Editor’s note: This story has been updated to correct that one of the hosts tested positive. The other positive test was an attendee.

A Labor Day weekend party at a short-term rental in Breckenridge lead to an outbreak of at least two cases of the novel coronavirus, according to a news release.

The Summit County Public Health Department is investigating the outbreak, in which two people tested positive for the virus. An estimated 21 people attended the party at the rental unit, which was rented from Sept. 4-5.

Gathering sizes are limited to 10 under the county’s current safer-at-home public health order.

The two hosts of the party, one of whom tested positive, and the attendees are all believed to be out-of-county visitors who have returned to the Denver metro area, according to the news release.

However, the two hosts of the party have not been willing to release information about the attendees to the public health department, so officials have been unable to confirm whether any Summit County residents attended the party, according to the release. The county is currently reviewing whether the size of the gathering or the decision to withhold information constitutes a public health violation, which could lead to a fine of up to $5,000.

“This is an example of how easily the virus can spread during social gatherings and how it can be impossible to know if friends or family members might be carrying the virus,” Summit Public Health Director Amy Wineland said in the release.

The rental unit is managed by Breck Mountain Management, which disclosed that the reservation was made for six people. The management company has been cooperative with the department and is working to sanitize the rental unit, according to the release.

Wineland encouraged people to continue following the county’s six commitments of containment, which include wearing a mask, washing hands, staying 6 feet apart, staying home if when sick, getting tested if sick and getting a flu shot.

People who believe they might have been exposed to the virus at the party should call 970-668-5584 to receive a test screening from Centura Health.