Minnesota, after two years and 20 million COVID-19 tests, is changing how it uses test results — away from broad surveillance of the pandemic and toward more individual medical decisions.

Positive tests no longer trigger contact tracing investigations to identify people exposed to the virus or to locate the bars and public places at the heart of outbreaks. Daily infection numbers have less importance as well because wastewater data provides a faster picture of viral growth than test results.

Still, public health officials say COVID-19 testing remains vital to Minnesota's public health response, and that people should take advantage of free state testing sites that will remain open through the summer and ahead of any potential uptick in viral spread when people head indoors for the fall and winter.

"Having someone find out that they are positive, whether it's a home test or something they do at a clinic or pharmacy or whatever, is still valuable because then they can change their choices and hopefully not spread the virus further," said Cheryl Petersen-Kroeber, director of emergency preparedness and response for the Minnesota Department of Health.

Individual results also have become more useful because they quickly qualify people under the new federal "test to treat" initiative for antiviral drugs and antibody infusions that can blunt their illnesses.

Drugs such as Paxlovid were rationed earlier in the pandemic, but are widely available if people at elevated risk of severe COVID-19 seek them early in their infections. Minnesota has used 7,000 of nearly 28,000 courses of the antiviral drug.

While some doctors require lab-provided tests, Allina Health's Dr. Frank Rhame said he considers a rapid at-home test result good enough to connect patients with treatments that can reduce the risks of COVID-19 hospitalization by 90%.

"I can't tell you the number of times people are getting a test five days or six days into their illness and it's too late for Paxlovid," Rhame said. "Anyone with respiratory symptoms, or anything that might be COVID, get yourself a test."

State health officials believe timely treatment has helped, along with strong levels of immunity from recent vaccinations and infections.

Infection numbers have surged above 1,500 per day this month, but the number of COVID-19 hospitalizations requiring intensive care has remained below 30 for 22 days. That is the second-longest stretch of low ICU usage other than last summer when COVID-19 levels were so low people prematurely hoped the pandemic was over.

Positive tests are still used in several ways, allowing health officials to alert high-risk locations such as nursing homes of outbreaks, and to remind infected individuals to follow federal health guidance and isolate from others for at least five days until they are fever- and symptom-free.

Positive samples also are submitted for genomic sequencing so public health officials can identify coronavirus variants that are spreading faster or causing more severe illness.

None of that can be done with the results of at-home rapid antigen tests, which aren't reported to public health authorities. By some estimates, half of all COVID-19 tests are now done at home.

Minnesota leaders have nonetheless supported more use of at-home tests, making 1 million available for free by mail. More than half remain available to order online.

The loss of some publicly reportable tests in exchange for more public convenience is a worthwhile tradeoff, because Minnesota never had a complete count of COVID-19 cases in the first place, said Kathy Como-Sabetti, a COVID-19 epidemiologist with the state Health Department.

Minnesota has used testing to identify nearly 1.5 million residents who have been infected, but one federal estimate suggests the actual number is more like 3.3 million people when including people who never sought testing.

Trends have always been more important than totals, and can still be tracked even with fewer reported results, she said.

"Are we going up, and are we going up quickly? Are we going down, and are we doing down quickly? Those are the things that are of value," Como-Sabetti said.

At-home tests raise other concerns, though, because they use the rapid antigen platforms that are only 40 to 60% accurate at identifying people who are infected with the coronavirus, said Dr. Bobbi Pritt, chair of clinical microbiology at Mayo Clinic. The benefit of rapid antigen testing at home or in clinics is that results come in minutes, but they have to be understood in context.

"If it's positive, you have an answer," Pritt said, "but if it's negative, it doesn't mean you don't have COVID."

The majority of COVID-19 testing in clinics and labs involves a technology called polymerase chain reaction, or PCR. It is highly accurate because it identifies evidence of viral genetic material in saliva or nasal specimens, but has its own limitations. PCR testing is so good at finding viral genetic material that it keeps doing so after someone is no longer infectious.

"Early on, we probably put too much emphasis on someone having a negative PCR result before they could go back to work or participate in activities," Pritt said.

The latest CDC guidance doesn't require a negative test to end isolation, but Pritt said a rapid antigen test is a better final check once people are symptom-free.

PCR remains a yes/no test for whether someone has COVID-19, despite research to try to use it to determine someone's level of illness. Pritt said variations in collection methods and testing equipment still make it too difficult to compare results and reliably determine which patients are sicker or more infectious than others.

PCR and rapid antigen testing are available at many state testing centers, which have performed 2.1 million tests during the pandemic. Testing levels have fallen at the state sites from 67,000 per week at the peak of the omicron pandemic wave in January to 6,800 in April, but Petersen-Kroeber said the plan is to keep them open and scale them up or down as needed.

"We just don't want to be in a position where we are scrambling to stand something back up in the fall," she said, "if we do see a shift in the virus in some way."