The Summit County Public Health Department is investigating an outbreak of 21 cases of the novel coronavirus at Alpine Dance Academy in Frisco, according to a news release.

Of the 21 cases, 16 are among employees and students at the dance academy and five are among family members of students, according to the release. The outbreak is also affecting local public schools, with multiple cohorts totaling 142 students quarantined at Summit middle and high schools.

Health officials say the outbreak was caused by students’ failure to adhere to guidelines aimed at preventing the spread of the virus, including attending class while sick.

“This is a clear example of how quickly the virus can spread in our community if basic mitigation measures are not followed,” Public Health Director Amy Wineland said in the release. “In this case, Alpine Dance Academy had implemented layered safety measures to protect their students; however, if students knowingly and repeatedly go to practice while sick, then they pose a risk to the health of their peers, family and instructors.”

County officials say the dance academy had sufficient prevention measures in place — including mask-wearing, physical distancing, symptom checking, and cleaning and disinfecting — but some students did not report their symptoms when attending class.

“We are extremely disappointed in our students for coming to dance while symptomatic and not being candid with public health officials about doing so,” Alpine Dance Academy owner Kelly Monahon said in the release. “This delayed a quarantine that could have protected a number of our dancers, staff and their family members.”

County health officials emphasized that anyone with symptoms — no matter how mild — should be tested and eliminate their contact with others until test results are received. Free testing is available daily across the county. Find information about times and locations at SummitCountyCo.gov/testing.