicron variant, a National Institutes of Health director added this week that even with reduced performance, rapid tests “will still pick up infections and … help individuals get treatment sooner.”

While additional information about testing and omicron spread emerges, Baird said Thursday that lab scientists will continue to monitor positivity rates every day and hopefully reopen to full capacity soon.

“We have been doing an awful lot to help out,” he added. “This is just to get us through this next surge.”

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