Eagle County reported more COVID-19 cases Monday than on any other day during the pandemic, and the average number of daily cases confirmed there has tripled in a week, local data show. 

It is “highly likely” that the surge is being caused by the omicron variant, the state health department said Monday.

The county averaged about 15 cases per day on Dec. 12, a recent low as it and the rest of the state slowly emerged from the fall surge. But that average has nearly tripled in the days since – to more than 43 cases per day by Sunday. The county reported 105 new cases Monday, the most it has identified in a single day during the pandemic, according to the Eagle County Public Health website. 

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A spokesperson for the state Department of Public Health and Environment said Monday that “sequencing is pending” to confirm omicron is driving the spread in the county. But the Eagle County samples contain a telltale marker that indicates the presence of the new variant, the spokesperson and Gov. Jared Polis said this week.

“That, plus their rapid rise, suggests it is highly likely that omicron is circulating there,” the spokesperson said in an email Monday night. 

Messages sent to public health officials in the county were not returned Tuesday. On Friday, Eagle County Public Health issued a public health advisory warning of the “sharp increase in cases.” 

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“This is an indication that community spread is very high and the likelihood for exposure has increased considerably,” the agency wrote. “In addition, local testing is quickly reaching its capacity and persons with symptoms will be prioritized for testing.”

Speaking at a news conference Tuesday, Polis said omicron was spreading in areas with recent travel, highlighting Eagle, Summit and Pitkin counties specifically. Pitkin confirmed its first omicron case Tuesday. The governor said officials expected the parts of Colorado with “significant visitation” to be hit by omicron first.

All three of those counties have vaccination rates of over 80%, and Polis said officials weren’t as worried about residents there because of those rates. But he said the state wants to make sure Colorado is a safe place for non-Coloradans to visit.

“At this point, we can essentially confirm that transmission of omicron variant in Colorado is occurring,” he said. “It still is not the predominant strain in Colorado, but based on what has occurred elsewhere, we expect omicron to increase even as we continue to see delta to decrease, which is what we’ve been seeing the last few weeks.”

He added that it is a matter of “days or weeks” until omicron becomes the dominant strain here. 

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Omicron was only officially identified a month ago but has surged to become the dominant variant in the United States. The Centers for Disease Control and Prevention said Monday that the latest strain accounted for 73% of cases in the country over the past week. 

In Colorado, the variant has been identified in several counties, including Denver, Arapahoe, Jefferson, Boulder, Pitkin, El Paso and Garfield. The cases in Denver and Garfield counties have been linked to community transmission, as opposed to infections picked up while traveling. Wastewater sampling has also indicated traces of the variant in various systems around the metro area.

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Though it’s now believed omicron is more transmissible than the initial form of the virus, it remains unclear if it’s more severe than that strain or the delta variant, which remains dominant in Colorado. The impact of omicron on Colorado will in part hinge on that question, experts said.

“Omicron is here for sure with last week’s surge in Eagle County probably a signal,” said Jon Samet, dean of the Colorado School of Public Health. “The good news is that omicron will arrive while delta is descending, easing the strain on the medical care system. From what we know in other countries, omicron will likely rise steeply because of its transmissibility and immune escape. The impact on health care and on Coloradans will depend on its virulence.”