At-home testing limits Minnesota COVID-19 surveillance

The popularity of over-the-counter COVID-19 tests has blurred Minnesota's pandemic surveillance, but state officials urge people to use them to identify infections and protect others from the looming omicron wave.

State Health Commissioner Jan Malcolm said she has seen estimates that two-thirds of COVID-19 tests nationwide involve rapid antigen at-home tests purchased in pharmacies, groceries and even gas stations.

That doesn't mean that two-thirds of infections are found by at-home tests, which people often use as a precaution before visiting family and friends, she noted. But they are reducing Minnesota's count of COVID-19 cases, because the state doesn't collect at-home test results.

"We're tracking what we can, but we're mindful that it's a less and less complete picture all the time," Malcolm said. "And that's true nationally. There's a lot of conversations happening about, 'How should we be trying to measure things now?' "

The measurement concerns are emerging along with the prospect of another COVID-19 wave fueled by the fast-spreading omicron variant. Minnesota on Wednesday reported another 4,149 infections and 71 COVID-19 deaths, raising its pandemic totals to 1,049,310 infections and 10,671 deaths.

COVID-19 hospitalizations crept back to 1,405 on Tuesday after declining to 1,311 on Jan 1. The positivity rate of COVID-19 testing in Minnesota surged to 13.4% in the seven days ending Dec. 28, but that rate was inflated by the low number of people who sought testing during the holidays.

Some Minnesotans are frustrated over the lack of reporting of at-home tests. Some want to help by disclosing their results. Others have relied on the state's COVID-19 case count before deciding to travel, go into office or wear masks — even though it was always an undercount because of the number of asymptomatic people who never sought testing.

People with unreported infections might be more likely to go about usual routines and spread the virus, she said.

"How many of these individuals are subsequently going to work and infecting others as a result of many employers stopping COVID pay?"

The Minnesota Department of Health doesn't collect at-home test results because it can't verify them, the agency said in a statement. "We can't be certain of what's being 'called in' and our case definition for COVID cases includes laboratory confirmation."

The state anticipates an unprecedented surge in COVID-19 testing after the holidays and is adding three free testing sites this month. Chain pharmacies have tried to maintain limited supplies of at-home tests for more people as well; Walgreens last month allowed customers to buy only four tests at once while CVS set its limit at six.

Malcolm said other metrics of COVID-19 activity are going to become more important for tracking changes in the pandemic. COVID-19 hospitalizations are a more stable metric, for example, because any rise or fall in testing isn't going to affect when the sickest people need care.

A decline in reported test results won't affect Minnesota's use of genomic sequencing to identify the variants that are circulating. Only 20% of positive specimens at most are selected for sampling by the state's network of public and private labs each week.

The state as of last week had verified only 84 infections involving omicron through genomic sequencing. However, standard COVID-19 testing fails to identify one of three gene targets when an infection involves omicron, and that serves as a preliminary indicator even without sequencing.

The so-called S gene target failure was identified in 11,176 positive tests out of 12,428 collected by IBX, a private lab on contract with Minnesota, from Dec. 27 to Jan. 1. So, presumably, almost 90% of those samples involved omicron.

Some researchers believe the testing of wastewater should become a more reliable and prominent indicator of pandemic spread. Scientists have closely tracked changes in COVID-19 prevalence in the Twin Cities by extracting viral material from sewage running through the Metropolitan Wastewater Treatment Plant in St. Paul and sending it for analysis to the University of Minnesota Genomics Center.

This approach found omicron in wastewater in mid-December and works as a public health measure because it anonymously collects samples from the entire community, said Kenny Beckman, director of the U genomic center.

Over time, wastewater data has risen and fallen with COVID-19 case numbers and the latest trend doesn't bode well for the immediate future, said Steve Balogh, a research scientist at the Met Council.

"The last five days of 2021 were the highest levels we've seen at any time in terms of the load of virus coming into the metro plant."

Regardless of case counts, Malcolm said the growing spread of omicron is obvious and people should take precautions such as mask-wearing and social distancing.

"Act as if in any crowd you are in, there's going to be omicron," she said. "Take precautions. Be mindful of where you are choosing to go and how to go and please, please, please be boosted if you can and vaccinated."

Mayo Clinic modeling predicts that Minnesota's COVID-19 case rate will double in 14 days. Early signs indicate that omicron infections produce fewer severe illnesses, so people should be mindful of whether to seek care from an overworked medical system, said Dr. Gregory Poland, leader of Mayo Clinic's COVID-19 vaccine research group.

People still should notify clinicians of positive infections so they can respond quickly if symptoms worsen, he added.