The vials of saliva arrive at the loading dock by the box-load, often just before midnight.

Dispatched from COVID-19 testing sites across the state, the cardboard boxes show up in UPS trucks at a lab in Oakdale, bearing the results of thousands of Minnesotans who spat into tiny plastic tubes earlier that day.

As many as 20,000 saliva test specimens arrive each day at the nondescript lab that processes Minnesotans' free COVID tests coming from public testing sites or through the Department of Health's mail-order test program.

The samples are treated with a bluish chemical to deactivate and preserve any virus before shipment. The tubes are disinfected at testing sites before shipment. They're disinfected again at the lab.

"They don't sit still for long," said Jennie Ward, a Cass Lake native who is lab manager at the Oakdale facility run by New Jersey lab firm Infinity BiologiX (IBX). "We get a lot of shipments between 10 p.m. and midnight. Our 6 a.m. crew comes in so that by noon those samples are done."

Saliva testing is poised to expand in 2021 in Minnesota.

Starting this month, the Minnesota Department of Health is eliminating nasal-swab testing at its 20 "barrier-free" COVID-19 testing sites, and moving to collecting only saliva samples. The state's at-home tests will remain saliva-based.

The IBX lab in Oakdale opened last fall with a capacity for up to 30,000 tests per day, and an ability to expand in 10,000-test increments if ever needed, said Dr. Andrew Brooks, IBX chief executive.

"We stood up this lab and were operational in about eight weeks, which is unheard of," he said. "It's absolutely expandable. It really depends on how Minnesota continues to approach their testing."

State Department of Health officials say the lab averaged 60,000 tests a week in December. The move to all-saliva testing is expected to add about 2,500 per week.

The arrangement with IBX relies on another private New Jersey company called Vault Health, which runs the state's community testing sites and uses telehealth and medical-data management platforms to communicate testing results. The e-mails letting people know whether their tests are positive come from Vault.

Minnesota was among a small vanguard of states in 2020 that offered free, widespread testing, using about $150 million in state funds to supplement federal funding. Private insurers are billed for the tests before the state kicks in.

Mayo Clinic Laboratories in Rochester, whose participation in the public testing program along with the University of Minnesota was hailed as a breakthrough last spring, will no longer process test specimens from the public testing sites.

Officials with Mayo and the Department of Health confirmed to the Star Tribune that while the nasal-swab testing won't be used at the community testing sites, the contract last spring that established the nasal testing capacity remains active. Nasal-swab testing remains available at private providers.

Minnesota, which has 5.7 million residents, processed about 5.6 million tests in 2020 between its public testing programs and the hundreds of private clinics, hospitals and other private sites around the state.

All told, about 415,000 of those tests positively detected genetic traces of the virus that causes COVID-19.

Latest statistics

On Sunday the Minnesota Department of Health added 2,712 cases of COVID-19 to the state's tally, and 53 additional deaths. The youngest person who died was in their 40s.

It's hard to discern trends from those figures because they include two days of data, and also the state's community testing sites were closed Thursday and Friday.

Minnesota's large COVID testing capacity did not emerge by accident.

The CEOs of IBX and Vault Health said in interviews last week that Gov. Tim Walz and his administration pursued one of the most aggressive public-testing programs in the nation.

"I think Gov. Walz's team is probably the most innovative of any state we work across — and we work across all of them," Vault Health CEO Jason Feldman said. "There is no other state that has said to their residents, anybody who needs a test can get a test, without any friction."

The lab in Oakdale is housed on a single floor of one building within a sprawling corporate campus that once served as the headquarters for the data-storage company Imation.

IBX is a recently formed, private equity-backed company that was spun out from Rutgers University last August. The Oakdale lab opened in October.

Before the spinout, IBX's predecessor — RUCDR Infinite Biologics — secured the nation's first FDA authorization for a saliva test for COVID-19. That test is now free to any Minnesota resident, by mail or at a walk-up site.

At the Oakdale lab, specimen vials are cleaned, opened and moved through a series of rooms each containing different lab equipment.

A 300-microliter sample from each vial is measured out by a machine and squirted into an individual well in a tray of specimens. Then the specimens go through another machine to isolate genetic material called RNA, and another to amplify any viral RNA for detection. IBX workers operate all of the machines.

The last stop in the testing process is a room containing the much-discussed PCR machines, known in the industry as "thermal cyclers."

IBX runs Thermo Fisher QuantStudio 5 thermal cyclers. They look like standard desktop office technology, with a touch screen and USB port in front. But rather than making copies, these machines detect bits of COVID RNA.

Once obtained, results are sent though the cloud to Vault, which distributes them.

The Infinity BiologiX TaqPath SARS-CoV-2 Assay looks for reactions with three different genes in the coronavirus. That should make it more accurate over time than tests that target a single gene, IBX CEO Brooks said.

But has making the test freely available in Minnesota lowered transmission rates, as intended? No published study quantifies that today. Rates of newly diagnosed cases have risen sharply, and fallen sharply, since October.

A study in the January issue of Health Affairs examines testing and transmission levels in 173 countries from March to June 2020, finding more testing per capita was the most influential factor associated with lower viral spread.

The study found no single optimal testing level. Increases at any level were associated with lower transmission rates in the observational data set.

"We provide empirical evidence that testing intensity was the common factor explaining the success of places that achieved near-elimination, such as China, Cambodia, and New Zealand, and the most important predictor of performance elsewhere," the authors concluded.

Joe Carlson • 612-673-4779