ST. PAUL, Minn. (AP) — Minnesota Department of Health officials said Tuesday they are investigating a COVID-19 outbreak at a camp for teenagers in the northwestern part of the state.

Communications specialist Erin McHenry said state health officials are investigating “a cluster of cases” at the Castaway Club Young Life Camp on Pelican Lake, about 45 miles east of Fargo, North Dakota. The facility typically hosts teenagers from about 10 states, camp manager Greg Johnson said.

Johnson said he’s aware of 10 virus cases involving staff members over the past two weeks, with no new infections in the last week. The number of infected guests wasn’t immediately known because cases may have been reported in other states, KVRR-TV reported.

Johnson said when the outbreak began, special protocols were put into place that included an indoor mask mandate and in some circumstances an outdoor mask requirement.

New federal guidance recommends that people in 14 mostly smaller Minnesota counties with high or substantial transmission rates wear masks, regardless of their vaccination status. Scott County is the only Twin Cities metro contest on the list. Otter Tail County, where the Pelican Lake camp is located, is not.

Meanwhile, Mayo Clinic in Rochester says it will require employees to be vaccinated against the coronavirus by mid-September, becoming one of the latest health systems to do so as delta variant cases rise around the country.

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