PORTLAND — Some Maine school districts are returning to mandatory mask usage as COVID-19 case counts in the state rise.

Bangor schools returned to a universal mask requirement on Monday. And officials in Portland, the largest school district in the state, announced Tuesday that mandatory masks are returning this week.

Portland Superintendent Xavier Botana said Tuesday in a letter to parents that rising cases make “a return to required masking the safest course at this time.” He acknowledged that the decision was “disappointing” to many.

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The seven-day rolling average of daily new cases in Maine has risen over the past two weeks from 278 cases per day on April 24 to 752 cases per day on May 8. The seven-day rolling average of daily deaths also has risen from less than one death per day on April 24 to about five deaths per day on May 8.

A handful of other mask mandates are in place around the state. Acadia National Park is requiring masks in indoor areas, and Bangor and Portland city officials have restarted requiring masks in public buildings.