ST. PAUL — A team of state and federal health workers was recently confronted by armed residents while conducting random coronavirus testing in communities across Minnesota.

“The incident was unfortunate,” said Julie Bartkey, a spokeswoman for the Minnesota Department of Health. “The team did the right thing by leaving and notifying their study site coordinator of the situation.”

State officials confirmed the encounter, but have not disclosed when or where the incident occurred.

Health officials are conducting random testing of households in 180 communities across Minnesota as part of a survey to better understand the spread of COVID-19. The study is being done with the help of the federal Centers for Disease Control and Prevention.

State health leaders have encouraged households to participate in the study if asked. It includes an interview and testing for active COVID-19 infections as well as virus-fighting antibodies that would signal a previous exposure.

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“The vast majority of neighborhoods have been friendly, but we will continue to monitor for concerns as we move through different areas of the state,” Bartkey said. “It could have been a simple misunderstanding, we simply don’t know.”

Health officials have not disclosed where the surveys are being conducted. They’ve said the areas were chosen by population density from U.S. census data.

Only households chosen at random can participate.

The confrontation came to light after at least two Twin Cities metro police departments posted to their social media accounts the text of an email from the Minnesota Department of Public Safety. The messages describes the study and notes the health workers conducting it have credentials that identify them.

“The households are randomly selected so examiners will be out knocking on doors,” the message says. “I am sending this email because a team of MDH and CDC examiners was recently confronted by a group of armed citizens while out in a neighborhood.”

A spokesman for the Department of Public Safety did not immediately return a message seeking comment.

Community transmission, when someone gets sick without knowingly being in contact with an infected person, is the largest source of transmission in the state. The random testing study is part of an effort to better understand how the coronavirus is being transmitted.