Minnesota on Thursday reported 2,071 coronavirus infections linked to pre-K-12 school buildings in the week ending Sept. 18, an increase from 977 the previous week and the first weekly count above 2,000 in the pandemic.

While an increase after the start of classes isn't surprising, the total more than doubles the pace last fall — when COVID-19 vaccine wasn't available for people 12 and older, according to weekly data from the Minnesota Department of Health.

The state also reported that 233 of roughly 2,500 school buildings had COVID-19 outbreaks — defined as five people who tested positive in a two-week period and were in their schools while infectious. The total last week was 96.

School COVID-19 response plans are less protective this fall, which is a concern because many are based on old notions of the coronavirus and not the fast-spreading delta variant, said Michael Osterholm, director for the University of Minnesota's Center for Infectious Disease Research and Policy.

"Part of that is our fault in public health," he said. "We told them we could do [in-person learning] safely this year."

Children are at lower risks of severe COVID-19 but can spread the coronavirus to others who are more vulnerable. Federal data show that 57 children with confirmed or suspected COVID-19 were admitted to Minnesota hospitals in the seven-day period ending Tuesday — one of the highest one-week totals since December.

School districts have scrambled to respond in the absence of an emergency order from Gov. Tim Walz — and ahead of a Friday deadline to receive federal American Rescue Plan funds. The resulting local debates have produced heated exchanges, including a physical altercation between a masked and an unmasked attendee of the Eastern Carver County Schools board meeting this week.

While public furor has focused on mask mandates, many of the plans differ significantly on testing and when to quarantine students.

The Rosemount-Apple Valley-Eagan district "strongly recommends" 10-day quarantines for unvaccinated students exposed to the virus. Minneapolis Public Schools' policy, on the other hand, indicates that unvaccinated close contacts "need to quarantine for 14 days," while the Anoka-Hennepin district sets only a 10-day requirement for unvaccinated relatives of infected students and doesn't automatically require contact tracing to find other exposed classmates.

One challenge is that more transmission appears to be occurring in schools as a result of the delta variant, said Deb Henton, executive director of the Minnesota Association of School Administrators. "Last year, the superintendents would tell you they weren't seeing the kids transmit the virus to other kids. What they were seeing was the virus was being brought in from outside. Now they are seeing it transmitted more frequently within classrooms."

Whether the increase in school outbreaks reflects the peak of the pandemic wave is unclear. Models by Mayo Clinic and the Centers for Disease Control and Prevention predict level or slight growth in infections by mid-October. Minnesota on Thursday reported a 6.7% positivity rate of COVID-19 testing, below a high last week of 7.1% but above the state's 5% caution threshold for viral spread.

The total number of inpatient beds filled with COVID-19 patients in Minnesota dropped from 801 on Tuesday to 789 on Wednesday, but remains at near-record levels for 2021. Crowding was severe enough Tuesday that Minnesota's C4 coordinating center was unable to broker any of 27 transfer requests by hospitals because they were full or their patients needed higher-level care elsewhere.

The state on Thursday also reported 2,874 more coronavirus infections and 13 COVID-19 deaths, raising totals in the pandemic to 711,094 infections and 8,153 deaths.

Testing may have undercounted the actual number of pediatric coronavirus infections through May, according to a new preprint study that examined antibody levels in blood samples from Minnesota and 13 other states. However, most children showed no signs of past infection.

"There are still many who are susceptible to the virus," said Stephanie Yendell, a co-author and senior epidemiology supervisor at the Minnesota Department of Health.

Minnesota has reported a total of 31,470 infections associated with pre-K-12 schools, which educate more than 900,000 students each year and employ more than 140,000 workers. The cases involve students or staff members who could have been exposed to the virus anywhere but were in school while infectious.

Routine testing could be contributing to the higher numbers this month and the identification of asymptomatic cases. About 30% of Minnesota's 2,500 school buildings have ordered test kits from the state.

However, many district leaders said funding and supplies are too limited to conduct routine surveillance for outbreaks or "test-to-stay" approaches in which students exposed to the virus can remain in class rather than in quarantine if they test negative each morning.

St. Paul Public Schools noted the funding shortage in an e-mail this week in which it announced a plan to offer rapid testing of any student who shows COVID-19 symptoms.

"While we know that offering COVID-19 testing at school for students could identify further cases, the limited funding available coupled with other challenges ... make it unrealistic," the district statement said.

Despite the challenges, Henton said many district leaders want control so they can adjust their responses based on local infection levels.

Albert Lea school officials remain hopeful that a quick switch to mask-wearing by all students in August helped shorten an outbreak. The district on Thursday updated its policy, indicating that the mask requirement for grades six through 12 would be revisited on Oct. 20.

Three Albert Lea schools remain on the state outbreak list, despite a decline in cases; buildings are removed only when they report no infections in a four-week period. The list includes numerous large Twin Cities high schools.

While more than 72% of Minnesotans 12 and older have received at least first doses of COVID-19 vaccine, that rate drops below 60% for the 12 to 17 age group.

Walz on Thursday urged people to seek COVID-19 vaccines or boosters when recommended. The state announced a clinic at the Minneapolis Convention Center on Sunday when new recipients will receive discounted access to the Twin Cities Con festival. Booster doses also are available at the state's Mall of America vaccine site.

Staff writers Anthony Lonetree and Mara Klecker contributed to this report.

Jeremy Olson • 612-673-7744