Why 3% is the COVID-19 positivity rate that closes or keeps open a Milwaukee public school

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Posted at 7:03 PM, Sep 29, 2021
and last updated 2021-09-29 20:03:42-04

MILWAUKEE — Three percent of positive COVID-19 cases is the magic number Milwaukee Public Schools need to stay below in order for a school to stay open. But where that number came from is not totally clear.

The 3-percent threshold was voted on and put in place by the MPS School Board of Directors. It was used earlier this week when Lancaster School saw too many COVID-19 cases among staff and students.

“Lancaster School, which is a K-8 on the northwest side, had more than 3 percent of its staff and students contracted the COVID-19 virus. And because of that, we decided to shift to virtual learning from in-person learning,” said Bob Peterson, MPS School Board of Directors President.

In directions that came out before the start of this school year, the Wisconsin Department of Public Instruction said it has not offered any percent positive guidance for COVID-19. Instead, DPI suggests a layered mitigation strategy, which includes requiring face masks and quarantines.

Dr. Ben Weston, the chief pandemic policy adviser for Milwaukee County and associate professor at the Medical College of Wisconsin, says MPS made the decision regarding the 3 percent cutoff on its own.

“You certainly have to have some sort of cutoff. The higher disease burden makes it much more risky that you have transmission in schools. But how they got that exact number I would defer that question to them,” said Weston.

The idea of the 3-percent threshold might have first surfaced in May of 2020. The World Health Organization recommended government should be at a 5-percent positivity rate or lower for 14 days to reopen. Soon after, Harvard Global Health Institute said 3 percent was more successful. In July of 2020, the largest school district in the U.S., New York City Schools, announced it would shut down schools if the city’s percent positive rate was above 3 percent.

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Locally, the Kenosha Unified School District said 3-percent positive rate or above would trigger a school closure. The Port Washington-Saukville School District said 3 percent triggers a mask mandate.

So does a 3-percent cutoff work? Peterson says yes, arguing MPS has only had to switch two schools to virtual.

“We have over 130-some schools. Having one or two is to me an indication that a lot of our mitigation strategies are very effective," said Peterson.

MPS policy says once a school hits the 3-percent positive threshold, students need to stay virtual for 14 days before they return.

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