Minnesota reported its busiest stretch of COVID-19 diagnostic testing ever last week, but health leaders warned of delays in results because of national supply shortages that have temporarily reduced the state's daily testing capacity.

Mayo Clinic's national reference lab in Rochester is down to about 11,000 COVID-19 tests per day from a capacity of about 20,000, though it is prioritizing Minnesota samples, and HealthPartners' daily capacity has dropped from 2,000 to as low as 1,200.

Delayed results are frustrating for people waiting to find out if they're infected and have exposed others, or if their employers won't let them work without a rule-out test, but they are unavoidable right now, said Dr. Mark Sannes, a HealthPartners infectious disease specialist.

"As the burden of COVID-19 has really ramped up across the southern United States, the consumption of testing reagents has ramped up with it," he said. "There really is a finite supply of that nationwide. ... We are not able to get everything we're asking for."

Providers are taking steps to increase capacity and minimize wait times. The University of Minnesota recently gained accreditation for its veterinary diagnostic lab — one of the largest in the nation — to test COVID-19 samples. It can now perform 180 human COVID-19 tests per day.

Mayo switched to heavier use of its in-house COVID-19 test, which is slower but isn't as reliant on equipment that is in short supply. Waits that were 72 to 96 hours two weeks ago are now down to 24 to 48 hours in many cases.

Officials with the Minnesota Department of Health are monitoring the delays closely, because they can hinder the state's ability to track the spread of the COVID-19 outbreak and warn people of their infections before they expose others.

"That concerns us deeply," said state Health Commissioner Jan Malcolm, "because it does compromise our ability to help people isolate and quarantine quickly enough to have the full effect on mitigating the spread."

The state on Tuesday reported 52,281 infections confirmed through diagnostic testing of the virus that causes COVID-19, and 1,580 deaths. Hospitalizations on Tuesday crept up to 294 — with 138 of those patients needing intensive care.

The state only reported 9,076 diagnostic test results on Tuesday, but totals on that day of the week have been lower as they reflect reduced sample collections on weekends.

Last week was the first in the pandemic in which the state reported results for more than 100,000 diagnostic tests, which check for the virus in nasal or throat samples.

Even so, retired physician Mark Carter of Eagan said his family had trouble this week locating testing for his 17-year-old granddaughter, despite her fever and respiratory symptoms that make COVID-19 a suspicion.

CVS had no availability and her Allina Health doctor initially discouraged testing until the family pressed the health system to get her scheduled, Carter said.

"She was told all sorts of things like she wasn't sick enough to be tested. That's ridiculous," he said. "The spectrum of disease is just enormous."

Positivity rate rises

The state hasn't backed off its current broad testing guidance, which allows for the testing of people who have been exposed to COVID-19 cases but haven't developed symptoms. People with asymptomatic infections are still at risk to spread the virus to others at greater risk of COVID-19 complications.

The statewide positivity rate of COVID-19 tests has risen to nearly 5%, which Malcolm said is an early warning threshold that the spread of the virus is increasing.

Rising case rates in southern and western states over the past month eventually led to more hospitalizations and deaths. Minnesota only reported four deaths on Tuesday, though, and hasn't reported 10 or more deaths since July 2.

The state is prioritizing testing for certain populations, and for universal testing of workers and residents in long-term care facilities with outbreaks. Health officials earlier this month also discouraged testing for rule-out purposes before allowing workers to return to their jobs or children to participate in sports or camps.

"Even for individuals who have had COVID we are not recommending a test-based strategy for returning to work or any activity," said Kris Ehresmann, state infectious disease director. People are clear to return to activities 10 days after symptom onset, as long as they don't have fever or any symptoms for three straight days, she said.

Mayo has not changed its recommendations to its clinicians on who should be tested, but it is discouraging them from clogging up their lab with low-priority tests that would delay results, said Dr. Bobbi Pritt, Mayo's chair of clinical microbiology.

"Providing a result several days after the specimen was obtained just doesn't do anyone any good," she said. "When we cannot provide the turnaround time that we want, we have been limiting the tests that we are doing."

'All hands on deck'

Problems are episodic depending on which commercial testing platforms labs use, because those systems require the use of their own equipment and chemical reagents. Current shortages of supplies for the Hologic Panther system are affecting turnaround times for HealthPartners and Mayo.

Mayo is buying three new test platforms that will diversify its capacity and make its lab less sensitive to shortages from any one supplier. That addition next month will increase Mayo's capacity to as many as 30,000 COVID-19 diagnostic tests per day.

The U's addition of the vet lab to COVID-19 testing offers the same benefit, because its testing platform is different from the one used by the medical school.

The lab is handling its usual responsibilities such as surveillance of poultry or swine herds, and diagnosing outbreaks at individual farms, but it can divert more resources if needed to handle more COVID-19 tests, said Jerry Torrison, vet lab director.

"It's all hands on deck, let's solve this problem together," he said.

M Health Fairview prioritizes testing for select patients such as those undergoing surgeries, partly because of the complications that could occur during their recoveries if they were infected. The U affiliate has set up test clinics in high-need areas as well, including after the mass protests over the police killing of George Floyd in May.

North Memorial Health has two walk-up sites for asymptomatic and symptomatic people, and it is reporting a turnaround time of three to seven days for results. Further delays are possible given the national spread of COVID-19 and testing demands, though, said spokesperson Katy Sullivan.

Allina has maintained rapid turnaround of tests at its own lab, but sends most samples to external labs that are experiencing delays, said Heather Dawson, Allina's vice president for lab services.

The health system analyzes lags in test results and contacts multiple labs to decide where to send samples. Dawson said demand has shifted toward asymptomatic people with individual exposure risks and away from people whose infections could have occurred during mass protests.

"We're far enough past those," she said, "that we feel we are kind of switching out one population for another."